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 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.
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
B
a
tte
ry
D2
**Charge current=57mV/RS
+
1N
58
20
220
F
33
H
* L1
AIC1578
**RS
+
10
F
Q1
C2
0.
1
F
D1
1N5820
R
DUTY
1M
R2
1M
C1
Control
*Sumida MPP CORE
V
IN
+
IRF9Z34
100
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 V
IN
=9V, V
OUT
=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
V
IN
. Quiescent current is about 90
A and can be
reduced to 8
A 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~+70C
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~70C
Storage Temperature Range
...................................................................
-65
C~ 150C
TEST CIRCUIT
Refer to Fig. 1 circuit of Application Examples.
ELECTRICAL CHARACTERISTICS
(V
IN
= 13V, Ta=25
C, unless otherwise
specified.)
PARAMETERS
CONDITIONS
MIN.
TYP.
MAX.
UNIT
Operation Voltage
4
20
V
Quiescent Current
V
FB
= 1.5V
90
160
A
Shutdown Mode Current
V
SHDN
= 0V
8
20
A
Internal Reference Voltage
1.16
1.22
1.28
V
Driver Sinking "ON Resistance"
16
Driver Sourcing "ON Resistance"
11
Current Limit Sense Threshold
V
CS+
= 13V
50
70
90
mV
Shutdown Threshold
0.8
1.5
2.4
V
SHDN Pin Leakage Current
V
SHDN
< 15V
1
A
Duty Cycle
V
DUTY
= V
IN
71
%
Oscillator Frequency
V
DUTY
= V
IN
225
KHz
AIC1578
3
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency & Duty Cycle vs V
IN
V
IN
( V)
Duty
(
%
)
55
60
65
70
75
80
85
90
Duty
4
6
8
10
12
14
16
18
20
Ta =
27
C
Frequency
Fr
equen
cy
(
K
Hz
)
0
50
10
15
20
25
30
35
Temperature (
C)
Duty Cycle vsTemperature
Dut
y
Cy
c
l
e
(
%
)
V
IN
=5V
0
20
40
60
80
60
65
70
75
80
85
90
V
IN
=20V
V
IN
=13V
Temperature (
C)
Frequency vs Temperature
Fr
equency
(
K
Hz)
0
10
20
30
40
50
60
70
90
140
190
240
290
V
IN
=5V
V
IN
=13V
V
IN
=20V
R
DUTY
(M
)
Duty Cycle vs R
DUTY
Dut
y
Cy
c
l
e (
%
)
0
1
2
3
4
60
70
80
90
10
V
IN
=20V
V
IN
=10V
V
IN
=15V
V
IN
=5V
R
DUTY
refer to Typ. App.
V
IN
(V)
Shutdown Current vs V
IN
Sh
utd
o
wn
Cu
r
r
ent
(
A)
20
4
6
8
10
12
14
16
18
0
5
10
15
20
Ta=0
C
Ta=25
C
Ta=70
C
V
IN
(V)
Quiescent Current vs V
IN
Qu
ies
c
ent
Cur
r
ent
(
A)
4
6
8
10
12
14
16
18
20
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
Driver
GND
DRI
CS+
CS-
VIN
PFM
OSC
1.22V
Reference
Voltage
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 R
DUTY
to adjust
oscillator duty cycle. R
DUTY
must
be above 1M
if V
IN
=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:
V
OUT
=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 V
IN
voltage.
PIN 8: CS+ - Current sense comparator non-
inverting input, not to exceed V
IN
voltage.
AIC1578
5
APPLICATION EXAMPLES
AIC1578
CS+
CS-
DRI
DUTY
FB
GND
SHDN
VIN
*:Sumida MPP Core
5V
V
OUT
V
IN
6.4 ~ 20V
33H
5V
/
2
A
10
0
F
+
15.4K
R2
47K
R1
0.
1
F
300F
C3
1N5820
D1
IRF9Z34
+
*L1
Q1
C1
C2
Load Current (mA)
Efficiency vs Load Current
E
f
f
i
c
i
ency (
%
)
100
10
100
1000
80
85
90
95
V
IN
=6.4
V
V
IN
=9V
V
IN
=16
V
V
OUT
=5V
Fig. 1 5V Step-Down Converter
AIC1578
CS+
CS-
DRI
DUTY
FB
GND
SHDN
VIN
*:Sumida MPP Core
5V
V
OUT
V
IN
6 ~ 20V
33H
3.
3
V
/2
A
10
0
F
+
27.4K
R2
47K
R1
0.
1
F
300F
C3
1N5820
D1
IRF9Z34
+
*L1
Q1
C1
C2
Load Current (mA)
Efficiency vs Load Current
95
10
10
1000
75
80
85
90
V
IN
=6V
V
IN
=9V
V
IN
=16V
V
OUT
=3.3
V
E
f
fi
cie
n
cy (%
)
Fig. 2 3.3V Step-Down Converter
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