LT1431
Programmable Reference
FEATURES
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DESCRIPTIO
Guaranteed 0.4% Initial Voltage Tolerance
0.1Ω Typical Dynamic Output Impedance
Fast Turn On
Sink Current Capability, 1mA to 100mA
Low Reference Pin Current
Available in N8, S8 or 3-Lead TO-92 Z Packages
APPLICATIO S
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Linear Regulators
Adjustable Power Supplies
Switching Power Supplies
The LT
®
1431 is an adjustable shunt voltage regulator with
100mA sink capability, 0.4% initial reference voltage tol-
erance and 0.3% typical temperature stability. On-chip
divider resistors allow the LT1431 to be configured as a 5V
shunt regulator, with 1% initial voltage tolerance and
requiring no additional external components. By adding
two external resistors, the output voltage may be set to any
value between 2.5V and 36V. The nominal internal current
limit of 100mA may be decreased by including one exter-
nal resistor.
A simplified 3-pin version, the LT1431CZ/LT1431IZ, is
available for applications as an adjustable reference and is
pin compatible with the TL431.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
+
Isolated 5V Regulator
5V
+
V
IN
SWITCHING
REGULATOR
2.5025
2.5000
–
V
REF
(V)
2.4975
2.4950
2.4925
2.4900
2.4875
–50 –25
5V
R
TOP
V
+
COMP
COLL
REF
+
g
m
=
4mA/V
R
MID
–
2.5V
LT1431
GND-S
GND-F
LT1431 • TA01
U
V
REF
vs Temperature
50
25
75
0
TEMPERATURE (°C)
100
125
LT1431 • TA01b
U
U
1413fc
1
LT1431
ABSOLUTE
AXI U
RATI GS
V
+
, V
COLLECTOR
....................................................... 36V
V
COMP
, R
TOP
, R
MID
, V
REF
.......................................... 6V
GND-F to GND-S .................................................... 0.7V
Ambient Temperature Range
LT1431M
(OBSOLETE)
................... – 55°C to 125°C
LT1431I ............................................ – 40°C to 85°C
LT1431C .............................................. 0°C TO 70°C
PACKAGE/ORDER I FOR ATIO
TOP VIEW
COLLECTOR 1
COMP 2
V
+
3
R
TOP
4
N8 PACKAGE
8-LEAD PDIP
8
7
6
5
REF
R
MID
GND-F
GND-S
ORDER PART
NUMBER
LT1431CN8
LT1431IN8
LT1431CS8
LT1431IS8
S8 PART MARKING
1431
1431I
LT1431MJ8
BOTTOM VIEW
S8 PACKAGE
8-LEAD PLASTIC SO
T
J MAX
= 100°C,
θ
JA
= 130°C/W (N)
T
J MAX
= 100°C,
θ
JA
= 170°C/W (S)
T
J MAX
= 150°C,
θ
JA
= 100°C/W (J)
OBSOLETE PACKAGE
Consider the N8 or S8 for Alternate Source
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
REF
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. I
K
= 10mA unless otherwise specified (Note 2)
PARAMETER
Reference Voltage
CONDITIONS
V
KA
= 5V, I
K
= 2mA, (Note 3)
V
KA
= 5V, I
K
= 2mA
I
K
= 2mA, V
KA
= 3V to 36V
V
KA
= 5V, T
A
= 25°C
V
KA
= V
REF
to 36V
V
KA
= 36V, V
REF
= 0V
V
COLL
= 36V, V
+
= 5V, V
REF
= 2.4V
V
KA
= V
REF
, I
K
= 1mA to 100mA, f
≤
1kHz
V
KA
= V
REF
+ 50mV
Internal Divider Used, I
K
= 2mA
●
∆V
REF
/∆T
Reference Drift
∆V
REF
/∆V
KA
Voltage Ratio, Reference to
Cathode (Open-Loop Gain)
|I
REF
|
Reference Input Current
I
MIN
|I
OFF
|
|I
LEAK
|
|Z
KA
|
I
LIM
Minimum Operating Current
Off-State Cathode Current
Off-State Collector Leakage Current
Dynamic Impedance
Collector Current Limit
5V Reference Output
2
U
U
W
W W
U
W
(Note 1)
JunctionTemperature Range
LT1431M
(OBSOLETE)
................... – 55°C to 150°C
LT1431I .......................................... – 40°C to 100°C
LT1431C ............................................. 0°C to 100°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
ORDER PART
NUMBER
LT1431CZ
LT1431IZ
REF ANODE
CATHODE
Z PACKAGE
3-LEAD TO-92 PLASTIC
T
J MAX
= 100°C,
θ
JA
= 150°C/W
LT1431M/I
MIN TYP MAX
LT1431C
MIN TYP MAX UNITS
2.490 2.500 2.510 2.490 2.500 2.510
V
2.465
2.535 2.480
2.520
V
●
50
30
ppm/°C
●
0.2 0.5
0.2 0.5
mV/V
1.0
0.2 1.0
1.5
1.2
0.6 1.0
0.6 1.0
1
1
●
15
2
1
1
●
5
2
0.2
0.2
●
80
360
100
260
4.950 5.000 5.050 4.950 5.000 5.050
●
0.2
µA
µA
mA
µA
µA
µA
µA
Ω
mA
V
1413fc
LT1431
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
V
KA
is the cathode voltage of the LT1431CZ/IZ and corresponds to
V
+
of the LT1431CN8/IN8/CS8/IS8. I
K
is the cathode current of the
LT1431CZ/IZ and corresponds to I(V
+
) + I
COLLECTOR
of the LT1431CN8/
IN8/CS8/IS8.
Note 3:
The LT1431 has bias current cancellation which is effective only
for V
KA
≥
3V. A slight (≈2mV) shift in reference voltage occurs when
V
KA
drops below 3V. For this reason, these tests are not performed at
V
KA
= V
REF
.
TYPICAL PERFOR A CE CHARACTERISTICS
2.5V Reference I
K
vs V
KA
1000
900
800
700
I
K
(µA)
2.505
2.504
2.503
2.502
V
REF
(V)
500
2.500
2.499
2.498
V
REF
1.0
0.5
0
V
REF
(V)
600
I
MIN
400
300
200
100
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V
KA
(V)
LT1431 • TPC01
V
REF
and I
REF
vs Temperature
2.5025
2.5000
2.4975
V
REF
(V)
V
REF
I
LIMIT
(NORMALIZED)
2.4950
2.4925
2.4900
2.4875
–50 –25
I
REF
V
SAT
(V)
50
25
75
0
TEMPERATURE (°C)
U W
100
V
REF
and I
REF
vs V
+
3.5
3.0
2.5
2.0
1.5
V
REF
and I
REF
vs V
+
2.505
2.504
2.503
2.502
2.501
2.500
2.499
2.498
2.497
2.496
2.495
0
4
8
12 16 20 24 28 32 36 40
V
+
(V)
LT1431 • TPC03
3.5
3.0
2.5
2.0
1.5
V
REF
1.0
0.5
I
REF
0
–0.5
–1.0
–1.5
I
REF
(µA)
2.501
I
REF
(µA)
I
REF
2.497
2.496
–0.5
–1.0
2.495
–1.5
2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5
V
+
(V)
LT1431 • TPC02
I
LIMIT
vs Temperature with
External Resistor
1.00
0.66
0.33
I
REF
(µA)
COLLECTOR V
SAT
vs
Temperature vs Current
1.20
1.250
1.125
1.000
0.875
0.750
0.625
0.500
–50 –25
0.7
I
LIMIT
=
AT 25°C
R
LIM
+ 3.6
1.00
I
COLL
= 100mA
0.80
0.60
I
COLL
= 50mA
0.40
0.20
0
–50 –25
I
COLL
= 20mA
I
COLL
= 10mA
50
25
75
0
TEMPERATURE (°C)
100
125
0
–0.33
–0.66
–1.00
125
50
25
75
0
TEMPERATURE (°C)
100
125
LT1431 • TPC04
LT1431 • TPC05
LT1431 • TPC06
1413fc
3
LT1431
TYPICAL PERFOR A CE CHARACTERISTICS
Propagation Delay vs Overdrive
150
135
5V 1k
3
V
REF
±
OVERDRIVE
LT1431
5
6
1
OUTPUT
REF-TO-COLL 1k LOAD A
V
(dB)
PROPAGATION DELAY (µs)
120
105
90
75
60
45
30
15
0
0
REF-TO-COLL g
m
(µ )
OUTPUT HIGH-TO-LOW
OUTPUT LOW-TO-HIGH
50
150
100
OVERDRIVE (mV)
Transconductance and Phase
vs Frequency (Ref to Comp)
10
4
PHASE
g
m
0
–20
–40
10
3
–60
–80
3
×
10
2
REF-TO-COLL g
m
(µ )
3
×
10
3
Z
KA
(Ω)
0.8
0.6
0.4
0.2
0
100
V
COMP
(V)
0.1
100
1k
10k
100k
FREQUENCY (Hz)
I
COMP
vs V
COMP
vs V
REF
600
500
V
REF
= 5V
NOISE (nV/√Hz)
400
1000
I
COMP
(µA)
V
REF
= 4V
V
REF
= 3V
300
200
V
REF
= 2.53V
100
0
0
0.5
1.0
1.5 2.0
V
COMP
(V)
2.5
3.0
3.5
500
0
1
10
100
1k
FREQUENCY (Hz)
10k
100k
NOISE VOLTAGE (50µV/DIV)
4
U W
200
LT1431 • TPC07
Voltage Gain and Phase
vs Frequency
140
120
100
80
60
40
20
0
A
V
PHASE
180
135
90
45
0
–45
–90
–135
1k
10k
100k
FREQUENCY (Hz)
1M
–180
10M
Ω
Transconductance and Phase
vs Frequency (REF to COLL)
10
10
10
9
10
8
10
7
10
6
10
5
10
4
10
3
10
2
100
1k
10k
100k
FREQUENCY (Hz)
1M
PHASE
90
g
m
45
0
–45
–90
–135
–180
10M
PHASE (DEG)
180
135
PHASE (DEG)
250
–20
100
LT1431 • TPC08
LT1431 • TPC09
Dynamic Impedance vs Frequency
20
V
COMP
vs Temperature vs I
COLL
3.0
2.5
2.0
1.5
1.0
0.5
0
–50 –25
1.4
1.2
1.0
I
K
≤
100mA
Ω
–100
–120
1M
–140
10M
PHASE (DEG)
I
COLL
= 100mA
I
COLL
= 10mA
1k
10k
FREQUENCY (Hz)
100k
LT1431 • TPC11
50
25
75
0
TEMPERATURE (°C)
100
125
LT1431 • TPC10
LT1431 • TPC12
Noise vs Frequency
0.1Hz to 10Hz Noise
0
1
4
3
2
TIME (MINUTES)
5
6
LT1431 • TPC13
LT1431 • G14
LT1431 • TPC15
1413fc
LT1431
PI FU CTIO S
COLL (Pin 1):
Open collector of the output transistor. The
maximum pin voltage is 36V. The saturation voltage at
100mA is approximately 1V.
COMP (Pin 2):
Base of the driver for the output transistor.
This pin allows additional compensation for complex
feedback systems and shutdown of the regulator. It must
be left open if unused.
V
+
(Pin 3):
Bias voltage for the entire shunt regulator. The
maximum input voltage is 36V and the minimum to
operate is equal to V
REF
(2.5V). The quiescent current is
typically 0.6mA.
R
TOP
(Pin 4):
Top of the on-chip 5k-5k resistive divider
that guarantees 1% accuracy of operation as a 5V shunt
regulator with no external trim. The pin is tied to COLL for
self-contained 5V operation. It may be left open if unused.
See note on parasitic diodes below.
GND-S (Pin 5):
Ground reference for the on-chip resistive
divider and shunt regulator circuitry except for the output
transistor. This pin allows external current limit of the
output transistor with one resistor between GND-F (force)
and GND-S (sense).
GND-F (Pin 6):
Emitter of the output transistor and sub-
strate connection for the die.
R
MID
(Pin 7):
Middle of the on-chip resistive divider string
between R
TOP
and GND-S. The pin is tied to REF for self-
contained 5V operation. It may be left open if unused.
REF (Pin 8):
Control pin of the shunt regulator with a 2.5V
threshold. If V
+
> 3V, input bias current cancellation
reduces I
B
to 0.2µA typical.
COMP, R
TOP
, R
MID
, and REF have static discharge protec-
tion circuits that must not be activated on a continuous
basis. Therefore, the absolute maximum DC voltage on
these pins is 6V, well beyond the normal operating condi-
tions.
As with all bipolar ICs, the LT1431 contains parasitic
diodes which must not be forward biased or else anoma-
lous behavior will result. Pin conditions to be avoided are
R
TOP
below R
MID
in voltage and any pin below GND-F in
voltage (except for GND-S).
The following pin definitions apply to the Z package.
CATHODE:
Corresponds to COLL and V
+
tied together.
ANODE:
Corresponds to GND-S and GND-F tied together.
REF:
Corresponds to REF.
BLOCK DIAGRA
W
U
U
U
R
TOP
4
V
+
3
COMP
2
COLLECTOR
1
5k
REF
8
+
g
m
=
4mA/V
R
MID
7
–
5k
2.5V
LT1431 • BD01
5
GND-SENSE
6
GND-FORCE
1413fc
5
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