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AIC1578
High-Efficiency, Step-Down DC/DC Controller
n FEATURES
l l l l l l l l
n DESCRIPTION
The AIC1578 is a high performance step-down DC/DC controller, designed to drive an external P-channel MOSFET to generate programmable output voltages. Two and main schemes of Pulse-Skipping Pulse-Frequency
High Efficiency (up to 95%). Low Quiescent Current at 90A. Pulse-Skipping and Pulse-Frequency Modulation. Inputs-Uncommitted Current Sense Comparator. Duty Cycle Adjustable. 90KHz to 280KHz Oscillator Frequency. Power-Saving Shutdown Mode (8A Typical). Push-Pull Driver Output.
Modulation are employed to maintain low quiescent current and high conversion efficiency under wide ranges of input voltage and loading condition. The AIC1578 delivers 10mA to 2A of output current with 87%~93% efficiency at VIN=9V, VOUT=5V condition. A current sense comparator with both inverting and non-inverting input uncommitted is included to provide the crucial function of either current limit protection or constant output current control. When the AIC1578 is used in a high-side current sensing step-down constant current source, the efficiency is typically greater than 90%. Duty cycle can be adjusted to greater than 90% by connecting a resistor from DUTY pin to VIN. Quiescent current is about 90A and can be reduced to 8A in shutdown mode. Switching frequency being in around 90KHz to 280KHz range, small size switching components are ideal for battery powered portable equipment.
n APPLICATIONS
l l l l
LCD Monitors Notebook Computers Step-Down DC/DC Controller Module. Constant Current Source for Battery Chargers.
Analog Integrations Corporation
4F, 9 Industry E. 9th Rd, Science-Based Industrial Park, Hsinchu, Taiwan TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw
DS-1578P-01 091503
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AIC1578
n TYPICAL APPLICATION CIRCUIT
VIN 6.4~18V VOUT 5V R1 12k R2 3.9K
* RS Q1 CEM4435
D1 SS32
L1 33H
+
C1 100F C2 0.1F
1 VIN RDUTY 2 DUTY 3 1M SHDN <15V 4 FB
CS+ CSDRI GND
8 7 6 5
C3 200F **R7
+
AIC1578
* RS should not be omitted so that inrush current won' be too high. t VO( VIN - VO) IP = IO,MAX + 2VIN x f S x L
RS =
0.1VIN f S L VTH 50mV = = IP IP 2VIN f S LIO,MAX + VIN VO - VO 2
VIN: Input voltage VOUT: Output voltage fS: Working frequency L= Inductor value IO,MAX: Maximum Output current VTH: Current Limit Sense Threshold **VIN>15V, R7=15 VIN15V, R7=0 DC/DC Buck Converter
n ORDERING INFORMATION
AIC1578XXXX PACKING TYPE TR: TAPE & REEL TB: TUBE PACKAGING TYPE S: SMALL OUTLINE N: PLASTIC DIP C: Commercial P: Lead Free Commercial (Available for PS only) PIN CONFIGURATION
SO-8 TOP VIEW VIN DUTY SHDN FB 1 2 3 4 8 CS+ 7 CS6 DRI 5 GND
Example: AIC1578CSTR a in SO-8 Package & Taping & Reel Packing Type (CN is not available in TR packing) AIC1578PSTR a in SO-8 Lead Free Package & Taping & Reel Packing Type
2
AIC1578
n ABSOLUTE MAXIMUM RATINGS
VIN Supply Voltage DUTY Voltage 20V 20V 15V -65C~ 150C
SHDN Voltage
Storage Temperature Range Recommended Operating Conditions VIN Supply Voltage Ambient Temperature Range Junction Temperature Range
18V1% 0C~ 70C 0C~ 100C
n TEST CIRCUIT
Refer to TYPICAL APPLICATION CIRCUIT.
n ELECTRICAL CHARACTERISTICS (V
specified.)
PARAMETERS Operation Voltage Quiescent Current Shutdown Mode Current Internal Reference Voltage Driver Sinking "ON Resistance" Driver Sourcing "ON Resistance" Current Limit Sense Threshold Shutdown Threshold VCS+ = 13V VFB = 1.5V V SHDN = 0V CONDITIONS
IN=
13V, TA=25C, unless otherwise
MIN. 4
TYP.
MAX. 20
UNIT V A A V
90 8 1.195 1.22 16 11 50 0.6 70 0.9
160 20 1.245
90 1.2 1
mV V A % KHz
SHDN Pin Leakage Current
Duty Cycle Oscillator Frequency
V SHDN < 15V VDUTY = VIN VDUTY = VIN 70 75 225
80
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AIC1578
n TYPICAL PERFORMANCE CHARACTERISTICS
95
95
VDUTY = VIN
90
260 240 90
Duty
85
Frequency (KHz)
Frequency
220 200
VIN=5V
85
Duty (%)
Duty (%)
80 75 70 65 60 4
180 160 140 120 100 80 6 8 10 12 14 16 18 20
80 75
VIN=13V
70
65
VIN=18V
-20 0
60 -40
20
40
60
80
100
Fig. 1
VIN (V) Frequency & Duty Cycle vs. VIN
Fig. 2
Temperature (C) Duty Cycle vs. Temperature
400 350 300
100
VIN =5V
90
250
VIN=13V
200 150 100 50
0
Duty Cycle (%)
Frequcny (%)
VIN=18V
80
VIN =15V VIN =10V
VIN=5V
70
VIN =20V
60 0 1 2 3 4
-40
-20
0
20
40
60
80
100
Fig. 3
Temperature (C) Frequency vs. Temperature
Fig. 4
RDUTY (M) Duty Cycle vs. RDUTY
20
125 120 115
Quiescent Current (A)
Shutdown Current (A)
15
110 105 100 95 90 85 80 75
TA=0C
TA=25C
10
TA=25C TA=70C
TA=0C TA=70C
5
0 4 6 8 10
12
14
16
18
20
70 4 6 8 10 12 14 16 18 20
Fig. 5
VIN (V) Shutdown vs. VIN
Fig. 6
VIN (V) Quiescent Current vs. VIN
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AIC1578
n BLOCK DIAGRAM
VIN 1 Current Limit Comparator + DUTY 2 PFM OSC VIN + Error Comparator 1.22V Reference Voltage Power Ready Output Driver 5 Buffer 6 DRI 7 CS70mV 8 CS+
3 SHDN
FB
4
GND
n PIN DESCRIPTIONS
PIN 1: VIN - Input supply voltage, ranged from 4V to 18V is recommended. PIN 2: DUTY - Duty cycle adjustment pin. To be tied to the VIN pin directly or through a resistor R DUTY to adjust oscillator duty cycle. RDUTY must be over 1M if VIN=20V. See TYPICAL PERFORMANCE CHARACTERISTICS. PIN 3: SHDN- Logical input to shutdown the chip: VSHDN = High for normal operation. = Low for shutdown. V
SHDN
voltage. Connecting a resistor R1 to converter output node and a resistor R2 to ground yields the output voltage: VOUT=1.22 x (R1+R2)/ R2 PIN 5: GND - Power ground. PIN 6: DRI - Push-pull driver output to drive an external P-channel MOSFET or PNP transistor. When driving a PNP bipolar transistor, a base resistor and a capacitor to the base of PNP are recommended. - Current sense comparator inverting input. This pin voltage should go over 2V but not to exceed VIN voltage.
PIN 7: CS-
This pin should not be floating or be forced to over 15V. In shutdown mode DRI pins is at high level. PIN 4: FB - Feedback comparator input, to compare the feedback voltage with the internal reference
PIN 8: CS+ - Current sense comparator non-inverting input. This pin voltage should go over 2V but not to exceed VIN voltage.
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AIC1578
n APPLICATION EXAMPLES
Efficiency vs. Load Current
C2 100F 0.1F VIN + C1 6.4 ~ 18V
100
VOUT=5V
95
VIN DUTY 5V SHDN FB AIC1578 R2 15.4K VIN>15V, R7=15 VIN15V, R7=0
CS+ RS CSDRI GND GS SS32 D1 R1 47K *:Sumida MPP Core
80 10
100 1000
*R7
VOUT 5V/2A +
Efficiency (%)
CEM4435 Q1 33H *L1 330F C3
VIN=6.4V
90
VIN=9V
85
VIN=16V
Load Current (mA)
Fig. 7 5V Step-Down Converter
VIN C1 12 ~ 18V
95
100F
0.1F
C2
+
Efficiency vs. Load Current VOUT=3.3V
VIN DUTY 5V SHDN FB
CS+ CSDRI GND AIC1578
RS R7 CEM4435 Q1 33H *L1 GS SS32 D1 R1 47K *:Sumida MPP Core 330F C3 + VOUT
90
Efficiency (%)
3.3V/2A
85
R2 27.4K VIN>15V, R7=15 VIN15V, R7=0
80
VIN=16V
75 10 10 1000
Load 0 Current (mA)
Fig. 8 3.3V Step-Down Converter
6
AIC1578
n APPLICATION EXAMPLES (Continued)
VIN 5~8V R4 1K 1N4148 33H *L1 D1 SS32 U1 VIN + C1 100F C2 0.1F R6 RDUTY DUTY R1 1M FB R7 ** AIC1578 1M SHDN DRI GND CSC3 *RS + C4 10F D2 CEM4435 Q1 D3 + 330F 35V
SS32
CS+
VBATT R3 R2 20/5W LED1 R8 240K + R9 100K C9 4.7F C7 0.1F R10 100K YELLOW 1 PEAK 2 C10 47nF Q3
9014
SW1 LED2 PB SW R12 100K DSW ICON LED2 LED1 GND SEL1 SEL2 MODE 16 15 14 13 12 11 10 9 R16 680 R17 680 GREEN RED LED3
510
U2
R15 680
VBT 3 DIS 4 VTS 5 VCC
BAT1 RX BATTERY
THERMISTOR
6 R14 + C11 200K C8 7 8 R11 240K
ADJ SEL3 TMR
100K RY 100K C6 0.1F
100F R13 470K
0.1F
AIC1781
Q2 MMBT2222A
U3
+
78L05 VOUT GND
+ C13
*:Sumida MPP Core VIN>15V, R7=15 VIN15V, R7=0
VIN C12 1F
10F
NOTE:
RS =0.1, charge current =0.5A 10%, VIN>VBATT +3.5V RS =0.05, charge current =1A10%, VIN>VBATT +4V RS =0.033, charge current =1.5A 10%, VIN>VBATT +4.5V Efficiency>90%, measured at CS- node 3~5 NiMH/NiCd Cells
Fig. 9 Battery Charge Circuit with High-Side Current Sensing Constant Current Source
7
AIC1578
n APPLICATION INFORMATION
Short Circuit Protection Design 1. As we know, Short Circuit Protection Fuse select guide: Fuses, which can take the start up current, and break down fast on unexpected current. Note: Replacement of fuse is needed after short circuit. 3. Design 2: shown as Fig. 11. Method: Add a SCP circuit Note: 1. The time constant, which is directly related to R1 and C1, has a serious effect on the circuit. 2. Circuit can be recovered by removing the short circuit event from the system. 3. The condition for applying this design is VOUT 3V. (abbreviated as SCP) does not always exist in the DC-DC converter circuit. The fact is usually the DC-DC converter provides the circuits attached to VOUT with low power or low voltage. Sometimes it has less concern about safety. And its probability of short-circuit is quite low. That gives users reasons to ignore the use of SCP circuit. However, we would still like to point out the importance of the protection. With SCP, the system will be well protected in any situation. Two SCP circuits are introduced as follows for your reference. 2. Design1: shown as Fig. 10. Method: Add a fast fuse to VOUT.
+VIN 12V
Rs 20mR Q2 CEM4435 L2 D2 SS32 33H
FUSE1 +VOUT, 5V/2A Fast 3A
1 VIN + C5 470/16V 2 DUTY C2 0.1F 3 SHDN 4 FB U2
CS+ CSDRI GND AIC1578
8 7 C4 +
R8 12K R9 3K9
6 1500F/6.3V 5
Fig 10. Add a Fast Fuse Solution
8
AIC1578
+VIN 12V R1 240K C1 1F Rs R2 10K Q1 PNP mmbt3906 20mR Q2 CEM4435 L2 33H D2 SS32 C4 1 2 + 470F C5 16V C2 0.1F 3 4 8 7 6 5 1500F 6.3V + +VOUT, 5V/2A
VIN DUTY SHDN FB
CS+ CSDRI GND
R8 12K R9 3K9
U2 AIC1578
LL4148
D1
5.1K
Short Circuit Protection
Fig 11. Add A Short Circuit Protection Circuit Solution
n PHYSICAL DIMENSIONS (unit: mm)
l 8 LEAD PLASTIC SO (CS) (PS)
D
SYMBOL A
H E
MIN 1.35 0.10 0.33 0.19 4.80 3.80 5.80 0.40
MAX 1.75 0.25 0.51 0.25 5.00 4.00 6.20 1.27
A1 B C D E
e A C A1
e H L
L
1.27(TYP)
B
9
AIC1578
l
8 LEAD PLASTIC DIP (CN)
D
SYMBOL A1
E1
MIN 0.381 2.92 0.35 0.20 9.01 7.62 6.09 -- 2.92
MAX -- 4.96 0.56 0.36 10.16 8.26 7.12 10.92 3.81
A2 b C
E
D
A2 A1
L
E
C eB
E1 e eB L
2.54 (TYP)
b
e
Note:
Information provided by AIC is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AIC product; nor for any infringement of patents or other rights of third parties that may result from its use. We reserve the right to change the circuitry and specifications without notice. Life Support Policy: AIC does not authorize any AIC product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (ii) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
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