NIKO-SEM
2.5V Low-Voltage Adjustable
Precision Shunt Regulator
FEATURES
L431
GENERAL DESCRIPTION
The L431 is a three-terminal adjustable shunt
regulator utilizing an accurate 2.5V band-gap
reference. The output voltage can be set to any
value between 2.5V (V
REF
) to 29V with two
external resistors as shown in the typical
application circuit. The device exhibit a wide
operating current range of 0.4 to 100 mA with a
typical dynamic impedance of 0.25Ω. The cha-
racteristics of these reference make it exce-
llent replacements for zener diodes in many
applications such as digital voltmeters, power
supplies, and op amp circuitry. The 2.5V volt
reference makes it convenient to obtain a
stable reference from 5.0V logic supplies.
The L431 shunt regulator is available in three
voltage tolerances (0.5%, 1.0% and 2%) and
three package options (TO-92, SOT-23-3,
SOT-23-5 and SOIC-8).
Internal amplifier with 70 mA capability
Programmable output voltage to 29V
0.25Ωtypical output impedance
Pin to pin compatible with TL431, LM431
, SC431 & AS431
Trimmed band-gap design 0.5%, 1.0%
and 2% with three package options
Low cost solution
APPLICATIONS
Linear regulator controller
Precision voltage reference
Switching power supplies
Battery operating equipment
Instrumentation
PCs, Computer disk drives
SYMBOL & BLOCK DIAGRAM
Cathode (K)
Reference
(R)
+
Cathod
(K)
Reference (R)
-
2.5 Vref
Anode (A)
Anode (A)
SYMBOL
FUNCTIONAL BLOCK DIAGRAM
1
JAN-08-Y02
NIKO-SEM
2.5V Low-Voltage Adjustable
Precision Shunt Regulator
L431
ABSOLUTE MAXIMUM RATINGS
PARAMETER
Cathode-Anode Reverse Breakdown Voltage - V
KA
Anode-Cathode Forward Current - I
AK
Reference Input Current - I
REF
Storage Temperature Range - T
STG
Junction Temperature - T
J
Lead Temperature (Soldering, 10 Seconds) - T
L
Continuous Power at 25 °C - P
D
TO-92
SOIC-8
SOT-23
VALUE
30V
70 mA
10 mA
-65 to +150 °C
150 °C
300 °C
700 mW
650 mW
200 mW
RECOMMENDED CONDITIONS
Parameter
Cathode Voltage (V
KA
)
Cathode Current (I
K
)
Rating
V
REF
to 29V
10 mA
TYPICAL THERMAL RESISTANCES
Package
TO-92
SOIC-8
SOT-23
Typ. Derating
θ
JA
θ
JC
160 °C/W 80 °C/W
6.3 mW/°C
175 °C/W 45 °C/W
5.7 mW/°C
575 °C/W 150 °C/W
1.7 mW/°C
ELECTRICAL SPECIFICATIONS
(Ambient temperature must be derated base on power dissipation and package thermal characteristics. The conditions are: V
KA
= V
REF
and
I
K
= 10 mA unless otherwise stated)
PARAMETER
Reference Voltage
∆V
REF
with Temp.
Ration of Change in V
REF
to
Cathode Voltage
Reference Input Current
I
REF
Temp. Deviation
Min. I
K
for Regulation
Off State Leakage
Dynamic Output Impedance
TEST CONDITIONS
T
A
= 25 °C, L431 (0.5%)
T
A
= 25 °C, L431 (1%)
T
A
= 25 °C, L431 (2%)
V
REF
to 10V
10V to 30V
Over Temp.
V
REF
= 0V, V
KA
= 30V
f
≤
1KHz, I
K
= 1 to 70 mA
MIN
2.482
2.470
2.445
-2.7
-2.0
TEST
TYP MAX
UNITS CIRCUIT
2.495 2.507
1
2.495 2.520 V
2.495 2.550
0.07 0.2
mV/°C
1
-1.0
mV/V
2
-0.4 0.3
µA
0.7
4
2
µA
0.4
1.2
2
mA
0.4
1
1
nA
0.04 250
3
0.25 0.5
1
Ω
2
JAN-08-Y02
NIKO-SEM
2.5V Low-Voltage Adjustable
Precision Shunt Regulator
L431
TEST CIRCUITS
V
IN
V
KA
V
IN
V
KA
V
IN
V
KA
I
REF
I
K
R1
V
REF
R2
I
REF
I
K
I
K (OFF)
- TEST CIRCUIT 1 -
(V
KA
= V
REF
)
- TEST CIRCUIT 2 -
(V
KA
> V
REF
)
- TEST CIRCUIT 3 -
(OFF STATE CURRENT)
Stability Boundary Condition For Shunt Regulation
VS. Cathode Current and Load Capacitance
Test Circuit for Vka > Vref
150
Ik
3
R1
1
L431
CL
1
VBATT
2
2
R2
10K
0
1
2
3
4
5
6
Test Circuit for Vka = Vref
The areas under the curves represent conditions that may
1
150
3
1
L431
2
2
cause the device to oscillate. For curves B, C and D, R
1
and
V
BATT
were adjusted to establish the initial V
KA
and I
KA
conditions with C
L
= 0. V
BATT
and C
L
then were adjusted
to determine the ranges of stability.
Ik
CL
3
JAN-08-Y02
NIKO-SEM
2.5V Low-Voltage Adjustable
Precision Shunt Regulator
L431
Small-Signal Gain and Phase Shift
VS. Frequency
Test Circuit for Small Signal Gain and Phase
OUT
3
15K
1
1
10uF
8.25K
Ik
1
L431
2
2
232
2
GND
Cathode Current
VS. Cathode Voltage
Cathode Current
VS. Cathode Voltage
Reference Impedance
VS. Junction Temperature
Ratio of Delta Reference Voltage to Delta Cathode Voltage
VS. Junction Temperature
Δ
Vref /
Δ
Vz (-mV/V)
Δ
Vz = 3V to 30V
r
z
(
Ω
)
4
JAN-08-Y02
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