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October 2002
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CONVERTS +4.0V TO + 6.2V INPUT TO -5V
OUTPUT (735S) OR +3.5V TO + 9.0V TO A
NEGATIVE ADJUSTABLE OUTPUT (735T)
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1W GUARANTEED OUTPUT POWER
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72% TYPICAL EFFICIENCY
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0.8mA QUIESCENT CURRENT
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1A SHUTDOWN MODE
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300KHZ FIXED FREQUENCY OSCILLATOR
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CURRENT MODE PWM CONVERTER
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LOW NOISE AND JITTER
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SOFT START
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SIMPLE APPLICATION CIRCUIT
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UNDERVOLTAGE LOCKOUT (735S)
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
0.8mA and, in shutdown mode it is reduced to
1A.
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.
ST735S
ST735T
300kHz, -5V/ADJ INVERTING, NEGATIVE OUTPUT
CURRENT-MODE PWM REGULATOR
SCHEMATIC DIAGRAM
DIP-8
SO-8
ST735S/ST735T
2/11
ABSOLUTE MAXIMUM RATINGS
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
CONNECTION DIAGRAM (top view)
PIN DESCRIPTION
Symbol
Parameter
Value
Unit
V
IN
DC Input Voltage (V
IN
to GND) for ST735S
-0.3 to +7
V
V
IN
DC Input Voltage (V
IN
to GND) for ST735T (Note 1)
-0.3 to +11
V
SHDN
Shutdown Voltage (SHDN to GND)
-0.3 to V
IN
+0.3
V
V
LX
Switch Voltage (Lx to V
IN
)
-12.5 to +0.3
V
V
FB
Feedback Voltage (V
OUT
to GND)
-11 to +0.3
V
V
OUT
Output Voltage (V
OUT
to GND)
-11 to +0.3
V
Other Input Voltage (SS, CC to GND)
-0.3 to V
+
+0.3
V
I
LX
Peack Switch Current
2
A
P
tot
Power Dissipation at T
j
= 70C
DIP-8
725
mW
SO-8
470
T
stg
Storage Temperature Range
-55 to +150
C
T
op
Operating Junction Temperature Range
-40 to +125
C
Symbol
Parameter
DIP-8
SO-8
Unit
R
thj-case
Thermal Resistance Junction-case
2
8
C/W
Pin N
Symbol
Name and Function
1
SHDN
SHUT-DOWN Control (V
CC
=ON GND=Shutdown
2
V
REF
Reference Output Voltage
3
SS
Soft Start
4
CC
Compensation Input
5
V
OUT
Negative Output Voltage
6
GND
Ground
7
LX
Switch Output
8
V
IN
Positive Supply - Voltage Input
ST735S/ST735T
3/11
ORDERING CODES
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
=47
F, C
1
=100
F).
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 2k
and 20k
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,
filter and bypass capacitors must be low ESR
type, placed as close as possible to the integrated
circuit. The 4.7
F (or 6.8
F) 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.
PRINTED DEMOBOARD (not in scale)
TYPE
DIP-8
SO-8
SO-8 (T&R)
ST735S
ST735SCN
ST735SCD
ST735SCD-TR
ST735T
ST735TCN
ST735TCD
ST735TCD-TR
ST735S/ST735T
4/11
ELECTRICAL CHARACTERISTICS OF ST735S (Refer to test circuit, V
IN
=5V, C
IN
= 4.7
F, C
OUT
= 10
F
all X7R ceramic, L = 4.7
H (Note1) , I
OUT
=0mA, T
amb
= -40 to 125C, unless otherwise specified. Typical
value are referred at T
amb
= 25C)
Note 1: Utilize of 6.8
H 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
= 125
A
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
V
IN
Input Voltage
4
6.2
V
V
OUT
Output Voltage
V
IN
= 4.5V to 6.2V I
OUT
= 0 to 200mA
T
amb
= -40 to 125
C
-5.25
-5
-4.75
V
V
IN
= 4.0V to 6.2V I
OUT
= 0 to 175mA
T
amb
= -40 to 125
C
-5.25
-5
-4.75
V
I
OUT
Output Current
V
IN
= 4.5V to 6.2V T
J
= 0 to 125
C
200
275
mA
V
IN
= 4.5V to 6.2V I
OUT
= 0 to 175mA
T
amb
= -40 to 125
C
175
mA
V
IN
= 4.0V
V
OUT
= -5V
175
mA
I
SUPPLY
Supply Current
Includes Switch Current
0.8
1.6
mA
I
STANDBY
Standby Current
V
SHDN
= 0V
1
10
A
I
SC
Short Circuit Current
V
IN
= 5V
0.9
A
I
PEAK
LX Max Peak Current
(Note 2)
1.5
A
V
LO
Undervoltage Lock-out
3.5
4
V
V
OUT
Line Regulation
V
IN
= 4.0V to 6.2V
0.1
%/V
V
OUT
Load Regulation
I
OUT
= 0 to 200mA
0.003
%/mA
V
REF
Reference Voltage
T
amb
= 25
C (Note 3)
1.225
V
V
REF
Reference Drift
T
amb
= -40 to 125
C
50
ppm/C
R
DSON
LX ON Voltage
0.5
I
LEAK
LX Leakage Current
V
DS
= 10V
1
A
I
SH
Shutdown Pin Current
1
A
V
IL
Shutdown Input Low
Threshold
0.25
V
V
IH
Shutdown Input High
Threshold
2
V
f
OSC
Maximum Oscillator
Frequency
300
KHz
Efficency
I
OUT
= 100mA
72
%
R
CC
Compensation Pin
Impedance on CC Pin
7.5
K
ST735S/ST735T
5/11
ELECTRICAL CHARACTERISTICS OF ST735T (Refer to test circuit, V
IN
=5V, C
IN
= 4.7
F, C
OUT
= 10
F
all X7R ceramic, L = 4.7
H (Note1) , I
OUT
=0mA, V
O
adjusted to -5V, T
amb
= -40 to 125C, unless otherwise
specified. Typical value are referred at Tamb= 25C)
Note 1: Utilize of 6.8
H 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
= 125
A
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
V
IN
Input Voltage
3.5
9
V
V
O
Output Voltage
V
IN
= 4.5V to 6.2V I
OUT
= 0 to 200mA
T
amb
= -40 to 125
C
-5.25
-5
-4.75
V
V
IN
= 4.0V to 6.2V I
OUT
= 0 to 175mA
T
amb
= -40 to 125
C
-5.25
-5
-4.75
V
I
O
Output Current
V
IN
= 4.5V to 6.2V T
amb
= 0 to 125
C
200
275
mA
V
IN
= 4.5V to 6.2V I
OUT
= 0 to 175mA
T
amb
= -40 to 125
C
175
mA
V
IN
= 4.0V
V
OUT
= -5V
175
mA
I
SUPPLY
Supply Current
Includes Switch Current
0.8
1.6
mA
I
STANDBY
Standby Current
V
SHDN
= 0V
1
10
A
I
SC
Short Circuit Current
V
IN
= 5V
0.9
A
I
PEAK
LX Max Peak Current
(Note 2)
1.5
A
V
LO
Undervoltage Lock-out
3.5
4
V
V
OUT
Line Regulation
V
IN
= 4.0V to 6.2V
0.1
%/V
V
OUT
Load Regulation
I
OUT
= 0 to 200mA
0.003
%/mA
V
REF
Reference Voltage
T
amb
= 25
C (Note 3)
1.225
V
V
REF
Reference Drift
T
amb
= -40 to 125
C
50
ppm/C
R
DSON
LX ON Voltage
0.5
I
LEAK
LX Leakage Current
V
DS
= 10V
1
A
I
SH
Shutdown Pin Current
1
A
V
IL
Shutdown Input Low
Threshold
0.25
V
V
IH
Shutdown Input High
Threshold
2
V
f
OSC
Maximum Oscillator
Frequency
300
KHz
Efficency
I
OUT
= 100mA
72
%
R
CC
Compensation Pin
Impedance on CC Pin
7.5
K
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