SS6578
High-Efficiency, Step-Down DC/DC Controller
FEATURES
4V to 18V 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 SS6578 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 SS6578 delivers 10mA to 2A
of output current with 87%~93% efficiency at
APPLICATIONS
•
Notebook 5V/3.3V Main Power
•
Step-Down DC/DC Controller Modules.
•
Constant-Current Source for Battery Chargers.
V
IN
=9V, V
OUT
=5V condition. A current-sense
comparator with both inverting and non-inverting
inputs uncommitted is included to provide the
crucial function of either current-limit protection
or constant-output current control. When the
SS6578 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 90µA and can be reduced to 8µA in
shutdown mode. The switching frequency range
of around 90 kHz to 280 kHz allows small size
switching components, which are ideal for battery
powered portable equipment.
ORDERING INFORMATION
SS6578CXXX
Packing
TR: Tape and reel
TB: Tubes
Packaging
S: SO-8
N: PDIP-8
PIN CONFIGURATION
SO-8
VIN
DUTY
SHDN
FB
TOP VIEW
1
2
3
4
8 CS+
7 CS-
6 DRI
5 GND
Example: SS6578CSTR
à
in SO-8 package, shipped in tape and reel packing
(PDIP-8 is only available in tubes)
Rev.2.02 4/06/2004
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SS6578
TYPICAL APPLICATION CIRCUIT
+V
IN
6.4~18V
+V
OUT
, 5V
* Rs
L1
33µH
+
R3
12K
R4
3K9
Q1
D1
GS SS32
C4
470µF
1
R6
+
C1
100µF
C2
0.1µF
1M
<15V
2
3
4
VIN
DUTY
SHDN
FB
CS+
CS-
DRI
GND
8
7
6
5
R7
**
U1 SS6578
I
P
=
I
O,MAX
+
R
S
=
V
O
( V
IN
−
V
O
)
2V
IN
×
f
S
×
L
V
TH
50mV
0.1V
IN
f
S
L
=
=
I
P
I
P
2V
IN
f
S
LI
O,MAX
+
V
IN
V
O
−
V
O
2
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=15Ω
V
IN
≤15V,
R7=0Ω
DC/DC Buck Converter
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 TYPICAL APPLICATION CIRCUIT.
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SS6578
ELECTRICAL CHARACTERISTICS
(VIN= 13V, TA=25°C, unless otherwise 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
V
CS+
= 13V
50
0.8
V
SHDN
< 15V
V
DUTY
= V
IN
V
DUTY
= V
IN
71
225
V
FB
= 1.5V
V
SHDN
= 0V
1.16
CONDITIONS
MIN.
4
90
8
1.22
16
11
70
1.5
90
2.4
1
TYP.
MAX.
20
160
20
1.28
UNIT
V
µA
µA
V
Ω
Ω
mV
V
µA
%
KHz
SHDN
Pin Leakage Current
Duty Cycle
Oscillator Frequency
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SS6578
TYPICAL PERFORMANCE CHARACTERISTICS
90
35
90
T
A
= 27°C
85
80
Duty
Frequency
30
0
25
20
15
10
50
0
20
85
Frequency (KHz)
V
IN
=5V
Duty Cycle (%)
80
Duty (%)
75
70
65
60
55
4
6
8
10
12
14
16
18
75
V
IN
=13V
70
65
V
IN
=20V
60
0
Fig. 1
V
IN
( V)
Frequency & Duty Cycle vs. V
IN
Temperature (
°
C)
Fig. 2 Duty Cycle vs.Temperature
20
40
60
80
10
290
V
IN
=5V
V
IN
=20V
90
Frequency (KHz)
240
Duty Cycle (%)
190
V
IN
=13V
80
V
IN
=10V
V
IN
=15V
140
V
IN
=5V
70
V
IN
=20V
R
DUTY
refer to Typ. App.
Circuit.
1
2
R
DUTY
(MΩ)
3
4
90
0
10
20
30
40
50
60
70
Temperature (
°
C)
Fig. 3 Frequency vs. Temperature
60
0
Fig. 4 Duty Cycle vs. R
DUTY
20
110
Shutdown Current (µA)
15
T
A
=25°C
T
A
=0°C
10
Quiescent Current (µA)
100
T
A
= 0°C
90
T
A
= 25°C
80
T
A
= 70°C
5
T
A
=70°C
70
0
4
6
8
10
12
14
16
18
20
60
4
6
8
10
12
14
16
18
20
V
IN
(V)
Fig. 5 Shutdown Current vs. V
IN
Fig. 6
V
IN
(V)
Quiescent Current vs. V
IN
Rev.2.02 4/06/2004
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SS6578
BLOCK DIAGRAM
Current Limit Comparator
VIN
1
+
70mV
8
CS+
-
DUTY
2
PFM
OSC
VIN
LATCH
7
CS-
SHDN
3
-
+
Error
Comparator
1.22V
Reference
Voltage
Output
Driver
6
DRI
FB
4
5
GND
PIN DESCRIPTIONS
PIN 1: VIN
- Input supply voltage - a range of
4V to 18V is recommended.
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.
- Current-sense
comparator
inverting input. This pin voltage
should go over 2V but should
not exceed VIN 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 over 1MΩ 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 pin is held
high.
PIN 4: FB
- Feedback comparator input, to
compare the feedback voltage
with the internal reference voltage.
PIN 7: CS-
PIN 8: CS+ - Current
sense
comparator
non-inverting input. This pin
voltage should go over 2V but
should not exceed V
IN
voltage.
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