AIC1578
High-Efficiency, Step-Down DC/DC Controller
Analog Integrations Corporation 4F, 9 Industry E. 9th Rd, Science-Based Industrial Park, Hsinchu, Taiwan
DS-1578-04 032102
TEL: 886-3-5772500
FAX: 886-3-5772510
www.analog.com.tw
1
n
FEATURES
4V to 18V Input Voltage Operation.
High Efficiency (up to 95%).
Low Quiescent Current at 90
A.
Pulse-Skipping and Pulse-Frequency Modulation.
Inputs-Uncommitted Current Sense Comparator.
Duty Cycle Adjustable.
90KHz to 280KHz Oscillator Frequency.
Power-Saving Shutdown Mode (8
A Typical).
Push-Pull Driver Output.
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APPLICATIONS
Notebook 5V/3.3V Main Power
Step-Down DC/DC Controller Module.
Constant Current Source for Battery Chargers.
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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 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.
AIC1578
2
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TYPICAL APPLICATION CIRCUIT
VIN
1
DUTY
2
SHDN
3
FB
4
GND
5
DRI
6
CS-
7
CS
+
8
U1
AIC1578
R3
12K
R4
3K9
C2
0.1
F
+V
IN
6.4~18V
+V
OUT
, 5V
Rs
*
+
C4
470
F
D1
GS SS32
+
C1
100
F
<15V
L1
33
H
R6
1M
Q1
CEM44
R7
**
L
f
V
2
)
V
V
(
V
I
I
S
IN
O
IN
O
MAX
,
O
P
-
+
=
2
O
O
IN
MAX
,
O
S
IN
S
IN
P
P
TH
S
V
V
V
LI
f
V
2
L
f
V
1
.
0
I
mV
50
I
V
R
-
+
=
=
=
V
IN
: Input voltage
V
OUT
: Output voltage
f
S
: Working frequency
L= Inductor value
I
O,MAX
: Maximum Output current
V
TH
: Current Limit Sense Threshold
**V
IN
>15V, R7=15
V
IN
15V, R7=0
DC/DC Buck Converter
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ORDERING INFORMATION
PIN CONFIGURATION
SO-8
TOP VIEW
DRI
CS+
DUTY
FB
CS-
GND
VIN
SHDN
1
3
4
2
8
6
5
7
AIC15 78C XXX
PACKING TYPE
TR: TAPE & REEL
TB: TUBE
PACKAGING TYPE
S: SMALL OUTLINE
N: PLASTIC DIP
Example: AIC1578CSTR
in SO-8 Package & Taping & Reel
Packing Type
(CN is not available in TR packing)
AIC1578
3
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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
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TEST CIRCUIT
Refer to TYPICAL APPLICATION CIRCUIT.
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ELECTRICAL CHARACTERISTICS
(V
IN
= 13V, T
A
=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
4
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TYPICAL PERFORMANCE CHARACTERISTICS
Fig. 1 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
T
A
=
27
C
Frequency
Frequency (KHz)
0
50
10
15
20
25
30
35
Temperature (
C)
Fig. 2 Duty Cycle vs.Temperature
Duty Cycle (%)
V
IN
=5V
0
20
40
60
80
60
65
70
75
80
85
90
V
IN
=20V
V
IN
=13V
Temperature (
C)
Fig. 3 Frequency vs. Temperature
Frequency (KHz)
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
)
Fig. 4 Duty Cycle vs. R
DUTY
Duty Cycle (%)
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.
Circuit.
V
IN
(V)
Fig. 5 Shutdown Current vs. V
IN
Shutdown Current (
A)
20
4
6
8
10
12
14
16
18
0
5
10
15
20
T
A
=0
C
T
A
=25
C
T
A
=70
C
V
IN
(V)
Fig. 6 Quiescent Current vs. V
IN
Quiescent Current (
A)
4
6
8
10
12
14
16
18
20
60
70
80
90
100
110
T
A
= 25
C
T
A
= 70
C
T
A
= 0
C
AIC1578
5
n
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
-
+
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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. R
DUTY
must
be over 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
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 voltage.
Connecting a resistor R1 to
converter output node and a
resistor R2 to ground yields the
output voltage:
V
OUT
=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.
PIN 7: CS- - Current sense
comparator
inverting input. This pin voltage
should go over 2V but not to
exceed VIN voltage.
PIN 8: CS+ - Current sense comparator non-
inverting input. This pin voltage
should go over 2V but not to
exceed V
IN
voltage.
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