AIC1578
High-Efficiency, Step-Down DC/DC Converter
FEATURES
• 4V to 20V Input Voltage Operation. • High Efficiency (up to 95%). • Low Quiescent Current at 90µA. • Pulse-Skipping and Pulse-Frequency Modulation. • Inputs-Uncommitted Current Sense Comparator. • Duty Cycle Adjustable. • 90KHz to 280KHz Oscillator Frequency. • Power-Saving Shutdown Mode (8µA Typical). • Push-Pull Driver Output.
DESCRIPTION
The AIC1578 is a high performance step-down DC/DC converter, designed to drive an external P-channel MOSFET to generate programmable output voltages. Two main schemes of PulseSkipping and Pulse-Frequency 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 90µA and can be reduced to 8µA in shutdown mode. Switching frequency being in around 90KHz to 280KHz range, small size switching components are ideal for battery powered portable equipment.
APPLICATIONS
• Notebook 5V/3.3V Main Power • Step-Down DC/DC Converter Module. • Constant Current Source for Battery Chargers.
TYPICAL APPLICATION CIRCUIT
VIN IRF9Z34 Q1 * L1 33µH D1 1N5820 C3 220µF + C4 10µF **RS +
D2 100µF + 0.1µF C2 RDUTY R2 1M 1M Control *Sumida MPP CORE VIN DUTY SHDN FB AIC1578 **Charge current=57mV/RS CS+ CS DRI GND Battery
C1
Constant Current Source for Battery Charger
ORDERING INFORMATION
AIC1578 XX PACKAGE TYPE N: PLASTIC DIP S: SMALL OUTLINE TEMPERATURE RANGE C: 0 ° C~+70 ° C
1N5820
ORDER NUMBER AIC1578CN (PLASTIC DIP)
PIN CONFIGURATION
TOP VIEW VIN DUTY 1 2 3 4 8 CS+ 7 CS6 DRI 5 GND
AIC1578CS (PLASTIC SO)
SHDN FB
Analog Integrations Corporation DS-1578-02 Dec 27, 00
4F, 9, Industry E. 9th Rd, Science Based Industrial Park, Hsinchu Taiwan, ROC TEL: 886-3-5772500 FAX: 886-3-5772510
www.analog.com.tw
1
AIC1578
ABSOLUTE MAXIMUM RATINGS
VIN Supply Voltage DUTY Voltage .....…………............................................................................. 20V .........................................……………................................................ 20V ......................................………….................................................... 15V
SHDN Voltage
Operating Temperature Range Storage Temperature Range
................…………......................................... 0°C~70°C
......................…………................................. -65°C~ 150°C
TEST CIRCUIT
Refer to Fig. 1 circuit of Application Examples.
ELECTRICAL CHARACTERISTICS (VIN= 13V, Ta=25°C, unless otherwise
specified.)
PARAMETERS CONDITIONS MIN. TYP. MAX. UNIT
Operation Voltage Quiescent Current Shutdown Mode Current Internal Reference Voltage Driver Sinking "ON Resistance" Driver Sourcing "ON Resistance" Current Limit Sense Threshold Shutdown Threshold SHDN Pin Leakage Current Duty Cycle Oscillator Frequency V SHDN < 15V VDUTY = VIN VDUTY = VIN VCS+ = 13V VFB = 1.5V V SHDN = 0V
4 90 8 1.16 1.22 16 11 50 0.8 70 1.5
20 160 20 1.28
V
µA µA
V
Ω Ω
90 2.4 1
mV V
µA
71 225
% KHz
2
AIC1578
TYPICAL PERFORMANCE CHARACTERISTICS
90 85 80
Frequency & Duty Cycle vs VIN Ta = 27°C Duty Frequency
35 30 25 20 15 10 50 0 20
90 85
Duty Cycle vsTemperature
Frequency (KHz)
VIN=5V Duty Cycle (%)
80 75 70 65 60 0 20
Duty (%)
75 70 65 60 55 4
VIN=13V
VIN=20V
6
8
10
12
14
16
18
VIN ( V)
Temperature (°C)
40
60
80
Frequency vs Temperature
10
290
Duty Cycle vs RDUTY VIN=5V
VIN=20V
Frequency (KHz)
90
240
Duty Cycle (%)
190
VIN=13V
80
VIN=10V VIN=15V
140
VIN=5V
70
VIN=20V RDUTY refer to Typ. App.
90 0
10
20
30
40
50
60
70
Temperature (°C)
60 0
1
RDUTY (MΩ)
2
3
4
20
Shutdown Current vs VIN
11
Quiescent Current vs VIN
Shutdown Current (µA)
Ta=25°C Ta=0°C
Quiescent Current (µA)
15
100
Ta= 0°C
90
10
80
Ta= 25°C Ta= 70°C
5
Ta=70°C
70
0
4
6
8
10
12
14
16
18
20
60 4
6
8
10
VIN (V)
VIN (V)
12
14
16
18
20
3
AIC1578
BLOCK DIAGRAM
Current Limit Comparator VIN 1 + 70mV 8 CS+
DUTY 2 PFM OSC LATCH
VIN
7
CS-
SHDN
3
+ Error Comparator 1.22V Reference Voltage Output Driver
6
DRI
FB
4
5
GND
PIN DESCRIPTIONS
PIN 1: VIN - 4V to 20V input supply voltage. PIN 2: DUTY - Duty cycle adjustment pin. To be tied to the VIN pin directly or through a resistor RDUTY to adjust oscillator duty cycle. RDUTY must be above 1MΩ if VIN=20V. See TYPICAL PERFORMANCE CHARACTERISTICS. PIN 3: SHDN- Logical input to shutdown the chip: V SHDN = High for normal operation. V SHDN = Low for shutdown. This pin should not be floating or forced to greater than 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 voltage. Connecting a resistor R1 to converter output node and a resistor R2 to ground yields the output voltage: VOUT=1.22 ×(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, not to exceed VIN voltage.
PIN 7: CS-
PIN 8: CS+ - Current sense comparator noninverting input, not to exceed VIN voltage.
4
AIC1578
APPLICATION EXAMPLES
Efficiency vs Load Current
100
VOUT=5V
C2 100µF 0.1µ F VIN + C1 6.4 ~ 20V
95
VIN
CS+ IRF9Z34 Q1
Efficiency (%)
5V
DUTY CSAIC1578 DRI SHDN FB GND
90
VIN=6.4 V
VIN=9V
33µH *L1 +
VOUT 5V/2A
1N5820 D1 R2 15.4K R1 47K
300µF C3
85
VIN=16 V
100 1000
80 10
*:Sumida MPP Core
Load Current (mA)
Fig. 1 5V Step-Down Converter
Efficiency vs Load Current VOUT=3.3V
0.1µF C2 100µF + C1 VIN 6 ~ 20V
90
95
VIN=6V
VIN
5V
CSDUTY AIC1578 DRI SHDN FB GND
IRF9Z34 Q1
Efficiency (%)
CS+
85
33µH *L1 300µF C3 +
VOUT 3.3V/2A
VIN=9V
80
1N5820 D1 R2 27.4K R1 47K
VIN=16V
75 10 10 1000
*:Sumida MPP Core
Load Current (mA)
Fig. 2 3.3V Step-Down Converter
5
AIC1578
R4 IRF9Z34 VIN Q1 1K D1 1N5820 33µH *L1 C3 1N4148 D3 + 220µF RS 1N5820 D2 BATTERY VBATT R6 390K R8 4.7µF + 150K C6 C5 R7 150K 1M R12 0.1µF Trickle Charge 220 R9 C7 100µF + R10 1.5K C8 0.1µF
Fast Charge
C4 + 10µF
R11 1.5K
C1
+
0.1µF
C2 R13 1M
RDUTY VIN DUTY 1M 1M SHDN R5 FB
100µF
CS+ CSDRI GND
VBT GND TIMER MODE
VREF VDD VOUT LED
AIC1578
AIC1761/1766
*:Sumida MPP Core
NOTE:
RS =0.1Ω, charge current =0.5A ±10%, VIN>VBATT +3.5V RS =0.05Ω, charge current =1A±10%, VIN>VBATT +4V RS =0.033Ω, charge current =1.5A ±10%, VIN>VBATT +4.5V Efficiency>90%, measured at CS- node
Fig. 3 Battery Charge Circuit with High-Side Current Sensing Constant Current Source
PHYSICAL DIMENSIONS
8 LEAD PLASTIC SO (unit: mm)
D
SYMBOL A
H E
MIN 1.35 0.10 0.33 0.19 4.80 3.80
MAX 1.75 0.25 0.51 0.25 5.00 4.00
A1 B C
e A C
A1
D E e H
L
1.27(TYP) 5.80 0.40 6.20 1.27
B
L
6
AIC1578
8 LEAD PLASTIC DIP (unit: mm)
D
SYMBOL A1
E1
MIN 0.381 2.92 0.35 0.20 9.01 7.62 6.09
MAX — 4.96 0.56 0.36 10.16 8.26 7.12
A2 b
E
C D E
C
A2 A1
L
E1 e eB L
eB b e
2.54 (TYP) — 2.92 10.92 3.81
7
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