AIC1578
High-Efficiency, Step-Down DC/DC Converter
Analog Integrations Corporation 4F, 9, Industry E. 9th Rd, Science Based Industrial Park, Hsinchu Taiwan, ROC www.analog.com.tw
DS-1578-02 Dec 27, 00 TEL: 886-3-5772500 FAX: 886-3-5772510 1
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.
APPLICATIONS
•Notebook 5V/3.3V Main Power
•Step-Down DC/DC Converter Module.
• Constant Current Source for Battery Chargers.
TYPICAL APPLICATION CIRCUIT
CS+
CS -
DRI
DUTY
FB GND
SHDN
VIN
C4
C3
Battery
D2
**Charge current=57mV/RS
+
1N5820
220µF
33µH
* L1
AIC1578
**RS
+
10µF
Q1
C2
0.1µF
D1
1N5820
RDUTY
1M
R2
1M
C1
Control
*Sumida MPP CORE
VIN
+
IRF9Z34
100
µ
F
Constant Current Source for Battery Charger
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 Pulse-
Skipping 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.
ORDERING INFORMATION
AIC1578 XX ORDER NUMBER
AIC1578CN
(PLASTIC DIP)
PIN CONFIGURATION
AIC1578CS
(PLASTIC SO)
TOP VIEW
DRI
CS+
DUTY
FB
CS-
GND
VIN
SHDN
PACKAGE TYPE
N: PLASTIC DIP
S: SMALL OUTLINE
TEMPERATURE RANGE
C: 0°C~+70°C
1
3
4
2
8
6
5
7
AIC1578
2
ABSOLUTE MAXIMUM RATINGS
VIN Supply Voltage .....…………............................................................................. 20V
DUTY Voltage .........................................……………................................................ 20V
SHDN Voltage ......................................………….................................................... 15V
Operating Temperature Range ................…………......................................... 0°C~70°C
Storage Temperature Range ......................…………................................. -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 4 20 V
Quiescent Current VFB = 1.5V 90 160 µA
Shutdown Mode Current VSHDN = 0V 8 20 µA
Internal Reference Voltage 1.16 1.22 1.28 V
Driver Sinking "ON Resistance" 16 Ω
Driver Sourcing "ON Resistance" 11 Ω
Current Limit Sense Threshold VCS+ = 13V 50 70 90 mV
Shutdown Threshold 0.8 1.5 2.4 V
SHDN Pin Leakage Current VSHDN < 15V 1 µA
Duty Cycle VDUTY = VIN 71 %
Oscillator Frequency VDUTY = VIN 225 KHz
AIC1578
3
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency & Duty Cycle vs VIN
VIN ( V)
Duty (%)
55
60
65
70
75
80
85
90
Duty
4 6 8 101214161820
Ta = 27°C
Frequency
Frequency (KHz)
0
50
10
15
20
25
30
35
Temperature (°C)
Duty Cycle vsTemperature
Duty Cycle (%)
VIN=5V
0 20406080
60
65
70
75
80
85
90
VIN=20V
VIN=13V
Temperature (°C)
Frequency vs Temperature
Frequency (KHz)
0 10203040506070
90
140
190
240
290
VIN=5V
VIN=13V
VIN=20V
RDUTY
(
MΩ
)
Duty Cycle vs RDUTY
Duty Cycle (%)
01234
60
70
80
90
10
VIN=20V
VIN=10V
VIN=15V
VIN=5V
RDUTY refer to Typ. App.
VIN (V)
Shutdown Current vs VIN
Shutdown Current (µA)
2046 81012141618
0
5
10
15
20
Ta=0°C
Ta=25°C
Ta=70°C
VIN (V)
Quiescent Current vs VIN
Quiescent Current (
µ
A)
468101214161820
60
70
80
90
100
11
Ta= 25°C
Ta= 70°C
Ta= 0°C
AIC1578
4
BLOCK DIAGRAM
70mV 8
7
6
5
4
3
2
1
Current Limit Comparator
Output
Dr iv er GND
DRI
CS+
CS-
VI
N
PFM
OSC
1.22V
Ref er enc e
Volta
g
e
Error
Comparator
DUTY
FB
SHDN
VIN
+
-
LATCH
-
+
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:
VSHDN = High for normal
operation.
VSHDN = 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.
PIN 7: CS- - Current sense comparator
inverting input, not to exceed VIN
voltage.
PIN 8: CS+ - Current sense comparator non-
inverting input, not to exceed VIN
voltage.
AIC1578
5
APPLICATION EXAMPLES
AIC1578
CS+
CS-
DRI
DUTY
FB GND
SHDN
VIN
*:Sumida MPP Core
5V
VOUT
VIN
6.4 ~ 20V
33µH
5V/2A
100µF
+
15.4K
R2
47K
R1
0.1µF
300µF
C3
1N5820
D1
IRF9Z34
+
*L1
Q1
C1
C2
Load Current (mA)
Efficiency vs Load Current
Efficiency (%)
100
10 100 1000
80
85
90
95
VIN=6.4
V
VIN=9V
VIN=16
V
VOUT=5V
Fig. 1 5V Step-Down Converter
AIC1578
CS+
CS-
DRI
DUTY
FB GND
SHDN
VIN
*:Sumida MPP Core
5V
VOUT
VIN
6 ~ 20V
33µH
3.3V/2A
100µF
+
27.4K
R2
47K
R1
0.1µF
300µF
C3
1N5820
D1
IRF9Z34
+
*L1
Q1
C1
C2
Load Current (mA)
Efficiency vs Load Current
95
10 10 1000
75
80
85
90 VIN=6V
VIN=9V
VIN=16V
VOUT=3.3V
Efficiency (%)
Fig. 2 3.3V Step-Down Converter
AIC1578
6
Q1
D3
1N4148
C6
0.1µF
C8
C2
0.1µF
R7
0.1µF
R6
150K
390K
R11
1.5K
R10
1.5K
D2
D1
1N5820
1N5820
*L1
R8
33µH
R13
1M
RS
150K
R5
1M 1M
R4 220
C3
C1
C4
C5
*:Sumida MPP Core
IRF9Z34
100µF
VB
A
TT
+
Fast Charge
4.7µF
10µF
220µF
BATTERY
1K
++
+
C7
100µF
+
GND
LEDMODE
TIMER
VBT
VDD
VOUT
VREF
CS+
CS-
DRI
DUTY
FB GND
SHDN
VIN
VIN
RDUTY
1M
R9
Trickle Charge
AIC1761/1766
AIC1578
R12
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)
SYMBOL MIN MAX
A 1.35 1.75
A1 0.10 0.25
B 0.33 0.51
C 0.19 0.25
D 4.80 5.00
E 3.80 4.00
e 1.27(TYP)
H 5.80 6.20
L 0.40 1.27
D
H
e
A
B
A1
C
E
L
AIC1578
7
8 LEAD PLASTIC DIP (unit: mm)
SYMBOL MIN MAX
A1 0.381 —
A2 2.92 4.96
b 0.35 0.56
C 0.20 0.36
D 9.01 10.16
E 7.62 8.26
E1 6.09 7.12
e 2.54 (TYP)
eB — 10.92
be
L
A2
A1
eB
E
C
E1
D
L 2.92 3.81
