ST735S
ST735T
300kHz, -5V/ADJ INVERTING, NEGATIVE OUTPUT
CURRENT-MODE PWM REGULATOR
s
s
s
s
s
s
s
s
s
s
s
CONVERTS +4.0V TO + 6.2V INPUT TO -5V
OUTPUT (735S) OR +3.5V TO + 9.0V TO A
NEGATIVE ADJUSTABLE OUTPUT (735T)
1W GUARANTEED OUTPUT POWER
72% TYPICAL EFFICIENCY
0.8mA QUIESCENT CURRENT
1µA SHUTDOWN MODE
300KHZ FIXED FREQUENCY OSCILLATOR
CURRENT MODE PWM CONVERTER
LOW NOISE AND JITTER
SOFT START
SIMPLE APPLICATION CIRCUIT
UNDERVOLTAGE LOCKOUT (735S)
DIP-8
SO-8
DESCRIPTION
The ST735S/ST735T is a Bi-CMOS, inverting
switch mode DC-DC regulator with internal Power
MOSFET that generates a fixed -5V (S version) or
a negative adjustable (T version) output voltage
from a 4V (3.5V for the 735T) to 6.2V input voltage
(9V for the 735T); is guaranteed an output current
of 200mA for inputs greater than 4.5V. The
quiescent current for this device is typically of
SCHEMATIC DIAGRAM
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0.8mA and, in shutdown mode it is reduced to
1µA.
These power-conserving features, along with high
efficiency and applications circuits, thaT lend itself
to minaturization, make the ST735S/ST735T
excellent in a broad range of on-card, HDD and
portable equipment applications. These device
employ a high performance current mode pulse
with modulation (PWM) control scheme to provide
tight output voltage regulation and low noise. The
fixed frequency oscillator is factory trimmed to
300KHz, allowing for easy noise filtering. The
regulator in production is tested to guarantee an
output accuracy within ±5% over all specified
conditions.
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October 2002
1/11
ST735S/ST735T
ABSOLUTE MAXIMUM RATINGS
Symbol
V
IN
V
IN
SHDN
V
LX
V
FB
V
OUT
I
LX
P
tot
T
stg
T
op
Parameter
DC Input Voltage (V
IN
to GND) for ST735S
DC Input Voltage (V
IN
to GND) for ST735T (Note 1)
Shutdown Voltage (SHDN to GND)
Switch Voltage (Lx to V
IN
)
Feedback Voltage (V
OUT
to GND)
Output Voltage (V
OUT
to GND)
Other Input Voltage (SS, CC to GND)
Peack Switch Current
Power Dissipation at T
j
= 70°C
Storage Temperature Range
Operating Junction Temperature Range
DIP-8
SO-8
Value
-0.3 to +7
-0.3 to +11
-0.3 to V
IN
+0.3
-12.5 to +0.3
-11 to +0.3
-11 to +0.3
-0.3 to V
+
+0.3
2
725
470
-55 to +150
-40 to +125
Unit
V
V
V
V
V
V
V
A
mW
°C
°C
Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition is
not implied.
Note 1: The input to output differential voltage is limited to V
IN
+|V
OUT
|<12.7V
THERMAL DATA
Symbol
R
thj-case
Parameter
Thermal Resistance Junction-case
DIP-8
2
CONNECTION DIAGRAM
(top view)
PIN DESCRIPTION
O
so
b
1
2
3
4
5
6
7
8
Pin N°
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P
uc
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t(
bs
-O
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SO-8
8
s)
t(
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Unit
°C/W
Symbol
SHDN
V
REF
SS
CC
V
OUT
GND
LX
V
IN
Reference Output Voltage
Soft Start
Compensation Input
Negative Output Voltage
Name and Function
SHUT-DOWN Control (V
CC
=ON GND=Shutdown
Ground
Switch Output
Positive Supply - Voltage Input
2/11
ST735S/ST735T
ORDERING CODES
TYPE
ST735S
ST735T
DIP-8
ST735SCN
ST735TCN
SO-8
ST735SCD
ST735TCD
SO-8 (T&R)
ST735SCD-TR
ST735TCD-TR
TYPICAL APPLICATION CIRCUIT
NOTE:
1) All capacitors are X7R ceramic
2) C
5
can be omitted if are used higher values for the input and output capacitors (suggested C
2
=47µF, C
1
=100µF).
3) R
1
and R
2
must be placed is ST735T applications only. Their values are calculated by the following formula R
2
=(|V
OUT
|/V
REF
)xR
1
. For R
1
can be chosen any value between 2kΩ and 20kΩ
APPLICATION CIRCUIT
To achieve the best performances from switching
power supply topology, particular care to layout
drawing is needed, in order to minimize EMI and
obtain low noise. Moreover, jitter free operation
ensures the full device functionality. Layout design
proposed on demoboard helps to lower the
developing time. Wire lengths must be minimized,
PRINTED DEMOBOARD
(not in scale)
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filter and bypass capacitors must be low ESR
type, placed as close as possible to the integrated
circuit. The 4.7µF (or 6.8µF) inductor must be
chosen built on a core, taking care that saturation
current should be higher than the peak LX switch
current. See the Peak Inductor Current vs Output
Current graph.
3/11
ST735S/ST735T
ELECTRICAL CHARACTERISTICS OF ST735S
(Refer to test circuit, V
IN
=5V, C
IN
= 4.7µF, C
OUT
= 10µF
all X7R ceramic, L = 4.7µH (Note1) , I
OUT
=0mA, T
amb
= -40 to 125°C, unless otherwise specified. Typical
value are referred at T
amb
= 25°C)
Symbol
V
IN
V
OUT
Parameter
Input Voltage
Output Voltage
V
IN
= 4.5V to 6.2V I
OUT
= 0 to 200mA
T
amb
= -40 to 125
°C
V
IN
= 4.0V to 6.2V I
OUT
= 0 to 175mA
T
amb
= -40 to 125
°C
I
OUT
Output Current
V
IN
= 4.5V to 6.2V T
J
= 0 to 125
°
C
V
IN
= 4.5V to 6.2V I
OUT
= 0 to 175mA
T
amb
= -40 to 125
°C
V
IN
= 4.0V
I
SUPPLY
I
SC
I
PEAK
V
LO
∆V
OUT
∆V
OUT
V
REF
∆V
REF
R
DSON
I
LEAK
I
SH
V
IL
V
IH
f
OSC
½
R
CC
Supply Current
Short Circuit Current
LX Max Peak Current
Undervoltage Lock-out
Line Regulation
Load Regulation
Reference Voltage
Reference Drift
LX ON Voltage
LX Leakage Current
Shutdown Pin Current
Shutdown Input Low
Threshold
Shutdown Input High
Threshold
Maximum Oscillator
Frequency
Efficency
V
DS
= 10V
V
IN
= 4.0V to 6.2V
I
OUT
= 0 to 200mA
T
amb
= 25
°
C (Note 3)
T
amb
= -40 to 125
°
C
I
STANDBY
Standby Current
V
SHDN
= 0V
V
IN
= 5V
(Note 2)
V
OUT
= -5V
Includes Switch Current
Test Conditions
Min.
4
-5.25
-5.25
200
175
175
0.8
1
0.9
1.5
3.5
1.6
10
-5
-5
275
Typ.
Max.
6.2
-4.75
-4.75
Unit
V
V
V
mA
mA
mA
mA
µA
A
A
Compensation Pin
Impedance on CC Pin
Note 1: Utilize of 6.8µH permits to reach higher current capability at the same operating conditions
Note2: Guaranteed by design, but not tested in production
Note3 : Tested at I
VREF
= 125µA
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0.1
50
0.5
1
s)
t(
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4
V
%/V
V
0.003
%/mA
ppm/°C
Ω
µA
1
0.25
µA
V
V
1.225
2
300
72
7.5
KHz
%
KΩ
I
OUT
= 100mA
4/11
ST735S/ST735T
ELECTRICAL CHARACTERISTICS OF ST735T
(Refer to test circuit, V
IN
=5V, C
IN
= 4.7µF, C
OUT
= 10µF
all X7R ceramic, L = 4.7µH (Note1) , I
OUT
=0mA, V
O
adjusted to -5V, T
amb
= -40 to 125°C, unless otherwise
specified. Typical value are referred at Tamb= 25°C)
Symbol
V
IN
V
O
Parameter
Input Voltage
Output Voltage
V
IN
= 4.5V to 6.2V I
OUT
= 0 to 200mA
T
amb
= -40 to 125
°C
V
IN
= 4.0V to 6.2V I
OUT
= 0 to 175mA
T
amb
= -40 to 125
°C
I
O
Output Current
V
IN
= 4.5V to 6.2V T
amb
= 0 to 125
°
C
V
IN
= 4.5V to 6.2V I
OUT
= 0 to 175mA
T
amb
= -40 to 125
°C
V
IN
= 4.0V
I
SUPPLY
I
SC
I
PEAK
V
LO
∆V
OUT
∆V
OUT
V
REF
∆V
REF
R
DSON
I
LEAK
I
SH
V
IL
V
IH
f
OSC
½
R
CC
Supply Current
Short Circuit Current
LX Max Peak Current
Undervoltage Lock-out
Line Regulation
Load Regulation
Reference Voltage
Reference Drift
LX ON Voltage
LX Leakage Current
Shutdown Pin Current
Shutdown Input Low
Threshold
Shutdown Input High
Threshold
Maximum Oscillator
Frequency
Efficency
V
DS
= 10V
V
IN
= 4.0V to 6.2V
I
OUT
= 0 to 200mA
T
amb
= 25
°
C (Note 3)
T
amb
= -40 to 125
°
C
I
STANDBY
Standby Current
V
SHDN
= 0V
V
IN
= 5V
(Note 2)
V
OUT
= -5V
Includes Switch Current
Test Conditions
Min.
3.5
-5.25
-5.25
200
175
175
0.8
1
0.9
1.5
3.5
1.6
10
-5
-5
275
Typ.
Max.
9
-4.75
-4.75
Unit
V
V
V
mA
mA
mA
mA
µA
A
A
Compensation Pin
Impedance on CC Pin
Note 1: Utilize of 6.8µH permits to reach higher current capability at the same operating conditions
Note2: Guaranteed by design, but not tested in production
Note3 : Tested at I
VREF
= 125µA
O
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t(
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-O
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P
od
0.1
50
0.5
1
s)
t(
uc
4
V
%/V
V
0.003
%/mA
ppm/°C
Ω
µA
1
0.25
µA
V
V
1.225
2
300
72
7.5
KHz
%
KΩ
I
OUT
= 100mA
5/11
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