Shunt Regulator With
Open Collector Output
POWER MANAGEMENT
Description
The SC4431 is a four terminal device for regulating an
isolated power supply with output voltages down to 1.5V.
It is intended to be used as a replacement for three
terminal shunt regulators such as SC431L where the
output voltage is too low for the device to function in
conjunction with an opto-isolator. SC4431 achieves this
by having seperate supply and output pins, allowing the
output to sink current at voltages as low as 0.1V, while
the supply pin still has sufficient voltage for the device to
function. In this way, allowing for a 1.4V drop through an
opto-isolator diode, regulation down to 1.5V out can be
achieved.
The SC4431 shunt regulator is available with three
initial reference voltage accuracies (0.5%, 1.0% and
2.0%) in the space saving 5-lead SOT-23 package. The
three voltage tolerances allow the designer the
opportunity to select the proper cost/tolerance for their
application.
Lead free, fully WEEE and ROHS compliant
SC4431
Features
Open Collector output drives Optoisolator with
as little as 1.5V input voltage
Trimmed bandgap design - initial accuracies
to + 0.5%
40mA drive capability
Regulates output as low as 50mV
Wide supply voltage range - 1.5V to 15V
Low supply current - typically 110μA
Full industrial temperature range
SOT-23-5 package
Applications
Telecom Power Supplies
Opto driver for very low output voltage (1.5V)
isolated power supplies
Battery operated applications
Point of use power supplies
Typical Application Circuit
2V Output Isolated Power Supply
T1
VIN
Primary Side
Controller
Secondary Side
Rectification
and Filtering
R1
R2
5.1k
C1
2V OUT
U1
C3
SC4431
1
VCC
33nF
R3
6.34k
5
4N25
C2
22nF
OUT
4
REF
R4
10k
3
NC
2 GND
Revision June, 2014
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POWER MANAGEMENT
Absolute Maximum Rating
Parameter
Input Supply Voltage
Vcc pin current
Output Voltage
Reference Voltage
(1)
Continuous Output Current
Reference Input Current
Operating Ambient Temperature Range
Operating Junction Temperature Range
Storage Temperature Range
Thermal Impedance Junction to Ambient
Thermal Impedance Junction to Case
Power Dissipation at T
A
= 25°C
Lead Temperature (Soldering) 10 seconds
ESD Rating (Human Body Model)
Shunt Regulator With
Open Collector Output
SC4431
Symbol
V
CC
I
CC
V
OUT
V
REF
I
OUT
I
REF
T
A
T
J
T
STG
θ
J A
θ
J C
P
D
T
LEAD
ESD
Maximum
-0.5 to +16
8
-0.5 to VCC
-0.5 to +4
40
5
-40 to +85
-40 to +150
-65 to +150
256
81
475
300
2
Units
V
mA
V
V
mA
mA
°C
°C
°C
°C/W
°C/W
mW
°C
kV
(1) If Vref will be forced above 1.224V, a resistor must be placed in series with the Vcc to limit the Icc current
below 5mA.
Electrical Characteristics
Unless specified, T
A
= 25° C, V
CC
= 2V, I
OUT
= 2mA. Values in
bold
apply over full operating temperature range.
Parameter
VCC
Input Supply Voltage
Input Supply Current
Off State Input Supply Current
REF
Reference Voltage
Symbol
V
CC
I
CC
I
CC(OFF)
Test Conditions
MIN
1.5
T YP
MAX
15
200
100
150
1.231
1.243
1.236
1.250
1.250
1.261
15
20
28
36
0.5
1.0
75
100
300
400
1
10
Units
V
μ
A
μ
A
V
REF
V
REF
= V
OUT
= 1.187V, V
OUT
= 2V
110
65
V
REF
SC4431-.5, V
REF
= V
OUT
SC4431-1, V
REF
= V
OUT
SC4431-2, V
REF
= V
OUT
1.219
1.207
1.212
1.200
1.200
1.187
1.224
1.224
1.224
8
8
0.3
V
V
V
mV
mV
μ
A
Change in V
REF
due to change in
Vcc
Change in V
REF
due to change in
I
OUT
Reference Input Current
OUT
Saturation Voltage
dV
REF
/dV
CC
dV
REF
/dI
OUT
I
REF
V
CC
= 1.5V to 15V
I
OUT
= 0.1mA to 40mA
0.1mA
≤
I
OUT
≤
10mA
V
OUT(SAT)
I
OUT
= 5mA, I
CC
= 500
μ
A
V
REF
= 1.261V, I
OUT
= 32mA
50
275
0.50
mV
mV
μ
A
Off State Output Current
I
OUT(OFF)
V
REF
= 1.187V, V
OUT
= 2V
©
2003 Semtech Corp.
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Shunt Regulator With
Open Collector Output
POWER MANAGEMENT
Pin Configurations
(TOP VIEW)
SC4431
Ordering Information
Part Number
(1)(2)
SC4431CSK-X
P ackag e
SOT-23-5
Notes: (1)
Only available in tape and reel packaging.
(Suffix ‘.TRT’ e.g. SC4431CSK-X.TRT).
(2)
Where “-X” denotes initial reference voltage toler-
ance. Available options are ±0.5% (-.5), ±1% (-1) and
±2% (-2).
(SOT
(SO T-23-5)
Pin Descriptions
Pin#
1
2
3
4
5
Pin Name
VC C
GND
NC
REF
OUT
Pin Function
This is the input supply pin for the SC4431. A low ESR capacitor should be used to bypass this
pin to GND right at the IC.
Logic and power ground.
No connection.
This is connected to the non-inverting input of the error amplifier.
This is the output pin of the device, essentially an open collector.
Note: A 22nF low ESR (ceramic) capacitor is required from
this pin to GND for stable operation.
Block Diagram
Marking Information
Top Mark
4431
Bottom Mark
yyww
yyww = Datecode (Example: 9908)
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2003 Semtech Corp.
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POWER MANAGEMENT
Typical Characteristics
Vref vs Ta Iout = 2mA
1.228
1.227
1.226
1.225
Vcc=1.5V
Vcc=2V
Vcc=5V
Vcc=15V
Shunt Regulator With
Open Collector Output
SC4431
Vref vs Ta Vcc = 2V
1.236
1.234
1.232
Iout=40ma
Iout=2mA
Iout=100uA
Vref(V)
1.223
1.222
1.221
1.220
1.219
1.218
-40 -30 -20 -10
0
10
20 30
40
50
60
70
80
Ta(Deg.C.)
Vref(V)
1.224
1.230
1.228
1.226
1.224
1.222
-40 -30 -20 -10
0
10
20
30
40
50
60
70
80
Ta(Deg.C.)
Typical Vref vs Ta Io = 2mA
Icc Off vs Ta Vout = 2V
70E-6
13E-9
Typical Vref vs Ta Vcc = 2V
Iref vs Ta Vout = 2V
Icc_Off
Iref
12E-9
65E-6
11E-9
10E-9
Icc Off(A)
Iref (A)
-40 -30 -20 -10
0
10
20
30 40 50
60
70 80
60E-6
9E-9
8E-9
7E-9
55E-6
6E-9
5E-9
50E-6
Ta(Deg.C.)
4E-9
-40 -30 -20 -10
0
10
20
30 40 50
60
70 80
Ta(Deg.C.)
Typical Icc Off vs Ta Vo = 2V
Iref vs Ta Vcc = 2V
45E-9
Iout=100uA
Iout=1mA
Typical Iout vs Ta Vo = 2V
Vsat vs Ta Vcc = 2V
350
300
250
Iout=40ma
Iout=5mA
40E-9
Iout=2mA
Iout=5mA
Iout=10mA
Iout=15mA
Vsat(mV)
35E-9
Iref(A)
200
150
100
30E-9
25E-9
50
20E-9
0
0
10
20
30
40
50
60
70
80
-40 -30 -20 -10
0
10
20
30
40
50
60
70
80
Ta(Deg.C.)
-40 -30 -20 -10
Ta(Deg.C.)
Typical Iref vs Ta Vcc = 2V
©
2003 Semtech Corp.
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Typical Vsat vs Ta Vcc = 2V
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Shunt Regulator With
Open Collector Output
POWER MANAGEMENT
Typical Characteristics
3.5000
3.5000
SC4431
3.0000
3.0000
2.5000
2.5000
2.0000
2.0000
Icc(mA)
Icc(mA)
1.5000
1.5000
1.0000
1.0000
0.5000
0.5000
0.0000
0.0000
-0.5000
1.2248
1.2703
1.3048
1.7030
3.0182
-0.5000
1.2243
1.2700
1.3009
1.7073
3.0073
Vref(v)
Vcc=2V,Io=1.3mA
Vcc=5V,Io=1.3mA
Vcc=15V,Io=1.3mA
Vcc=2V,Io=2mA
Vref(v)
Vcc=5V,Io=2mA
Vcc=15V,Io=2mA
Typical Icc vs Vref, Io = 1.3mA, Ta = 25 Deg.C.
Typical Icc vs Vref, Io = 2mA, Ta = 25 Deg.C.
+VCC
J1
+Vref_Adjust
1
2
C1
10uF
R1
4k
+V adj
C3
U1
1
Io
5
R2
3.9k
C2
10uF
J2
1
2
R4
1k
J3
1
2
C4
10uF
Vref
4
Vo
C5
22nF
R5
1k
Vref
SC4431
2
Icc vs Vref Test Circuit
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2003 Semtech Corp.
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