SS431/G
Adjustable Precision Shunt Regulator
FEATURES
Low voltage operation (2.5V)
Adjustable output voltage from V
O
= V
REF
to 18V
Wide operating current range from 0.4mA to 100mA
Low dynamic output impedance 0.5Ω max.
ESD rating is 5.5kV (per MIL-STD 883D)
Pb-free lead finish available.
DESCRIPTION
The SS431 is a low-voltage three-terminal adjustable shunt
regulator with a guaranteed thermal stability over the applicable
temperature range. The output voltage can be set to any value
between V
REF
(approximately 2.5V) to 18V with two external
resistors (see application circuit). This device has a typical output
impedance of 0.2 ohms. Active output circuitry provides very sharp
turn-on
characteristics,
making
this
device
an
excellent
replacement for Zener diodes in many applications.
The SS431 is characterized for operation from 0°C to 105°C,
and three package options (SOT-23, SOT-89, and TO-92) allow
the designer the opportunity to select the proper package for his
application.
The SS431 is available with a Pb-free lead finish
- order as SS431Gxx.
APPLICATIONS
Linear Regulators
Adjustable Supplies
Switching Power Supplies
Battery Operated Computers
Instrumentation
Computer Disk Drives
PIN CONFIGURATION
SOT-23 (Top view)
BLOCK DIAGRAM
Cathode
Ref
2
Cathode
Anode
3
1
+
Reference
-
Vref
SOT-89 (Top view)
Anode
3
2
1
Cathode
Anode
Reference
TO-92 (Top view)
3
Cathode
2
Anode
1
Reference
SYMBOL
Cathode
Ref.
Anode
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SS431/G
ABSOLUTE MAXIMUM RATINGS over ambient temp. range.
Parameter
Symbol
θ
Maximum
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Units
ELECTRICAL CHARACTERISTICS
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≤'-
∆
∆
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%
µ
µ
µ
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SS431/G
TYPICAL PERFORMANCE CHARACTERISTICS
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SS431/G
TEST CIRCUITS
APPLICATION INFORMATION
V
MAX
V
DEV
= V
MAX
-V
MIN
V
MIN
Where:
T
2
−
T
1
=full temperature change.
αV
REF
can be positive or negative depending on
whether the slope is positive or negative.
Example: V
DEV
= 7.0mV, V
REF
= 2495mV,
T
2
−
T
1
= 105°C, slope is negative.
α
V
REF
=
T
1
TEMPERATURE
T
2
7.0mV
106
2495mV
105
°
C
= −
27ppm/
°
C
Deviation of reference input voltage, V
DEV
, is defined as
the maximum variation of the reference input voltage
over the full temperature range.
The average temperature coefficient of the reference in-
put voltage,
αV
REF
is defined as:
Note 4.
The dynamic output impedance, Rz, is de-
fined as:
R
Z
=
∆
V
Z
∆
I
Z
6
V
MAX
- V
MIN
6
V
DEV
±
±
10
10
ppm
V
REF
(at 25
°
C)
V
REF
(at 25
°
C)
=
∆
V
REF
=
T2
−
T1
T2
−
T1
°
C
When the device is programmed with two external re-
sistors, R1 and R2, (see Fig. 2), the dynamic output
impedance of the overall circuit, is defined as:
r
z
=
∆
V
≅
Rz
1
+
R1
R2
∆
I
[ ]
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SS431/G
APPLICATION EXAMPLES
V
IN
R1
R
CL
I
OUT
V
IN
SS431
SS431
R1
R
S
I
OUT
=V
REF
/ R
CL
Current Limiter or Current Source
I
OUT
=V
REF
/R
S
Constant-Current Sink
V
IN
R
IN
R3
R1
V
OUT
V
IN
FUSE
R1
R3
V
OUT
SS431
R2
SS431
R2
V
OUT
≅
(1+R1/R2) x V
REF
Higher-Current Shunt Regulator
V
LIMIT
≅
(1+R1/R2) x V
REF
Crow Bar
V
IN
R1A
R1B
R3
SS431
Output turns ON when
Low Limit <V
IN
< High Limit
C1
SS431
R2A
R2B
+
R4
R5
V
BE
Low Limit≅ V
REF
( 1+ R1B/ R2B )+ V
BE
High Limit
≅
V
REF
( 1+ R1A/ R2A )
Over-Voltage/Under-Voltage Protection Circuit
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