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PRODUCT DATASHEET
AAT1271
SwitchRegTM
General Description
The AAT1271 is a high-efficiency, high-current boost converter capable of 1.5A typical output current. It is an ideal power solution for LED photo flash applications in all single cell Li-ion powered products. The AAT1271 maintains output current regulation by switching the internal high-side and low-side switch transistors. The transistor switches are pulse-width modulated at a fixed frequency of 2MHz. The high switching frequency allows the use of a small inductor and output capacitor, making the AAT1271 ideally suited for small battery-powered applications. AnalogicTech's proprietary AS2CwireTM (Advanced Simple Serial ControlTM) serial digital interface is used to enable, disable, configure, and program the operation of the AAT1271. Using the AS2Cwire interface, the movie-mode current level for each LED, the safety timer delay, and the flash-to-movie-mode current ratio can be programmed to one of 16 levels. In addition, the single-wire serial protocol sets output channel control. The AAT1271 also includes a separate Flash Enable input to initiate both the flash operation and the default timer which can be used either to terminate a flash event at the end of a userprogrammed delay or as a safety feature. Also included is a Flash Inhibit pin which reduces the flash current to movie-mode levels during high battery demand. The maximum flash and movie-mode current is set by one external resistor where the ratio of Flash to Movie-mode current is set at approximately 7.3:1. One or two LEDs can be connected to the AAT1271, where in the case of two LEDs the output current is matched between each diode. The AAT1271 contains a thermal management system to protect the device in the event of an output short-circuit condition. Built-in circuitry prevents excessive inrush current during start-up. The shutdown feature reduces quiescent current to less than 1.0A. The AAT1271 is available in a Pb-free, thermally-enhanced 14-pin 3x3mm TDFN package.
1.5A Step-Up Current Regulator for Flash LEDs
Features
* VIN Range: 2.7V to 5.5V * Dual Channel Output * Up to 1.5A Regulated Output Current (750mA per channel) * Up to 85% Efficiency with Small Inductor (1H) * 2 MHz Switching Frequency * Separate Flash Enable * Separate Flash Inhibit * User-Programmable Safety Timer * Single Resistor Sets Flash and Movie Mode Current * AS2Cwire Single Wire Programming: Movie Mode Current Flash/Movie Mode Current Ratio Movie Mode Output Configuration Flash Safety Timer * True Load Disconnect * Input Current Limit * Over-Voltage (Open LED, Open Circuit), Short Circuit, and Over-Temperature Protection * Shutdown Current < 1.0A * 14-pin TDFN 3x3 mm Package * -40C to +85C Temperature Range
Applications
* * * * * Camcorder Video Light (Torch Light) Cellphones/Smartphones Digital Still Cameras (DSCs) LED Photo Flash/Torch Mobile Handsets
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Typical Application
L1 1H High Current Flash LEDs OUT VBAT CIN 2.2F
1.5A Step-Up Current Regulator for Flash LEDs
IN
SW
AAT1271
Movie-mode Enable and Set Flash Enable Flash Inhibit FLOUTA FLEN FLOUTB FLINH CT RSET GND AGND PGND FLGND EN/SET
COUT 2.2F
CT
RSET 107k
Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 9 10
Symbol
CT EN/SET FLEN AGND IN SW PGND OUT GND FLINH
Function
Flash timer control input. Connect a capacitor between CT and AGND to set maximum duration of the flash pulse. To disable the flash timer, connect CT to AGND. Enable and Serial Control input. EN/SET is the AS2Cwire addressing and programming input to: a) adjust the movie-mode current level; b) program the flash timer based on CT; c) select the Flash-to-Movie-mode ratio; and d) select FLOUTA and FLOUTB's output configuration. Flash enable pin. A low-to-high transition on the FLEN pin initiates a flash pulse and starts the flash timer. Analog ground pin. Connect AGND to PGND, GND, and FLGND at a single point as close to the AAT1271 as possible. Power input. Connect IN to the input power supply voltage. Connect a 2.2F or larger ceramic capacitor from IN to PGND as close as possible to the AAT1271 Boost converter switching node. Connect a 1H inductor between SW and IN. Power ground pin. Connect PGND to AGND, GND, and FLGND at a single point as close to the AAT1271 as possible. Power output of the boost converter. Connect a 2.2F or larger ceramic capacitor from OUT to PGND as close as possible to the AAT1271. Connect OUT to the anode(s) of the Flash LED(s). Ground pin. Connect GND to PGND, AGND, and FLGND at a single point as close to the AAT1271 as possible. Flash inhibit pin. FLINH is an active HIGH control input with an internal 200k resistor to AGND. A low-tohigh transition on the FLINH pin reduces FLOUTA and FLOUTB output currents to the maximum (default) movie-mode current level for the duration of FLINH. Strobing the FLINH pin low to high does not reset the flash timer. Flash Output B. Connect cathode of Flash LEDB to FLOUTB. For a single flash LED, connect FLOUTB & FLOUTA together. For two flash LEDs, each output will conduct 50% of the total flash output current. Flash ground pin. Connect FLGND to PGND, GND, and AGND at a single point as close to the AAT1271 as possible Flash Output A. Connect cathode of Flash LEDA to FLOUTA. For a single flash LED, connect FLOUTA and FLOUTB together. For two flash LEDs, each output will conduct 50% of the total flash output current. Flash current setting input. A 107k resistor from RSET to AGND sets the maximum flash current available at FLOUTA and FLOUTB to 1.5A. Each FLOUTA and FLOUTB channel will conduct 50% of the maximum programmed current. The AAT1271's flash-to-movie-mode ratio is fixed at 7.3:1. Exposed paddle (bottom); Connect EP to PGND as close as possible to the AAT1271.
11 12 13 14 EP
FLOUTB FLGND FLOUTA RSET
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Pin Configuration
TDFN33-14 (Top View)
1.5A Step-Up Current Regulator for Flash LEDs
CT EN/SET FLEN AGND IN SW PGND
1 2 3 4 5 6 7
14 13 12
EP
11 10 9 8
RSET FLOUTA FLGND FLOUTB FLINH GND OUT
Absolute Maximum Ratings1
(TA = 25C unless otherwise noted.) Symbol
IN, SW, OUT RSET, EN/SET, FLEN, FLINH, CT, FLOUTA, FLOUTB TJ Ts TLEAD
Description
Maximum Rating Maximum Rating Operating Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6.0 VIN + 0.3 -40 to 150 -65 to 150 300
Units
V V C C C
Recommended Operating Conditions
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation
Value
50 2
Units
C/W W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. The AAT1271 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Electrical Characteristics1
VIN = 3.6V; CIN = 2.2F; COUT = 2.2F; L = 1H; RSET = 107k; TA = -40C to 85C, unless otherwise noted. Typical values are TA = 25C. Symbol Description Conditions Min
2.7 EN/SET = FLEN = IN, Set FL Load = 1.5A EN/SET = IN, FLEN = AGND EN/SET = FLEN = FLINH = GND RSET = 107k; FLOUTA + FLOUTB RSET = 107k , Movie Mode Current Set = 100%; FLOUTA + FLOUTB TA = 25C CT = 74nF 0.67 0.23 1.2 1.5 10 206 1.5 2.0 600 140 15 2.5
1.5A Step-Up Current Regulator for Flash LEDs
Typ
Max
5.5 5.5 1 1
Units
V V mA A A % mA MHz ms C C V V
Power Supply Input Voltage Range VIN VOUT(MAX) Maximum Output Voltage IIN(Q) ISHDN(MAX) IFL(TOTAL) IFL(MATCH) IMM(LOAD) Supply Current VIN Shutdown Current Total Output Current, Flash Mode FLOUTA and FLOUTB Current Matching Total Output Current, Movie Mode
fOSC Switching Frequency tDEFAULT Default ON Time Thermal Shutdown Threshold TSD TSD(HYS) Thermal Shutdown Hysteresis EN/SET/ FLEN/ FLINH Logic Control VEN/SET(L), EN/SET, FLEN Input Low Threshold VFLEN(L) VEN/SET(H), EN/SET, FLEN Input High Threshold VFLEN(H) IEN/SET, IFLEN EN/SET or FLEN Input Leakage Current FLINH Input Threshold Voltage VT(FLINH) RIN(FLINH) FLINH Input Resistance to AGND tEN/SET(LOW) EN/SET Serial Interface Low Time tEN/SET(HI_ MIN) Minimum EN/SET high Time tEN/SET(HI_ MAX) Maximum EN/SET High Time tEN/SET(OFF) EN/SET Off Timeout tEN/SET(LAT) EN/SET Latch Timeout tFLEN_ON FLEN ON Delay Time tFLEN_OFF FLEN OFF Delay Time tFLINH_ON FLINH ON Delay Time tFLINH_OFF FLINH OFF Delay Time
0.4 1.4 FLEN/VEN/SET = VIN = 5V -1 1/2VIN 200 0.3 50 75 500 500 EN/SET = GND EN/SET = GND 40 10 93 5 75 1
A V k s ns s s s s s s s
1. The AAT1271 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Typical Characteristics
Efficiency vs. Input Voltage
(Movie and Flash Mode)
85 80
1.5A Step-Up Current Regulator for Flash LEDs
Boost Switching Frequency vs. Input Voltage
(Movie Mode; L = 1H) Switching Frequency (MHz)
3 2.5 2 1.5 1 0.5 0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
90
Efficiency (%)
75 70 65 60 55 50 45 40 2.7 3.1 3.5 3.9 4.3 4.7
750mA/ch 102mA/ch 52mA/ch 26mA/ch
85C 25C -40C
5.1
5.5
Input Voltage (V)
Input Voltage (V)
Shutdown Current vs. Input Voltage
(VEN/SET = VFLEN = 0V)
0.03 1000 900 0.025 0.02 0.015 0.01 0.005 0 2.7 3.1 3.5 3.9 4.3 4.7 5.1
Supply Current vs. Input Voltage
(VEN = VFLEN = 3.6V)
Shutdown Current (A)
Supply Current (A)
800 700 600 500 400 300 200 100 0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
25C -40C
5.5
85C 25C -40C
Input Voltage (V)
Input Voltage (V)
Movie Mode Current Matching vs. Temperature
(IFLOUTX = 103mA/Ch; VIN = 3.6V; L = 1H)
120
Movie Mode LED Current Accuracy vs. Input Voltage
(IFLOUTX = 103mA/Channel; L = 1H)
10 8 6 4 2 0 -2 -4 -6 -8 -10 2.7 3.1 3.5 3.9 4.3 4.7
Output Current (mA)
110 105 100 95 90 85 80 -40 -15 10 35 60
FLOUTA FLOUTB
85
Output Current (mA)
115
FLOUTA FLOUTB
5.1 5.5
Temperature (C)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Typical Characteristics
Movie Mode Output Ripple
(IFLOUTX = 103mA/ch; VIN = 3.6V; L = 1H)
1.5A Step-Up Current Regulator for Flash LEDs
Flash Mode Output Ripple
(IFLOUTX = 750mA/ch; VIN = 4V; L = 1H)
VOUT (AC Coupled) (50mV/div) VINDUCTOR (2V/div) IINDUCTOR (100mA/div)
100mA
VOUT (AC Coupled) (50mV/div) VINDUCTOR (2V/div) IINDUCTOR (50mA/div)
1.65A
0V
0V
Time (500ns/div)
Time (200ns/div)
Flash LED Current Matching vs. Temperature
(IFLOUTX = 750mA/Ch; VIN = 4.2V; L = 1H)
800 790 80 70
Flash On Time Delay vs. Input Voltage
(IFLOUTX = 750mA/ch; COUT = 2.2F; L = 1H)
Output Current (mA)
780 770 760 750 740 730 720 710 700 -40 -15 10 35
TFLEN_OND (s)
60 50 40 30 20 10 0
FLOUTA FLOUTB
60 85
-40C 25C 85C
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Temperature (C)
Input Voltage (V)
Flash Timeout Delay vs. CT Capacitor
(IFLOUTX = 750mA/ch; VIN = 3.6V)
1200
Movie Mode Line Transient
(IFLOUTX = 103mA/ch; VIN = 4.2V to 3.6V)
Flash Timeout (ms)
1000 800 600 400 200 0 0
VIN (500mV/div) IFLOUTx (AC Coupled) (50mA/div)
4.2V 3.6V
20
40
60
80
100
120
140
CT Capacitor (nF)
Time (50s/div)
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Typical Characteristics
Flash Turn On Characteristic
(IFLOUTX = 750mA/ch; VIN = 3.6V; L = 1H)
1.5A Step-Up Current Regulator for Flash LEDs
Movie Mode to Flash Turn On Characteristic
(IFLOUTX = 103mA to 750mA/ch; VIN = 3.6V; L = 1H)
VFLEN (5V/div) VOUT (2V/div) VSINK (2V/div) IFLOUTX (1A/div)
0V
0V
VFLEN (2V/div) VOUT (2V/div) VSINK (500mV/div) IFLOUTX (1A/div)
0V 2V
0V
0V
0V
0A
Time (50s/div)
Time (50s/div)
Movie Mode Turn On Characteristic
(IFLOUTX = 103mA/ch; VIN = 3.6V; L = 1H)
Movie Mode Transition Characteristic
(IFLOUTX = 103mA to 188mA/ch; COUT = 0.22F; VIN = 3.6V; L = 1H) VEN/SET (2V/div) VOUT (2V/div) VSINK (500mV/div)
VEN/SET (5V/div) VOUT (2V/div) VSINK (500mV/div) IFLOUTX (100mA/div)
0V
0V
0V
0V
0V
IFLOUTX (100mA/div)
0V
0A
0A
Time (100s/div)
Time (100s/div)
Flash Timeout vs. Temperature
(IFLOUTX = 750mA/ch; VIN = 3.6V; CT = 47nF)
500 1.4 1.3
EN, FLEN High Threshold Voltage vs. Input Voltage
VEN/SET(H), VFLEN(H) (V)
Flash Timeout (ms)
450 400 350 300 250 200 -40 -15 10 35 60 85
1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
85C 25C -40C
Temperature (C)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Typical Characteristics
EN, FLEN Low Threshold Voltage vs. Input Voltage
1.4 1.3 300
1.5A Step-Up Current Regulator for Flash LEDs
EN/SET Off Timeout vs. Input Voltage
VEN/SET(L), VFLEN(L) (V)
1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1
TEN/SET(OFF) (s)
85C 25C -40C
250 200 150 100 50 2.7
85C 25C -40C
3.1 3.5 3.9 4.3 4.7 5.1 5.5
5.5
Input Voltage (V)
Input Voltage (V)
EN/SET Latch Timeout vs. Input Voltage
300 250
TEN/SET(LAT) (s)
85C 25C -40C
200 150 100 50 2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
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1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
Functional Block Diagram
IN
1.5A Step-Up Current Regulator for Flash LEDs
SW
OUT
FLOUTA FLOUTB EN/SET FLEN FLINH 200k Control
RSET
CT
AGND PGND FLGND GND
Functional Description
The AAT1271 is a boost converter with a current regulated output designed to drive high current white LEDs used in camera flash applications. The AAT1271 has two channels to accurately regulate the current flow through two separate white LEDs. There are two basic modes of operation in the AAT1271; a Flash mode controlled by the FLEN pin and the movie mode controlled through the AS2Cwire interface.
The AAT1271 has two LED current sources which share the output current equally. For a single white LED application, the two current sources can be connected together to apply full output current into the LED. In two LED applications, each diode can be connected to its corresponding current source (FLOUTA or FLOUTB) and the output current will be shared. In applications where only one LED is connected to either FLOUTA or FLOUTB, the unused current sink must be directly connected to OUT, thereby disabling that channel. In mobile GSM systems where the phone remains in constant contact with the base station by regular communication, a FLINH pin is provided to prevent both the camera flash and PA transmission pulses from occurring simultaneously. This avoids potential dips to the Li-ion battery voltage below the system's undervoltage lockout threshold (UVLO). During a flash event, strobing the FLINH pin low-to-high reduces the LED current to the default movie-mode current level for the duration of FLINH. Strobing FLINH high-to-low instructs the AAT1271 to revert the flash LED current to its maximum level, assuming that the FLEN pin is still active (HIGH) and the flash timer has not expired.
Flash Mode
A flash pulse is initiated by strobing the FLEN input pin low-to-high, which initiates a flash pulse and also starts the internal timer. The maximum flash current in the AAT1271 is set by an external resistor, RSET, which sets the flash current and the maximum movie-mode current reduced by a factor of 2. The flash timer will terminate the flash current regardless of the status of the FLEN pin. This can be either used as a simple flash timing pulse or can be used as a safety timer in the event of a control logic malfunction to prevent the LED from over-heating. The maximum flash time is determined by an external timing capacitor connected to the CT pin. The flash duration can be set from 50ms up to a maximum of 1s. The AS2Cwire interface allows further adjustment of the flash timer duration. This allows the flash timer duration to be reduced in 16 linear steps from the maximum time set by the timing capacitor. If the safety timer is not needed in the application, it can be disabled by connecting the CT pin directly to AGND.
Movie Mode
The movie mode current level, channel enable, and the flash to maximum movie mode current ratio are set using the AAT1271's AS2Cwire interface at the EN/SET pin. The movie-mode current level can be adjusted in 16 steps using a logarithmic scale where each code is 1dB below the previous code. Channel current outputs (FLOUTA and FLOUTB) in movie-mode can be enabled or
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PRODUCT DATASHEET
AAT1271
SwitchRegTM 1.5A Step-Up Current Regulator for Flash LEDs
voltage automatically recovers when the over-temperature fault condition is removed. disabled individually or together. Lastly, the flash to maximum movie mode current ratio can be set from 1:2 to 1:30 with respect to the maximum programmed flash current. The FLEN signal takes priority over movie-mode operation. Movie mode operation is controlled entirely by the AS2Cwire interface via the EN/SET pin. Address 2 controls the movie mode on and off functions. Using this register either or both of the LED channels can be turned on to the current values set in Address registers 0 and 3. The movie mode is not operational when the FLEN pin is high and the part is in flash mode operation. If the AAT1271 is in movie mode (FLEN=low) and the FLEN is strobed high the movie mode state will end and the part will operate in the flash mode. The part will not reenter movie mode when ENFL is brought low. To reenter movie mode after a flash event the part must be turned off and the AS2Cwire interface must be reprogrammed to the desired movie mode level.
Over-Voltage Protection (Open LED, Open Circuit)
The AAT1271's output voltage is limited by internal overvoltage protection circuitry, which prevents damage to the AAT1271 from open LED or open circuit conditions. During an open circuit, the output voltage rises and reaches 5.5V (typical), and the OVP circuit disables the switching, preventing the output voltage from rising higher. Once the open circuit condition is removed, switching will resume. The controller will return to normal operation and maintain an average output voltage.
Auto-Disable Feature
The AAT1271 is equipped with an auto-disable feature for each LED channel. After the IC is enabled and started up, a test current of 2-3mA (typical) is forced through each sink channel. The channel will be disabled if the voltage of that particular SINK pin does not drop to a certain threshold. This feature is very convenient for disabling an unused channel or during an LED fail-short event. This small test current should be added to the set output current in both Flash and MM conditions.
Over-Temperature Protection
Thermal protection disables the AAT1271 when internal power dissipation becomes excessive, as it disables both MOSFETs. The junction over-temperature threshold is 140C with 15C of temperature hysteresis. The output
Timing Diagram
FLASH FLASH FLASH FLASH FLASH FLASH TIMES OUT
tDLY(CT)
MOVIE MODE
LED CURRENT
NO FLASH
NO FLASH FLASH TIMES OUT SET BY CT
t DLY(CT)
FLASH LOWERED TO DEFAULT MOVIE-MODE DURING FLINH DATA TO MOVIE-MODE LEVEL EN/SET
FLASH ENABLE
FLASH INHIBIT
No AS2C address programming shown.
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Applications Information
LED Selection
The AAT1271 is specifically designed to drive white flash LEDs (typical forward voltage of 2.5V to 4.0V). Since the FLOUTA and FLOUTB input current sinks are matched with low voltage dependence; the LED-to-LED brightness will be matched regardless of the individual LED forward voltage (VF) levels.
1.5A Step-Up Current Regulator for Flash LEDs
AS2Cwire Control of Movie Mode Operation and Flash Safety Timer
In the AAT1271 control of the movie mode operation and flash timer is managed by the Advanced Simple Serial Control (AS2Cwire) interface. AS2Cwire relies on the number of rising edges of the EN/SET pin to address and load the AAT1271's registers. As shown in Table 1, Address 0 controls the Movie Current level as a percentage of the maximum movie mode current level. Address 1 controls the safety timer duration as a percentage of the maximum value set by an external timing capacitor. Address 2 enables the two LED channels independently during movie mode. Finally, Address 3 sets the maximum possible current for movie mode operation. The maximum movie mode current is set as a fraction of the flash current with peak value of 1/2 and default value of 1/7.3. The last column in Table 1 shows the default values for each of the address registers.
Flash Mode LED Current
FLOUTA and FLOUTB can be programmed up to a maximum total flash current of 1.5A or up to 750mA per channel. The output currents in FLOUTA and FLOUTB are equal. The maximum flash current in each FLOUTA and FLOUTB is set by the RSET resistor. For the desired flash current in each output, the resistor value can be calculated using the following equation:
AS2Cwire Serial Interface
AS2Cwire latches data or address after the EN/SET pin has been held high for longer than tLAT (500s). Address or data is differentiated by the number of EN/SET rising edges. Since the data registers are 4 bits each, the differentiating number of pulses is 24 or 16, so that Address 0 is signified by 17 rising edges, Address 1 by 18 rising edges and Address 2 by 19 rising edges and Address 3 by 20 rising edges. Data is applied to any number of rising edges between 1 and 16, inclusive. A typical write protocol is a burst of EN/SET rising edges, signifying a particular address, followed by a pause with EN/SET held high for the prescribed tLAT timeout period, a burst of rising edges signifying data, and a tLAT timeout for the data registers. Once an address is set, then multiple writes to the corresponding data register are allowed. Address 0 is the default address on the first rising edge after the AAT1271 has been disabled.
81k x A 81k x A = = 750mA per channel IFLOUTA = IFLOUTB = RSET 107k
A flash event is initiated by asserting the FLEN pin. A flash event is automatically terminated when FLEN is deasserted or if the safety timer terminates before the FLEN pin is de-asserted. Any time that the FLINH pin is asserted, the default movie-mode current level will appear at both FLOUTA and FLOUTB. The default moviemode current level will be maintained on FLOUTA and FLOUTB as long as the FLINH and FLEN pins are asserted, and the safety timer continues to run. In addition to setting the flash current via RSET, the flash current can be changed after FLEN is asserted by programming the movie mode current register with 16 different steps.
Address
0 1 2 3
EN/SET Rising Edges
17 18 19 20
Function
Movie Mode Current Flash Safety Timer Movie Mode Output Configuration Flash/Movie Mode Current Ratio
Default (No programming)
100% 16/16 FLOUTA and FLOUTB OFF 1/7.3
Table 1: AS2Cwire Serial Interface Addressing.
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PRODUCT DATASHEET
AAT1271
SwitchRegTM 1.5A Step-Up Current Regulator for Flash LEDs
movie mode operation, the maximum current available at either FLOUTA or FLOUTB is then: When EN/SET is strobed low and held low longer than tOFF (500s), the AAT1271 enters shutdown mode and draws less than 1uA from VIN. All data and address are cleared (reset to 0) during shutdown. The AS2Cwire addressing allows the control of the moviemode output current, the safety timer delay, independent control of the FLOUTA and FLOUTB current sinks, and the ratio of movie-mode current to flash current. If there are no programmed write instructions applied to the EN/SET pin prior to the assertion of the FLEN pin and the device is enabled, then all registers will be loaded with their default values shown in Table 1. In the event that the number of rising edges applied at the EN/SET pin is less than 17, the AAT1271's state machine will interpret instruction to program the output currents to the desired current level for movie-mode operation.
IMOVIE MODE[A/B] =
IFLOUT[A/B]MAX 750mA = = 103mA 7.3 7.3
Address 0 controls precise movie mode current levels. The FLOUTA/FLOUTB movie-mode current can be adjusted in logarithmic fashion to one of 16 steps represented as a fraction of the maximum movie mode current in Table 2. To adjust the movie-mode current the user must first access Address 0 before writing the data to set the MM Current value. Data
1* 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Percentage of Maximum MM Current
100% 89% 79% 71% 63% 56% 50% 45% 40% 36% 32% 28% 25% 22% 20% 0%
Movie Mode Current - Address 0
The AAT1271 movie mode current settings are controlled using the AS2Cwire interface. Movie Mode current has a maximum value of 50% of the flash current with 240 possible current levels. The maximum movie mode current is set by Address register 3 (discussed below). The default ratio between the flash current level and maximum movie mode current level is 1:7.3. The corresponding FLOUTA/FLOUTB maximum movie mode current can be calculated:
I IMOVIE MODE[A/B] = FLOUT[A/B]MAX 7.3
For example, if an RSET value of 107k is chosen, then the FLOUTA/FLOUTB flash current is set to 750mA. For
Table 2: Address 0, Movie Mode Current Programming.
Address
T HI T LO TLAT
Data
TLAT
EN/SET
1 2 16 17 1 2... n 16
Address
0
1
Data Reg 1
0
n
Figure 1: AS2CwireTM Serial Interface Timing.
* Denotes the default value.
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1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
Flash/Safety Timer - Address 1
A timer function that enables the flash current sinks for a programmed amount of time is incorporated in the AAT1271. The on-time is programmed by loading the Timing Register at Address 1 with a value from 1 to 16 and by choosing a value for the external timing capacitor, CT (see Table 3). When data is latched into Address 1, the data will be used at the next occurrence of an asserted FLEN, it will then revert back to the default value of Data 1, or 16/16. This feature eliminates the need for an external, housekeeping baseband controller to contain a safety delay routine. It also serves as a protection feature to minimize thermal issues with the Flash LEDs in the event an external controller's flash software routine experience hang-up or freeze. If no write instruction is applied to Address 1, then the safety timer will default to the maximum delay programmed externally at CT. The Flash Time T can be calculated by the following equation:
1.5A Step-Up Current Regulator for Flash LEDs
Data
1* 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Ratio of MM Timeout
16/16 15/16 14/16 13/16 12/16 11/16 10/16 9/16 8/16 7/16 6/16 5/16 4/16 3/16 2/16 1/16
Table 3: Address 1, Flash Safety Timer Programming; Maximum Value Programmed by CT.
T = 7.98s/F * CT (F)
Where T is in seconds and CT is in F. For example, using a 47nF capacitor at CT sets the flash timeout to:
Output Enable Control - Address 2
In the case where two LEDs are used, each output can be enabled or disabled independently in movie mode as shown in Table 4. To enable or disable either or both FLOUTA and FLOUTB, a write instruction to Address 2 is applied to the AAT1271's EN/SET pin. If no write instruction is applied, the default value for Address 2 is FLOUTA, FLOUTB = OFF. During a flash event, both FLOUTA and FLOUTB will be enabled regardless of the movie-mode setting. Selection Data
1* 2 3 4 FLOUTA OFF OFF** ON ON FLOUTB OFF ON OFF** ON
Flash Timeout = 7.98s/F * 47nF = 375ms
The relationship between the flash safety timeout and the capacitance of the timer capacitor is illustrated in Figure 2.
1200
Flash Timeout (ms)
1000 800 600 400 200 0 0
Table 4: Address 2, Movie Mode Output Configuration.
20 40 60 80 100 120 140
CT Capacitor (nF)
Figure 2: Flash Safety Timeout vs. Timer Capacitor.
* Denotes the default value. ** A small current will flow due to the start-up test current.
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Flash to Maximum Movie Mode Current Ratio - Address 3
The maximum movie-mode current is a fixed ratio of the flash current controlled by Address 3. The ratio may be varied from 1:2 to OFF in 16 linear steps as shown in Table 5. The default value for Address 3 is Data=4 and represents a flash to maximum movie mode current level of 1 to 7.3. Data
1 2 3 4* 5 6 7 8 9 10 11 12 13 14 15 16
1.5A Step-Up Current Regulator for Flash LEDs
Shutdown
Since the sink switches are the only power returns for all loads, there is no leakage current to load if all the sink switches are disabled. When EN/SET pin is held low for an amount of time greater than tOFF (500s), the AAT1271 enters shutdown mode and draws less than 1A from VIN. All data and address registers are cleared (reset to 0) during shutdown.
FL to MM Ratio
1/2 1/3.8 1/5.5 1/7.3 1/8.9 1/10.5 1/12.2 1/13.8 1/14.9 1/16.5 1/18 1/19.6 1/21.1 1/22.6 1/24 OFF
Selecting the Boost Inductor
The AAT1271 controller utilizes PWM control and the switching frequency is fixed. To maintain 2MHz maximum switching frequency and stable operation, a 1H inductor is recommended. Manufacturer's specifications list both the inductor DC current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the saturation characteristics. Measurements at full load and high ambient temperature should be performed to ensure that the inductor does not saturate or exhibit excessive temperature rise. The inductor (L) is selected to avoid saturation at minimum input voltage and maximum output load conditions. Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Bench measurements are recommended to confirm actual IPEAK and to ensure that the inductor does not saturate at maximum LED current and minimum input supply voltage. The RMS current flowing through the boost inductor is equal to the DC plus AC ripple components. Under worst case RMS conditions, the current waveform is critically continuous. The resulting RMS calculation yields worst case inductor loss. The RMS current value should be compared against the inductor manufacturer's temperature rise, or thermal derating guidelines:
Table 5: Address 3, Flash/Movie Mode Current Ratio. The default maximum movie mode current can be calculated:
IMOVIE MODE[A/B] =
IFLOUT[A/B]MAX 7.3
For example, if an RSET value of 107k is chosen, then the FLOUTA/FLOUTB flash current is set to 750mA. For movie mode operation, the maximum current available at either FLOUTA or FLOUTB is then:
IRMS =
IPEAK 3
IMOVIE MODE[A/B] =
IFLOUT[A/B]MAX 750mA = = 103mA 7.3 7.3
The maximum movie mode current level can be calculated using the following equation:
81k x A 1 = = Max Movie Mode Current RSET FL to MM Ratio
For a given inductor type, smaller inductor size leads to an increase in DCR winding resistance and, in most cases, increased thermal impedance. Winding resistance degrades boost converter efficiency and increases the inductor's operating temperature:
IMOVIEMODE[A/B] =
PLOSS(INDUCTOR) = I2RMS * DCR
*Denotes the default value.
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1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
Selecting the Boost Capacitors
In general, it is good design practice to place a decoupling capacitor (input capacitor) between the IN and GND pins. An input capacitor in the range of 2.2F to 10F is recommended. A larger input capacitor in this application may be required for stability, transient response, and/or ripple performance. The high output ripple inherent in the boost converter necessitates the use of low impedance output filtering. Multi-layer ceramic (MLC) capacitors provide small size and adequate capacitance, low parasitic equivalent series resistance (ESR) and equivalent series inductance (ESL), and are well suited for use with the AAT1271 boost regulator. MLC capacitors of type X7R or X5R are recommended to ensure good capacitance stability over the full operating temperature range. The output capacitor is selected to maintain the output load without significant voltage droop (VOUT) during the power switch ON interval. A 2.2F ceramic output capacitor is recommended (see Table 7). Typically, 6.3V or 10V rated capacitors are required for this flash LED boost output. Ceramic capacitors selected as small as 0603 are available which meet these requirements. MLC capacitors exhibit significant capacitance reduction with applied voltage. Output ripple measurements should confirm that output voltage droop and operating stability are within acceptable limits. Voltage derating can minimize this factor, but results may vary with package size and among specific manufacturers. To maintain stable operation at full load, the output capacitor should be selected to maintain VOUT between 100mV and 200mV. The boost converter input current flows during both ON and OFF switching intervals. The input ripple current is less than Inductance (H)
1 1 1 1 1
1.5A Step-Up Current Regulator for Flash LEDs
the output ripple and, as a result, less input capacitance is required.
PCB Layout Guidelines
Boost converter performance can be adversely affected by poor layout. Possible impact includes high input and output voltage ripple, poor EMI performance, and reduced operating efficiency. Every attempt should be made to optimize the layout in order to minimize parasitic PCB effects (stray resistance, capacitance, and inductance) and EMI coupling from the high frequency SW node. A suggested PCB layout for the AAT1271 1.5A step-up regulator is shown in Figures 3 and 4. The following PCB layout guidelines should be considered: 1. Minimize the distance from capacitor CIN and COUT's negative terminals to the PGND pins. This is especially true with output capacitor COUT, which conducts high ripple current from the output to the PGND pins. Minimize the distance under the inductor between IN and switching pin SW; minimize the size of the PCB area connected to the SW pin. Maintain a ground plane and connect to the IC PGND pin(s) as well as the PGND connections of CIN and COUT. Consider additional PCB exposed area for the flash LEDs to maximize heatsinking capability. This may be necessary when using high current application and long flash duration application. Connect the exposed paddle (bottom of the die) to either PGND or GND. Connect AGND, FLGND to GND as close as possible to the package. DCR (m)
48 45 44.8 48.8 60
2.
3.
4.
5.
Manufacturer
Cooper Bussmann Cooper Bussmann Cooper Bussmann Sumida Coilcraft
Part Number
SD3812-1R0-R SDH3812-1R0-R SD10-1R0-R CDH38D11/S LPS4012-102NLC
Saturated Rated Current (A)
2.69 3 2.25 2.8 2.5
Size (mm) LxWxH
4.0x4.0x1.2 3.8x3.8x1.2 5.2x5.2x1.0 4.0x4.0x1.2 4.1x4.1x1.2
Type
Shielded Shielded Shielded Shielded Shielded Drum Drum Drum Drum Drum Core Core Core Core Core
Table 6: Typical Suggested Surface Mount Inductors. Manufacturer Part Number
GRM185R60J225KE26 GRM188R71A225KE15 GRM21BR70J225KA01 GRM21BR71A225KA01 GRM219R61A475KE19 GRM21BR71A106KE51
Capacitance (F)
2.2 2.2 2.2 2.2 4.7 10
Voltage Rating (V)
6.3 10 6.3 10 10 10
Temp Co.
X5R X7R X7R X7R X5R X7R
Case Size
0603 0603 0805 0805 0805 0805
Murata
Table 7: Typical Suggested Surface Mount Capacitors.
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
DC+ DC-
1.5A Step-Up Current Regulator for Flash LEDs
JP6 MCU R5 10K SW1 R6 10K R7 10K
1 2 3 4
JP7 0 U2 VDD GP5 GP4 GP3 VSS GP0 GP1 GP2
8 7 6 5
R10 10k
C4 1F
FLEN
R9 330 LED2 GRN R8 330 LED 1 RED
0
FLINH
SW4 JP3
0 2 4 1 3 5
Movie Mode Control Safety Timer
0 2 4
SW5 JP4 VOUT JP1 0 JP2 0
1 3 5
2 4
1 3 5
SW2
0 2 4 1 3 5
PIC12F675C3
R3 100k
SW3
R4 100k ( opt) U1
A/B Control
0 2 4
1 3 5
D1 RSET FLA FLGND FLB FLINH GND OUT
14 13 12 11 10 9 8
D2
JP5 EN /SET
R2 100K L1 C1 2.2F 1H C3 74 nF
1 2 3 4 5 6 7
CT EN/SET FLEN AGND IN SW PGND
AAT1271 TDFN33-14 R1 107k
C2 2.2F
L1 C1, C2 C3 D1, D2
Cooper Bussmann SD3812-1R0-R, 1H, 2.69A, 48m Murata GRM188R71A225KE15 2.2F, 0603, X7R, 10V Murata GRM155R71A743KA01, 74nF, 0402, X7R, 10V Lumiled LXCL-PWF4 or equivalent
Figure 2: AAT1271 Evaluation Board Schematic.
Figure 3: AAT1271 Evaluation Board Top Side Layout.
Figure 4: AAT1271 Evaluation Board Bottom Side Layout.
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1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
Component
U1 U2 SW1 - SW3 R1 R2, R3, R4 R5, R8 R6, R7 JP1, JP2, JP7 C1, C2 C3 C4 L1 D1-D2 LED1 LED2 JP3, JP4, JP5, JP6
1.5A Step-Up Current Regulator for Flash LEDs
Part Number
AAT1271IWO PIC12F675 PTS645TL50 Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor GRM188R71A225KE15 GRM155R71A743KA01 GRM216R61A105KA01 SD3812-1R0-R LXCL-PWF4 CMD15-21SRC/TR8 CMD15-21VGC/TR8 PRPN401PAEN
Description
1.5A Step-Up Current Regulator for Flash LEDs; TDFN33-14 package 8-bit CMOS, FLASH-based C; 8-pin PDIP package Switch, SPST, 5mm 107k, 1%, 1/4W; 0402 100k, 1%, 1/4W; 0603 10k, 5%, 1/4W; 0603 330, 5%, 1/4W; 0603 0, 5% 2.2F, 10V, X7R, 0603 74nF, 10V, X7R, 0402 1F, 10V, X5R, 0805 Drum Core, 1H, 2.69A, 48m White Flash LED Red LED; 1206 Green LED; 1206 Conn. Header, 2mm zip
Manufacturer
AnalogicTech Microchip ITT Industries Vishay Vishay Vishay Vishay Vishay Murata Murata Murata Cooper Bussmann Lumileds, Philips Chicago Miniature Lamp Chicago Miniature Lamp Sullins Electronics
Table 8: AAT1271 Evaluation Board Bill of Materials.
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PRODUCT DATASHEET
AAT1271
SwitchRegTM
Ordering Information
Package
TDFN33-14
1.5A Step-Up Current Regulator for Flash LEDs
Marking1
ZUXYY
Part Number (Tape and Reel)2
AAT1271IWO-T1
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/about/quality.aspx.
Package Information
TDFN33-143
Detail "A" Index Area
3.000 0.050
3.000 0.050
1.650 0.050
Top View
Bottom View
0.425 0.050
0.750 0.050
0.000
Side View
Pin 1 Indicator (Optional)
Detail "A"
All dimensions in millimeters.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN, and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
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0.180 0.050
0.400 BSC
+ 0.100 - 0.000
0.203 REF
2.500 0.050
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM 1.5A Step-Up Current Regulator for Flash LEDs
Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611
(c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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