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LTC1695 SMBus/I2C Fan Speed Controller in SOT-23
FEATURES
s s
DESCRIPTIO
s
s s s s
Complete SMBus/I2CTM Brushless DC Fan Speed Control System in a 5-Pin SOT-23 package 0.75 PMOS Linear Regulator with 180mA Output Current Rating 0V to 4.922V Output Voltage Range Controlled by a 6-Bit DAC Simple 2-Wire SMBus/I2C Interface 250ms Internal Timer Ensures Fan Start-Up Current Limit and Thermal Shutdown Fault Status Indication via SMBus Host Readback
The LTC(R)1695 fan speed controller provides all the functions necessary for a power management microprocessor to regulate the speed of a 5V brushless DC fan via a 2-wire SMBus/I2C interface. Fan speed is controlled according to the system's required temperature profile and permits lower fan power consumption, longer battery run time and lower acoustical generated noise versus systems that only provide simple on-off control for the fan. The LTC1695 incorporates a 180mA low dropout linear regulator, a 2-wire SMBus/I2C interface and a 6-bit DAC. Fan speed is controlled by varying the fan's terminal voltage through the output voltage of the LTC1695's linear regulator. The LTC1695's output voltage is programmed by sending a 6-bit digital code to the LTC1695 DAC via the SMBus. To eliminate fan start-up problems at lower fan voltages, users can enable the LTC1695's boost start feature that provides the DAC's full-scale output voltage for 250ms before decreasing to the programmed output voltage. The LTC1695 includes output current limiting and thermal shutdown as well as status monitors that can be read back by the microprocessor during fault conditions. The LTC1695 is available in a 5-lead SOT-23 package.
APPLICATIO S
s s s s s s s
Notebook Computers Spot Cooling Portable Instruments Battery-Powered Systems DC Motor Control White LED Power Supplies Programmable Low Dropout Regulator
, LTC and LT are registered trademarks of Linear Technology Corporation. I2C is a trademark of Philips Electronics N.V.
TYPICAL APPLICATION
5V 1 VCC VOUT 5
LOAD CURRENT (mA)
Fan Voltage and Current vs DAC Code
120 100 80 ILOAD 60 40 20
1695 * TA01
VCC = 5V TA = 25C
+
10F 2
LTC1695 GND 4 4.7F
+
5V DC FAN SUNON KDE0502PFB2-8 0.6W, 1.7 CFM (25 * 25 * 10)mm3
3 SYSTEM CONTROLLER
SCL
SDA
0
0
10
U
6 5
OUTPUT VOLTAGE (V)
U
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4 VOUT 3 2 1 0 70
20
40 30 DAC CODE
50
60
1695 * TA02
1
LTC1695
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW VCC 1 GND 2 SCL 3 4 SDA 5 VOUT
Terminal Voltages Supply Voltage (VCC) ............................................. 7V All Other Inputs ........................ -0.3V to (VCC + 0.3V) Operating Temperature Range ..................... 0C to 70C Junction Temperature ........................................... 125C Storage Temperature Range .................. -65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1695CS5 S5 PART MARKING LTIY
S5 PACKAGE 5-LEAD PLASTIC SOT-23
TJMAX = 125C, JA = 256C/W SEE THE APPLICATIONS INFORMATION SECTION.
Consult factory for Industrial and Military grade parts.
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V unless otherwise stated.
SYMBOL VCC ICC DAC DAC Resolution VLSB VOS DNL INL VFS VZS RON(P) VUVLO TBST_ST TTHERMAL IFAULT VIH VIL IIN CIN tON tOFF VOL 1LSB Resolution Offset Error Differential Nonlinearity Integral Nonlinearity VOUT, DAC Full Scale VOUT, DAC Zero Scale P-Channel On Resistance Undervoltage Lockout Voltage Boost Start Timer Thermal Shutdown Temperature Output Current Limit Threshold Input High Threshold Input Low Threshold Input Current Input Capacitance Switch On Time from Stop Condition (fSMBus = 100kHz) Switch Off Time from Stop Condition (fSMBus = 100kHz) SDA Output Low Voltage SCL, SDA = 0V or 5V (Note 3) VOUT from Zero Scale to Full Scale, ILOAD = 1mA, CLOAD = 4.7F VOUT from Full Scale to Zero Scale, ILOAD = 150mA, CLOAD = 4.7F IPULLUP = 3mA
q q q
ELECTRICAL CHARACTERISTICS
PARAMETER Supply Voltage Range Supply Current, Operating Supply Current, Shutdown
CONDITIONS VOUT = Full Scale, ILOAD = 150mA DAC Code = 0 Guaranteed Monotonic ILOAD = 1mA ILOAD = 1mA ILOAD = 1mA (Note 2) ILOAD = 1mA (Note 2) ILOAD = 20mA ILOAD = 150mA RLOAD = 1k ILOAD = 150mA Rising VCC ILOAD = 10mA, CLOAD = 4.7F (Note 3) VOUT = 0V, DAC Code = 63
q q q q q
MIN 4.5
TYP 5 150.7 80 6
MAX 5.5 155 200
UNITS V mA A Bits
q q q q q q q q
73
78
83 1 0.75 0.75
4.5 4.5
4.93 4.9 0 0.75 85
Timer and Thermal Shutdown 2.3 75 180 2.1 0.8 0.1 3 50 150 150 500 500 400 5 2.9 250 155 390 850 3.5 1000 V ms C mA V V A pF s s mV
SMBus SCL, SDA Inputs
q q q
2
U
mV LSB LSB LSB V V mV
W
U
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WW
W
LTC1695
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V unless otherwise stated.
SYMBOL fSMB tBUF tHD(STA) tSU(STA) tSU(STO) tHD(DAT) tSU(DAT) tLOW tHIGH tf tr PARAMETER SMBus Operating Frequency Bus Free Time Between Stop and Start Hold Time After (Repeated) Start Condition Repeated Start Condition Setup Time Stop Condition Setup Time Data Hold Time Data Setup Time Clock Low Period Clock High Period Clock/Data Fall Time Clock/Data Rise Time CONDITIONS
q q q q q q q q q q q
ELECTRICAL CHARACTERISTICS
SMBus TIMING (Note 4)
MIN 10 4.7 4.0 4.7 4.0 300 250 4.7 4.0
TYP
MAX 100
UNITS kHz s s s s ns ns s
50 300 1000
s ns ns
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: INL, DNL specs are specified under a 1mA ILOAD condition to keep the linear regulator from operating in dropout at higher DAC codes. DNL is measured from code 0 to code 63, taking into account the untrimmed offset at code 0. Please refer to the Definitions section for more details.
Note 3: This typical specification is based on lab measurements and is not production tested. Note 4: Guaranteed by design and not tested. Please refer to the Timing Diagram section for additional information.
TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage vs DAC Code
6 5
OUTPUT VOLTAGE (V) 250
VCC = 5V TA = 25C ILOAD = 1mA SUPPLY CURRENT (A)
4 3 2 1 0
SUPPLY CURRENT (A)
0
10
20
30 40 DAC CODE
UW
50
1695 * G01
No Load Supply Current vs Supply Voltage
250
No Load Supply Current vs Temperature
VCC = 5V
TA = 25C CODE 63 200
200
CODE 63
150
150
100
CODE 0
100
CODE 0
50
50
60 63
0
4.0
5.0 4.5 5.5 SUPPLY VOLTAGE (V)
6.0
1695 * G02
0 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
1695 * G03
3
LTC1695 TYPICAL PERFOR A CE CHARACTERISTICS
Ground Current (Dropout Mode) vs Supply Voltage
900 TA =25C ILOAD = 180mA CODE 63 700
GROUND CURRENT (A)
DROPOUT VOLTAGE (mV)
GROUND CURRENT (A)
800
600
500
400
4.0
5.0 4.5 5.5 SUPPLY VOLTAGE (V)
Output Voltage (Full Scale) vs Load Current
4.930 4.920
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
4.910 CODE 63 4.900 4.890 4.880 4.870 4.860
OUTPUT VOLTAGE (V)
0
20
40
60 80 100 120 140 160 180 LOAD CURRENT (mA)
1695 * G07
Output Voltage (Midscale) vs Temperature
2.510 2.505
OUTPUT VOLTAGE (V)
VCC = 5V CODE 32 ILOAD = 1mA
2.500 2.495 2.490
DNL (LSB)
INL (LSB)
ILOAD = 150mA 2.485 2.480 -50 -25
50 25 75 0 TEMPERATURE (C)
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UW
1695 * G04
Ground Current (Dropout Mode) vs Temperature
900 850 800 CODE 63 750 700 650 600 -50 -25 VCC = 5V ILOAD = 180mA
175 150
Dropout Voltage vs Load Current
VCC = 5V TA = 85C 125 100 TA = 25C 75 50 25 0 TA = - 40C
6.0
50 25 75 0 TEMPERATURE (C)
100
125
0
20
40
60 80 100 120 140 160 180 LOAD CURRENT (mA)
1695 * G06
1695 * G05
Output Voltage (Midscale) vs Load Current
2.505
4.95
Output Voltage (Full Scale) vs Temperature
VCC = 5V CODE 63 4.93 ILOAD = 1mA
VCC = 5V TA = 25C
VCC = 5V TA = 25C
2.500
2.495 CODE 32 2.490
4.91 ILOAD = 150mA 4.89
2.485
4.87
2.480 0 20 40
60 80 100 120 140 160 180 LOAD CURRENT (mA)
1695 * G08
4.85 -50
-25
50 0 75 25 TEMPERATURE (C)
100
125
1695 * G09
Differential Nonlinearity (DNL)
0.25 VCC = 5V ILOAD = 1mA 0.25
Integral Nonlinearity (INL)
VCC = 5V ILOAD = 1mA
0.15
0.15
0.05
0.05
-0.05
-0.05
-0.15
-0.15
100
125
-0.25
0
10
20
30 40 CODE
50
60 63
1695 * G11
-0.25
0
10
20
30 40 CODE
50
60 63
1695 * G12
1695 * G10
LTC1695 TYPICAL PERFOR A CE CHARACTERISTICS
POR and UVLO vs Temperature
3.00
350 TA = 25C ILOAD = 10mA
BOOST START TIMER (ms)
SUPPLY VOLTAGE (V)
2.90
300
BOOST START TIMER (ms)
POR (RISING VCC)
2.80
UVLO (FALLING VCC)
2.70
2.60 -50
-25
0 25 50 75 TEMPERATURE (C)
Current Limit Threshold vs Supply Voltage
425 TA = 25C 400 CURRENT LIMIT (mA)
CURRENT LIMIT (mA)
JUNCTION TEMPERATURE INCREASE (C)
375
350
325
300
4.5
5.0 4.75 5.25 SUPPLY VOLTAGE (V)
Load Transient Response Code 32, 5mA to 55mA
VOUT (AC) 20mV/DIV
ILOAD 50mA/DIV 100s/DIV VCC = 5V COUT = 4.7F TANTALUM
UW
100
1695 * G13 1695 * G16
Boost Start Timer vs Supply Voltage
600 500 400 300 200 100 150 4.0
Boost Start Timer vs Temperature
VCC = 5V ILOAD = 10mA
250
200
125
5.0 5.5 4.5 SUPPLY VOLTAGE (V)
6.0
1695 * G14
0 -25
0
25 50 TEMPERATURE (C)
75
100
1695 * G15
Current Limit Threshold vs Temperature
600 VCC = 5V 500 400 300 200 100 0 -40
120 100 80 60 40 20 0
Junction Temperature Increase vs Load Current
VCC = 5V, TA = 25C, SOT-23 THERMAL RESISTANCE = 150C/W (PCB SOLDERED) SEE APPLICATIONS INFORMATION. CODE 16 (1.25V)
CODE 32 (2.5V)
CODE 48 (3.75V) CODE 63 (4.922V) 0 20 40 60 80 100 120 140 160 180 LOAD CURRENT (mA)
1695 * G18
5.5
-20
0 20 40 TEMPERATURE (C)
60
80 90
1695 * G17
Load Transient Response Code 32, 50mA to 100mA
VOUT (AC) 10mV/DIV
ILOAD 50mA/DIV 100s/DIV VCC = 5V COUT = 4.7F TANTALUM
1695 * G19
1695 * G20
5
LTC1695 TYPICAL PERFOR A CE CHARACTERISTICS
Load Transient Response Dropout (Code 63), 5mA to 55mA Load Transient Response Dropout (Code 63), 50mA to 100mA Boost Start Timer
VOUT (AC) 20mV/DIV
ILOAD 50mA/DIV 100s/DIV VCC = 5V COUT = 4.7F TANTALUM
PIN FUNCTIONS
VCC (Pin 1): Power Supply Input. VCC supplies current to the internal control circuitry, serves as the reference for the 6-bit DAC and acts as the power path for the P-channel low dropout linear regulator. Bypass VCC directly to ground with a low ESR capacitor 10F. GND (Pin 2): Ground. Tie GND to the ground plane. SCL (Pin 3): SMBus Clock Input. Data is shifted into SDA on the rising edge of the SCL clock signal during data transfer. SDA (Pin 4): SMBus Bidirectional Data Input/Digital Output. SDA is an open drain output and requires a pull-up resistor or current source to VCC. Data is shifted into SDA and acknowledged by SDA. VOUT (Pin 5): Linear Regulator Output. Connect directly to the fan's +VE terminal. VOUT is set to VZS (code 0) on power-up. For good transient response and stability, use a general purpose, low cost, medium ESR (0.1 to 1) tantalum or electrolytic capacitor. LTC recommends a surface mount tantalum capacitor of 4.7F.
6
UW
VOUT (AC) 20mV/DIV
VOUT 2V/DIV
ILOAD 50mA/DIV 100s/DIV VCC = 5V COUT = 4.7F TANTALUM
VCC = 5V CIN = 10F COUT = 4.7F ILOAD = 1mA 100ms/DIV
1695 * G21
1695 * G22
1695 * G23
U
U
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LTC1695
BLOCK DIAGRA
SCL
SDA
W
POWER ON RESET AND UVLO VCC SHUTDOWN CONTROL BOOST START TIMER PULL-DOWN/UP LOGIC THERMAL SHUTDOWN 6-BIT DAC (RESISTORS, SWITCHES) 6 COMMAND REGISTER CURRENT LIMIT VOUT DATA REGISTER R1 50k GND R2 50k
1695 * BD
-
OP AMP P1 0.75
+
SMBus INTERFACE (BUFFERS, LOGIC)
7
LTC1695
SWITCHING WAVEFORMS
Boost Start Timer Measurement ILOAD = 10mA, CLOAD = 4.7F
VOUT = VFS 90% VFS 90% VFS
VOUT = VZS
Output Switch On Time Measurement Code = 63, ILOAD = 1mA, CLOAD = 4.7F fSMBus =100kHz
STOP CONDITION 12 12 13 14 15 COMMAND BYTE D4 D3 D2 16 17 18 19 D5 D1 D0 ACK VOUT = VFS 90% VFS D4 D3 D2 D1 D0 ACK 13 14 15 COMMAND BYTE 16 17 18 19
D5
VOUT = VFS
VOUT = VZS tON
1695 * SW02
8
W
U
VOUT = V(CODE 32) tBST_ST
1695 * SW01
Output Switch Off Time Measurement Code = 0, ILOAD = 150mA, CLOAD = 4.7F fSMBus =100kHz
STOP CONDITION
VOUT = VZS
10% VFS tOFF
1695 * SW03
LTC1695 TI I G DIAGRA W
Operating Sequence
S SCL 1 2 3 4 5 6 SLAVE ADDRESS 0 1 0 7 8 9 10 11 12 13 14 15 COMMAND BYTE D4 D3 D2 16 17 18 19 SMBus SEND BYTE PROTOCOL, WITH SMBus ADDRESS = 1110100B P 1 1 0 WR ACK X BST D5 D1 D0 ACK SMBus RECEIVE BYTE PROTOCOL, WITH SMBus ADDRESS = 1110100B P 2 3 4 5 6 SLAVE ADDRESS 0 1 0 7 8 9 10 11 12 13 14 15 COMMAND BYTE 0 0 0 16 17 18 19 1 1 0 WR ACK OCF THE 0 0 0 ACK
1695 * TD01
UW
SDA
1
S = SMBus START BIT P = SMBus STOP BIT BST = 1 ENABLES THE BOOST START TIMER D5 TO D0 = 6-BIT INPUT CODE FOR THE DAC (D5 = MSB) X = DON'T CARE
S SCL 1
SDA
1
S = SMBus START BIT P = SMBus STOP BIT OCF = 1 SIGNALS THAT THE LTC1695 IS IN CURRENT LIMIT THE = 1 SIGNALS THAT THE LTC1695 IS IN THERMAL SHUTDOWN
Timing for SMBus Interface
STOP START tBUF SDA tHD(STA) SCL tLOW tHIGH tHD(DAT) tSU(STA) tSU(DAT) tSU(STO)
1695 * TD02
START
STOP
tr
tf
tHD(STA)
9
LTC1695
DEFINITIONS
Resolution: The number of DAC output states (2N) that divide the full-scale range. The resolution does not imply linearity. Full-Scale Voltage (VFS): The regulator output voltage (VOUT) if all DAC bits are set to ones (code 63). Voltage Offset Error (VOS): The regulator output voltage if all DAC bits are set to zeros. The LDO amplifier can have a true negative offset, but due to the LTC1695's single supply operation, VOUT cannot go below ground. If the offset is negative, VOUT will remain near 0V resulting in the transfer curve shown in Figure 1.
Table 1. Nominal VLSB and VFS values VCC VLSB
4.5V 5.0V 5.5V 70.3mV 78.1mV 85.9mV
VFS
4.430V 4.922V 5.414V
INL: Integral nonlinearity is the maximum deviation from a straight line passing through the endpoints of the DAC transfer curve. Due to the LTC1695's single supply operation and the fact that VOUT cannot go below ground, linearity is measured between full scale and the first code (code 01) that guarantees a positive output. The INL error at a given input code is calculated as follows: INL = (VOUT - VIDEAL))/VLSB VIDEAL = (Code * VLSB) + VOS
OUTPUT VOLTAGE NEGATIVE OFFSET 0V
VOUT = The output voltage of the DAC measured at the given input code
DAC CODE
1695 * F01
Figure 1. Effect of Negative Offset
DNL: Differential nonlinearity is the difference between the measured change and the ideal 1LSB change between any two adjacent codes. The DNL error between any two codes is calculated as below: DNL = (VOUT - VLSB)/VLSB VOUT = The measured voltage difference between two adjacent codes The VOUT calculation includes the VOS values to account for the effect of negative offset in Figure 1. This is relevant for code 1's DNL.
The offset of the part is measured at the first code (code 1) that produces an output voltage 0.5LSB greater than the previous code. VOS = VOUT - [(Code * VFS)/(2N - 1)] Least Significant Bit (VLSB): The least significant bit or the ideal voltage difference between two successive codes. VLSB = (VFS - VOS)/(2N - 1)
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LTC1695
APPLICATIONS INFORMATION
OVERVIEW The LTC1695 is a 5V brushless DC fan speed controller. Fan speed is controlled by linear regulating the applied voltage to the fan. To program fan speed, a system controller or microprocessor first sends a 6-bit digital code to the LTC1695 via a 2-wire SMBus/I2C interface. The LTC1695's DAC then converts this digital code into a voltage reference. Finally, the LTC1695's op amp loop regulates the gate bias of the internal P-channel pass transistor to control the corresponding output voltage. The LTC1695 is designed for portable, power-conscious systems that utilize small 5V brushless DC fans. These fans are increasingly popular in providing efficient cooling solutions in a small footprint. Smaller fans allow a user to employ multiple fans at strategic physical locations to govern a system's thermal airflow ("air duct" concept). These brushless DC fans also make use of the 5V supply used by the main digital/analog circuitry, removing the need for a 12V supply required by higher power fans. The LTC1695's P-channel linear regulator control approach offers the lowest solution component count, the smallest PCB board space consumed, wide fan speed control range and low acoustical/electrical generated noise. Thermal concerns over the use of a linear regulator topology are eliminated by the fan's generally resistive behavior. As the LTC1695 DAC codes are changed to lower the output voltage, the voltage across the internal P-channel pass transistor increases. However, the fan's load current decreases almost linearly, thereby controlling power dissipation in the regulator. For example, a Micronel 5V, 0.7W fan (40mm2 * 12mm) draws 80mA at 4V and 20mA at 2V. Thus the P-channel pass transistor's power loss decreases from 80mW to 60mW. The LTC1695 incorporates several features to simplify the overall solution including a boost start timer to ensure fan start-up, output current limiting and thermal shutdown. The boost start timer is enabled via the SMBus commands and programs VOUT to full scale for 250ms before regulating at the user programmed output voltage. This eliminates potential fan start-up problems at lower output voltage DAC codes. The LTC1695's thermal shutdown circuit trips if die temperature exceeds 155C. The P-channel pass transistor is shut off and bit D6 in the LTC1695's SMBus data register is set high. If an overload or short-circuit condition occurs, the LTC1695's current-limit circuitry limits output current to 390mA typically. In addition, bit D7 in the SMBus data register is set high. The readback capability of the LTC1695 allows the host controller to monitor the status of the D6 and D7 bits for fault conditions. SMBus Serial Interface The LTC1695 is an SMBus slave device that supports both SMBus send byte and receive byte protocol (Figure 2) with two interface signals, SCL and SDA. The SMBus host initiates communication with the LTC1695 through a start bit followed by a 7-bit address code and a write bit. Each SMBus slave device in the system compares the address code with its specific address. For send byte and receive byte protocol, the write bit is LOW and HIGH respectively. If selected, the LTC1695 acknowledges by pulling SDA low. If send byte protocol is used, the host issues an 8-bit command code. After receiving the entire command byte, the LTC1695 again acknowledges by pulling SDA low. At the falling edge of the acknowledge pulse, the LTC1695's DAC latches in the new command byte from its shift register. If receive byte protocol is used, the LTC1695 acknowledges by pulling SDA low after the write bit. The LTC1695 then transmits the data byte. After the host receives the entire data byte, the cycle is terminated by a "NOT Acknowledge" bit and a stop bit.
U
W
U
U
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LTC1695
APPLICATIONS INFORMATION
SMBus SEND BYTE PROTOCOL 1 S 1 2 1 3 1 4 0 5 1 6 0 7 0 8 0 9 0 A 10 11 12 13 14 15 16 17 18 19 X BST D5 D4 D3 D2 D1 D0 0 MSB LSB A STOP P
A6 A5 A4 A3 A2 A1 A0 W START
SLAVE ADDRESS
COMMAND BYTE
SMBus RECEIVE BYTE PROTOCOL 1 S 1 2 1 3 1 4 0 5 1 6 0 7 0 8 1 9 10 11 12 13 14 15 16 17 18 19 0 0 0 0 0 1 A STOP P 0 OCF THE 0 A
A6 A5 A4 A3 A2 A1 A0 W START
SLAVE ADDRESS
DATA BYTE
S = SMBus START BIT P = SMBus STOP BIT BST = 1 ENABLES THE BOOST START TIMER D5 TO D0 = 6-BIT INPUT CODE FOR THE DAC (D5 = MSB) OCF = 1 SIGNALS THAT THE LTC1695 IS IN CURRENT LIMIT THE = 1 SIGNALS THAT THE LTC1695 IS IN THERMAL SHUTDOWN BIT 18 = 1 IS A NOT ACKNOWLEDGE FOR RECEIVE BYTE PROTOCOL NOTE: DURING POWER UP AND UVLO, DAC INPUT BITS (D5 TO D0) AND THE BST BIT ARE RESET TO ZERO 1695 * F02
Figure 2. SMBus Interface Bit Definition
SCL and SDA SCL is the synchronizing clock signal generated by the host. SDA is the bidirectional data transfer line between the host and a slave device. The host initiates a start bit by pulling SDA from high to low while SCL is high. The stop bit is initiated by changing SDA from low to high while SCL is high. All address, command and acknowledge signals must be valid and should not change while SCL is high. The acknowledge bit signals to the host the acceptance of a correct address byte or command byte. The SCL and SDA input threshold voltages are typically 1.4V with 40mV of hysteresis. Connect the SCL and SDA open-drain lines to either a resistive or current source pull up. The LTC1695 SDA has an open-drain N-channel tran-
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W
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U
sistor capable of sinking 3mA at less than 0.4V during the slave acknowledge sequence. The LTC1695 is compatible with the Philips/Signetics I2C Bus Interface. The 1.4V threshold for SCL and SDA does not create any I2C application problems. Early Stop Conditions If a stop condition occurs before the data byte is acknowledged in the write byte protocol, the LTC1695's DAC is not updated. Otherwise, the internal register is updated with the new data and VOUT changes accordingly to the new programmed value. Address, Command, Data Selection The LTC1695's address is hard-wired internally as 1110100 (MSB to LSB, A6 to A0). Consult LTC for parts with alternate address codes. Consult the Address, Command and Data Byte Tables for further information and as a concise reference. As shown in Figure 2, D5 to D0 in the command code, control the linear regulator's output voltage and thus fan speed. D5 to D0 are sent from the host to the LTC1695 during send byte protocol. The LTC1695 latches D5 to D0 as DAC input data at the falling edge of the data acknowledge signal. The host must set "BST" (boost start enable bit) to high if the LTC1695's 250ms boost start timer option is used. All bits are reset to zero during power-on reset and UVLO. As shown in the Timing Diagram, bit 6 and bit 7 in the data byte register are defined as thermal shutdown status (THE) and over current fault (OCF) status respectively. The LTC1695 sets OCF high if ILOAD exceeds 390mA typically and "THE" high if junction temperature exceeds 155C typically. The remaining bits of the data byte's register (bit 5 to 0) are set low during host read back.
LTC1695
APPLICATIONS INFORMATION
VCC VCC/2
64 RESISTOR VOLTAGE TABS
720 SWITCHES
REFERENCE OP AMP "000000" = 0V "111111" = 0.984 * VCC/2
GND
6 SMBus COMMAND D5 to D0
Figure 3. Ladder DAC
DAC The LTC1695 uses a 128-segment resistor ladder to implement the monotonic 6-bit voltage DAC (Figure 3). Guaranteeing monotonicity (no missing codes) permits the use of the LTC1695 in thermal feedback control applications. As the typical application uses a 5V supply for VCC, the reference for the 6-bit DAC is VCC. LTC recommends a 10F or greater tantalum capacitor to bypass VCC. Users must account for the variation in the DAC's output absolute accuracy as VCC varies. VCC voltage should not exceed the absolute maximum rating of 7V or drop below the typical 2.8V undervoltage lockout threshold (UVLO) during normal operation. The LTC1695's DAC specifications (INL, DNL, VOS) account for the offset and gain errors of the linear regulator with respect to ILOAD. Consult the Definitions section for more details. The worst-case condition occurs if the LTC1695 P-channel pass transistor enters dropout at full-scale VOUT and ILOAD. Full-scale VOUT (VFS) is 4.922V with VCC = 5V. In this condition, loop gain drops and gain error increases. The LTC1695 is designed for monotonicity up to VFS with DNL and INL less than 0.75 LSB. Refer to the Electrical Characteristics and Typical Performance Characteristics for more information.
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Linear Regulator Loop Compensation The LTC1695's linear regulator approach is a simple and practical scheme for fan speed control featuring a wide and linear dynamic range. It also introduces less noise into the system supply rail, compared with a PWM scheme (fixed frequency, variable duty cycle), switching regulator topology or simple ON-OFF control. The LTC1695 linear regulator feedback loop requires a capacitor at its output to stabilize the loop over the output voltage and load current range. The output capacitor value and the capacitor's ESR value are critical in stabilizing the LTC1695 feedback loop. A 1F general purpose, low to medium ESR (0.1 to 5) tantalum or aluminium electrolytic capacitor is sufficient for most applications. These capacitor types offer a lowcost advantage, particularly for fan speed control applications. As the output capacitance value increases, stability improves. A typical 4.7F, 1 ESR surface mount tantalum capacitor is recommended for the optimum transient response and frequency stability across temperature, VOUT and ILOAD. Refer to the load transient response waveforms in the Typical Performance Characteristics section. The selection of the capacitor for COUT must be evaluated by the user for temperature variation of the capacitance and ESR value and the voltage coefficient of the capacitor value. For example, the ESR of aluminium electrolytic capacitors can increase dramatically at cold temperature. Therefore, the regulator may be stable at room temperature but oscillate at cold temperature. Ceramic capacitors with Z5U and Y5 dielectrics provide high capacitance values in a small package, but exhibit strong voltage and temperature coefficients (-80% in some cases). In addition, the ESR of surface mount ceramic capacitors is too low (<0.1) to provide adequate phase-lead in the feedback loop for stability. Fan Load and CLOAD Referring to Figure 4, CLOAD varies greatly depending on the type of fan used. The simplest, inexpensive fans contain no protection circuitry and input capacitance is on the order of 200pF. More expensive fans generally incorporate a series-diode for reverse protection and input
1695 * F03
13
LTC1695
APPLICATIONS INFORMATION
VCC INTERNAL DAC OUTPUT
-
OP AMP P1(0.75)
+ +
CNODE
CGATE
+
VOUT
EQUIVALENT DC FAN CIRCUIT
R1 LFAN ESR CFAN R2 COUT GND
1695 * F04
+
Figure 4. Regulator Feedback Loop
capacitance ranges from 2pF to 30pF. As previously discussed, an output bypass capacitor is required to stabilize the feedback loop. This output capacitor is in parallel with the fan's input capacitance and dominates the total capacitance. Thus, stability is generally not affected by the fan's input capacitance. The output capacitor also serves to filter the fan's output ripple during commutation of the fan's motor. POR and UVLO Under start-up conditions, the LTC1695 performs a power on reset (POR) function. The digital logic circuitry is disabled and the regulator is held off. The SMBus command register (to the DAC's input) and data register (current limit and thermal shutdown status) are reset to zero. The POR signal deactivates if VCC rises above 2.9V typically. The LTC1695 is then allowed to communicate with the SMBus host and drive the fan accordingly. Upon exiting POR, the regulator's output voltage is set to VZS (code 0) until programmed by the SMBus host. The LTC1695 enters UVLO if VCC falls below 2.8V typically. Between 2.8V and 1V, the digital logic circuitry is disabled, the command/data registers are cleared and the regulator is shut down. In general, 100mV of hysteresis exists between the UVLO and POR thresholds.
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Thermal Considerations The LTC1695's power handling capability is limited by the maximum rated junction temperature of 125C. Power dissipation (PDISS) consists of two components: 1. Output current multiplied by the input/output voltage differential: (ILOAD)(VCC - VOUT), and 2. GND pin current multiplied by the input voltage: (IGND)(VCC). PDISS = (ILOAD)(VCC - VOUT) + (IGND)(VCC) TJ = PDISS * (JA) The LTC1695 has active current limiting and thermal shutdown circuitry for device protection during overload or fault condition. For continuous overload conditions, do not exceed the 125C maximum junction temperature TJ(MAX). Give careful consideration to all thermal resistance sources from junction to ambient. Consider any additional heat sources mounted in proximity to the LTC1695. This is particularly relevant in applications where the LTC1695's output is loaded with a constant ILOAD and VOUT is dynamically varied via the SMBus. At lower DAC output voltage codes, the increased input-tooutput differential increases power dissipation if ILOAD does not decrease. For the LTC1695's 5-lead SOT-23 surface mount package, heat sinking is accomplished by using the heat spreading capabilities of the PC board and its copper traces (in particular, the GND pin trace). The following table lists measured thermal resistance results for various size boards and copper areas. All measurements were taken in still air on 3/32" FR-4 board with one ounce copper.
Table 2. Measured Thermal Resistance (JA) Copper Area Thermal Resistance Topside* Backside Board Area (Junction to Ambient)
2500mm2 1000mm2 225mm2 100mm2 50mm2 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 125C/W 125C/W 130C/W 135C/W 150C/W
+
*Device is mounted on topside
LTC1695
APPLICATIONS INFORMATION
For further information, refer to the Junction Temperature Increase (above ambient temperature) vs ILOAD graph in the Typical Performance Characteristics section. This graph provides a fast and simple junction temperature estimation with various VOUT (DAC code) and ILOAD combinations for a typical application. Boost Start Timer In general, a 5V brushless DC fan starts at a voltage value higher than the voltage at which it stalls. This behavior is directly attributed to the force necessary to overcome the back EMF of the fan. For example, one fan measured started at 3.5V but operated until its terminal voltage fell below 2.1V. Therefore, users must ensure start-up in the fan before programming the fan voltage to a value lower than the starting voltage. Monitoring the fan's DC current for a stalled condition does not work due to the fan's resistive nature. Fans can sink load current even though they are not rotating. Other approaches include detecting absence of the fan's commutation ripple current and tachometers. In general, these approaches are more complex, require more circuitry, add cost and have to be customized for the specific fan used. The LTC1695 contains a programmable boost start timer offering three flexible solutions to the user: 1.) Enable the boost start timer bit (D6 in the DAC command code). Each time a new output voltage is programmed, the timer forces VOUT to full scale (4.922V nominal with VCC = 5V) for 250ms before assuming the programmed output voltage value. This ensures fan start up even if the programmed output voltage is below the fan's start threshold. 2.) Users may also choose to use a software timer routine inside the host controller to power the DC fan, at full scale, for a programmed time period before programming VOUT to a lower desired DAC output voltage code. 3.) Users may choose a tachometer fan that feedbacks its speed to the SMBus host. If fan stall conditions are detected, the SMBus host re-programs the LTC1695. Beyond a typical 125C LTC1695 junction temperature, the boost start timer (if activated) maintains VOUT at full Thermal Shutdown, Overcurrent The LTC1695 shuts down the P-channel linear regulator if die temperature exceeds 155C typically. The thermal shutdown circuitry employs about 30C of hysteresis. As previously mentioned, the LTC1695 sets bit 6 (THE) in the SMBus data byte register HIGH during thermal shutdown conditions. During a fault condition, the LTC1695's SMBus logic continues to operate so that the SMBus host can read back the fault status data. During an overload or short-circuit fault condition, the LTC1695's current-limit detector sets bit 7 (OCF) in the SMBus data byte register HIGH and actively limits output current to 390mA typically. This protects the LTC1695's P-channel pass transistor. Under dead short conditions with VOUT = 0V, the LTC1695 also clamps the output current. However, the increased power dissipation (5V * 390mA = 1.95W) eventually forces the LTC1695 into thermal shutdown. The LTC1695 will then thermally oscillate until the fault condition is removed. During recovery from thermal shutdown (typically 125C), the LTC1695 automatically activates the boost start timer, programming the fan voltage to full scale for 250ms (TBST_ST), before switching to the user programmed output voltage value. This again eliminates fan start-up problems if the thermal shutdown fault occurred while the fan was previously operating at an output voltage below the fan's starting voltage. In addition, as discussed, the boost start timer will keep VOUT at VFS for an extended time period beyond TBST_ST until the LTC1695's junction temperature drops below 105C. The LTC1695's protection features protect itself, the fan, and more importantly alerts the SMBus host to any system thermal management fault conditions. scale (VFS) until junction temperature decreases to approximately 105C. This extended timer period is an attempt to cool down the system and the LTC1695 by running the fan at full speed. In most cases, such elevated ambient temperatures require the fan to run at full speed anyway. The remaining LTC1695's functionality remains unchanged.
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LTC1695
APPLICATIONS INFORMATION
DC FAN SELECTION The LTC1695, in the 5-lead SOT-23 package, caters mainly to 5V brushless DC fans, in spot cooling and notebook computer applications, that consume less than 1W maximum. These applications typically require fan footprints on the order of 4000mm3 to 20000mm3. Such fan sizes are common and commercially available. Examples of these miniature fans are the "Ultra-thin DC fan" and "Extra-mini DC fan" from SUNON Inc. Models in these series range from 17mm to 40mm in size, weigh from 4 grams to 10 grams and provides airflow densities from 0.65 CFM to 6 CFM. Users must consider parameters like physical size (L * W * H), airflow (CFM), power dissipation (W) and acoustically generated noise (dBA) when choosing a fan. Users must also evaluate the fan's I-V characteristics versus fan speed and the start/stall characteristics of the fan. Other factors include mechanical considerations such as low cost sleeve bearings or ball bearings that have better long term reliability. Finally, users must consider if the fan requires any input protection features such as reverse-voltage protection. All of these factors affect the fan's cost. Table 3 lists some 5V fan manufacturer's contact information.
Table 3. 5V DC Fan Manufacturers Manufacturer Address
SUNON Inc. 1075 W. Lambert Rd., Brea, CA 92821 Tel: (714)255-0208 Website: http://www.sunon.com 1280 Liberty Way, Vista, CA 92083 Tel: (760)727-7430 152 Will Dr., Canton, MA 02021 Tel: (781)828-6216 Website: http://nidec.com
CURRENT (mA)
Advanced Technology Company Nidec America
NMB Technologies Inc. 9730 Independence Ave., Chatsworth, CA 91311 Tel: (818)341-3355 Website: http://www.nmbtech.com Micronel 1280 Liberty Way, Vista, CA 92083 Tel: (760)727-7400 Website: http://www.micronel.com
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Table 4 lists some 5V brushless DC fans suitable for typical LTC1695 fan speed control applications. Figure 5 shows the measured I-V characteristics of these fans. For a particular fan selection, users must determine the minimum DAC output voltage code below which the fan stalls. Most fans continue to consume current, even in a stalled condition.
Table 4. Some 5V DC Fans' Characteristics Manufacturer Part Number Airflow Power Size (CFM) (W) (L * W * H)mm3
SUNON ATC SUNON SUNON SUNON Micronel KDE0501PFB2-8 AD0205HB-G51 KDE0502PFB2-8 KDE0503PFB2-8 KDE0535PFB2-8 F41MM-005XK-9 0.65 0.80 1.70 3.20 4.80 6.10 0.50 0.45 0.60 0.60 0.70 0.70 20 * 20 * 10 25 * 25 * 10 25 * 25 * 10 30 * 30 * 10 35 * 35 * 10 40 * 40 * 12
150 125 100 75 50 25
KDE0501PFB2-8 KDE0535PFB2-8 KDE0502PFB2-8 AD0205HB-G51 KDE0503PFB2-8 F41MM-005XK-9
TA = 25C 0 0 1 2 3 4 TERMINAL VOLTAGE (V) 5
1695 * F05
Figure 5. I-V Characteristics of 5V Brushless DC Fan Samples
LTC1695
APPLICATIONS INFORMATION
SMBus Address Byte Table
Decimal 232 233 HEX E8 E9 SMBus Protocol Send Byte to the LTC1695 Receive Byte from the LTC1695 0 128 64
The LSB of the SMBus address is the write bit. For send byte protocol, W = 0. For Receive byte protocol, W = 1
SMBus Command Byte Table (Send Byte Protocol)
DECIMAL (D5 to D0) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 BINARY MSB LSB X0000000 X0000001 X0000010 X0000011 X0000100 X0000101 X0000110 X0000111 X0001000 X0001001 X0001010 X0001011 X0001100 X0001101 X0001110 X0001111 X0010000 X0010001 X0010010 X0010011 X0010100 X0010101 X0010110 X0010111 X0011000 X0011001 X0011010 X0011011 X0011100 X0011101 X0011110 X0011111 HEX (D6-D7 set to 0) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F Nominal VOUT(V) ILOAD = 1mA 0.000 0.078 0.156 0.234 0.313 0.391 0.469 0.547 0.625 0.703 0.781 0.859 0.938 1.016 1.094 1.172 1.250 1.328 1.406 1.484 1.563 1.641 1.719 1.797 1.875 1.953 2.031 2.109 2.188 2.266 2.344 2.422 DECIMAL (D5 to D0) 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 BINARY MSB LSB X0100000 X0100001 X0100010 X0100011 X0100100 X0100101 X0100110 X0100111 X0101000 X0101001 X0101010 X0101011 X0101100 X0101101 X0101110 X0101111 X0110000 X0110001 X0110010 X0110011 X0110100 X0110101 X0110110 X0110111 X0111000 X0111001 X0111010 X0111011 X0111100 X0111101 X0111110 X0111111 HEX (D6-D7 set to 0) 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F Nominal VOUT(V) ILOAD = 1mA 2.500 2.578 2.656 2.734 2.813 2.891 2.969 3.047 3.125 3.203 3.281 3.359 3.438 3.516 3.594 3.672 3.750 3.828 3.906 3.984 4.063 4.141 4.219 4.297 4.375 4.453 4.531 4.609 4.688 4.766 4.844 4.922
D6 = 0 disables the boost start timer. D7 = X = don't care
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SMBus Data Byte Table (Receive Byte Protocol)
DECIMAL BINARY MSB LSB 00000000 10000000 01000000 HEX 00 80 40 LTC1695 Status No Fault Overcurrent Fault/Clamp Thermal Shutdown
During thermal shutdown, the LTC1695's LDO is shut off.
D6 = 0 disables the boost start timer. D7 = X = don't care
17
LTC1695
APPLICATIONS INFORMATION
SMBus Command Byte Table (Boost Start Timer Enabled)
DECIMAL (D5 to D0) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 BINARY MSB LSB X1000000 X1000001 X1000010 X1000011 X1000100 X1000101 X1000110 X1000111 X1001000 X1001001 X1001010 X1001011 X1001100 X1001101 X1001110 X1001111 X1010000 X1010001 X1010010 X1010011 X1010100 X1010101 X1010110 X1010111 X1011000 X1011001 X1011010 X1011011 X1011100 X1011101 X1011110 X1011111 HEX (D7 set to 0) 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F 50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5F Nominal VOUT(V) LOAD = 1mA 0.000 0.078 0.156 0.234 0.313 0.391 0.469 0.547 0.625 0.703 0.781 0.859 0.938 1.016 1.094 1.172 1.250 1.328 1.406 1.484 1.563 1.641 1.719 1.797 1.875 1.953 2.031 2.109 2.188 2.266 2.344 2.422 DECIMAL (D5 to D0) 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 BINARY MSB LSB X1100000 X1100001 X1100010 X1100011 X1100100 X1100101 X1100110 X1100111 X1101000 X1101001 X1101010 X1101011 X1101100 X1101101 X1101110 X1101111 X1110000 X1110001 X1110010 X1110011 X1110100 X1110101 X1110110 X1110111 X1111000 X1111001 X1111010 X1111011 X1111100 X1111101 X1111110 X1111111 HEX (D7 set to 0) 60 61 62 63 64 65 66 67 68 69 6A 6B 6C 6D 6E 6F 70 71 72 73 74 75 76 77 78 79 7A 7B 7C 7D 7E 7F Nominal VOUT(V) ILOAD = 1mA 2.500 2.578 2.656 2.734 2.813 2.891 2.969 3.047 3.125 3.203 3.281 3.359 3.438 3.516 3.594 3.672 3.750 3.828 3.906 3.984 4.063 4.141 4.219 4.297 4.375 4.453 4.531 4.609 4.688 4.766 4.844 4.922
D6 = 1 enables the boost start timer. D7 = X = don't care
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D6 = 1 enables the boost start timer. D7 = X = don't care
LTC1695
PACKAGE DESCRIPTIO
0.35 - 0.55 (0.014 - 0.022)
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DIMENSIONS ARE INCLUSIVE OF PLATING 3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 4. MOLD FLASH SHALL NOT EXCEED 0.254mm 5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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Dimensions in inches (millimeters) unless otherwise noted. S5 Package 5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.80 - 3.00 (0.110 - 0.118) (NOTE 3)
2.60 - 3.00 (0.102 - 0.118) 1.50 - 1.75 (0.059 - 0.069)
1.90 (0.074) REF 0.00 - 0.15 (0.00 - 0.006)
0.95 (0.037) REF
0.90 - 1.45 (0.035 - 0.057)
0.09 - 0.20 (0.004 - 0.008) (NOTE 2)
0.35 - 0.50 0.90 - 1.30 (0.014 - 0.020) (0.035 - 0.051) FIVE PLACES (NOTE 2) S5 SOT-23 0599
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LTC1695
TYPICAL APPLICATION
SMBus I2C Controlled White LED Driver
5V 1 C1 10F 6.3V LTC1695 VCC VOUT 5 C2 + 10F 10V SDA 4 R1 100 LED1 R2 100 LED2 R3 100 LED3 R4 100 LED4 R5 100 LED5 R6 100 LED6
+
2
SCL TO C SDA
3
LED CURRENT (mA)
RELATED PARTS
PART NUMBER LT1120 LT1121 LTC1380/LTC1393 LTC1427-50 LT1521 LTC1623 LTC1663 LTC1694/LTC1694-1 LT1761 LT1762 LT1786F DESCRIPTION 125mA Low Dropout PNP Linear Regulator with 40A Quiescent Current 150mA Low Dropout PNP Linear Regulator with 30A Quiescent Current Single-Ended 8-Channel/Differential 4-Channel Analog Mux with SMBus Interface Micropower, 10-Bit Current Output DAC with SMBus Interface 300mA Low Dropout PNP Linear Regulator with 12A Quiescent Current Dual High Side Switch Controller with SMBus Interface SMBus Interface 10-Bit Rail-to-Rail Micropower DAC SMBus Accelerator 100mA, Low Noise, LDO Micropower Regulator 150mA, Low Noise, LDO Micropower Regulator SMBus Controlled CCFL Switching Regulator COMMENTS 0.6V Dropout Voltage at 125mA 0.5V Dropout Voltage at 150mA, SO8/SOT-223 package Low RON: 35 Single-Ended/70 Differential, Expandable to 32 Single or 16 Differential Channels Precision 50A 2.5% Tolerance Over Temperature, 4 Selectable SMBus Addresses, DAC Powers up at Zero or Midscale 0.5V Dropout Voltage at 150mA, SO8/SOT-223 Package 8 Selectable Addresses/16-Channel Capability DNL < 0.75LBS Max, 5-Lead SOT-23 Package Improved SMBus/I2C Rise Time, Ensures Data Integrity with Multiple SMBus/I2C Devices 0.3V Dropout Voltage at 100mA, SOT-23 Package 0.3V Dropout Voltage at 150mA, MSOP Package 1.25A, 200kHz, Floating or Grounded Lamp Configurations
1695f LT/TP 0400 4K * PRINTED IN USA
20
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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GND
SCL
LED = Hewlett Packard HLMP-CW30 C2 = SPRAGUE 595D106X0010A2T
1695 * TA03a
Output Voltage vs LED Current
20 18 16 14 12 10 8 6 4 2 0 VFS 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT VOLTAGE (V)
1695 * TA03b
(c) LINEAR TECHNOLOGY CORPORATION 2000

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