LT1431
Programmable Reference
FeaTures
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DescripTion
The LT
®
1431 is an adjustable shunt voltage regulator
with 100mA sink capability, 0.4% initial reference voltage
tolerance 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 external resistor.
A simplified 3-pin version, the LT1431CZ/LT1431IZ, is
available for applications as an adjustable reference and
is pin compatible with the TL431.
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 J8, N8, S8 or 3-Lead TO-92 Z Packages
applicaTions
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Linear Regulators
Adjustable Power Supplies
Switching Power Supplies
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners.
Typical applicaTion
Isolated 5V Regulator
+
+
SWITCHING
REGULATOR
5V
V
IN
V
REF
vs Temperature
2.5025
2.5000
–
V
REF
(V)
5V
R
TOP
V
+
COMP
COLL
2.4975
2.4950
2.4925
REF
+
–
2.5V
LT1431
GND-S
GND-F
LT1431 TA01
g
m
=
4mA/V
2.4900
2.4875
–50 –25
R
MID
50
25
75
0
TEMPERATURE (°C)
100
125
LT1431 TA01b
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LT1431
absoluTe MaxiMuM raTings
(Note 1)
V
+
, V
COLLECTOR
..........................................................36V
V
COMP
, R
TOP
, R
MID
, V
REF
.............................................6V
GND-F to GND-S ......................................................0.7V
Ambient Temperature Range
LT1431M, LT1431MP ......................... –55°C to 125°C
LT1431I ................................................–40°C to 85°C
LT1431C ..................................................0°C TO 70°C
Junction Temperature Range
LT1431M, LT1431MP ......................... –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
pin conFiguraTion
TOP VIEW
COLLECTOR 1
COMP 2
V
+
TOP VIEW
8 REF
7 R
MID
6 GND-F
5 GND-S
COLLECTOR 1
COMP 2
V
+
8 REF
7 R
MID
6 GND-F
5 GND-S
3
3
R
TOP
4
R
TOP
4
J8 PACKAGE
8-LEAD CERDIP
T
JMAX
= 150°C,
θ
JA
= 100°C/W
TOP VIEW
COLLECTOR 1
COMP 2
V
+
3
R
TOP
4
8
7
6
5
REF
R
MID
GND-F
GND-S
N8 PACKAGE
8-LEAD PLASTIC DIP
T
JMAX
= 100°C,
θ
JA
= 130°C/W
BOTTOM VIEW
REF ANODE
CATHODE
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 170°C/W
Z PACKAGE
3-LEAD TO-92 PLASTIC
T
JMAX
= 100°C,
θ
JA
= 150°C/W
orDer inForMaTion
LEAD FREE FINISH
LT1431CN8#PBF
LT1431IN8#PBF
LT1431CS8#PBF
LT1431IS8#PBF
LT1431MPS8#PBF
LT1431MJ8#PBF
LT1431CZ#PBF
LT1431IZ#PBF
TAPE AND REEL
LT1431CN8#TRPBF
LT1431IN8#TRPBF
LT1431CS8#TRPBF
LT1431IS8#TRPBF
LT1431MPS8#TRPBF
LT1431MJ8#TRPBF
LT1431CZ#TRPBF
LT1431IZ#TRPBF
PART MARKING
LT1431 CN8
LT1431 IN8
LT1431
LT1431I
LT1431
LT1431 MJ8
LT1431 CZ
LT1431 IZ
PACKAGE DESCRIPTION
8-Lead Plastic DIP
8-Lead Plastic DIP
8-Lead Plastic SO
8-Lead Plastic SO
8-Lead Plastic SO
8-Lead CERDIP
3-Lead TO-92 Plastic
3-Lead TO-92 Plastic
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
–55°C to 125°C
–55°C to 125°C
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
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LT1431
elecTrical characTerisTics
SYMBOL
V
REF
∆V
REF
/∆T
PARAMETER
Reference Voltage
Reference Drift
The
l
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)
LT1431I, LT1431M
CONDITIONS
V
KA
= 5V, I
K
= 2mA, (Note 3)
l
LT1431C
MIN
TYP
MAX
UNITS
V
V
ppm/°C
0.5
1.0
1.2
1.0
1
2
1
2
0.2
100
260
mV/V
µA
µA
mA
µA
µA
µA
µA
Ω
mA
V
MIN
TYP
MAX
2.490 2.500 2.510 2.490 2.500 2.510
2.465
2.535 2.480
2.520
50
0.2
0.2
0.5
1.0
1.5
1.0
1
15
1
5
0.2
80
360
30
0.2
0.2
0.6
V
KA
= 5V, I
K
= 2mA
I
K
= 2mA, V
KA
= 3V to 36V
V
KA
= 5V, T
A
= 25°C
l
l
∆V
REF
/∆V
KA
Voltage Ratio, Reference to
Cathode (Open-Loop Gain)
|I
REF
|
I
MIN
|I
OFF
|
|I
LEAK
|
|Z
KA
|
I
LIM
Reference Input Current
Minimum Operating Current
Off-State Cathode Current
l
V
KA
= V
REF
to 36V
V
KA
= 36V, V
REF
= 0V
l
0.6
Off-State Collector Leakage Current V
COLL
= 36V, V
+
= 5V, V
REF
= 2.4V
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Dynamic Impedance
Collector Current Limit
5V Reference Output
V
KA
= V
REF
, I
K
= 1mA to 100mA, f ≤ 1kHz
V
KA
= V
REF
+ 50mV
Internal Divider Used, I
K
= 2mA
l
4.950 5.000 5.050 4.950 5.000 5.050
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
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
.
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LT1431
Typical perForMance characTerisTics
1000
900
800
700
I
K
(µA)
600
500
I
MIN
V
REF
(V)
2.5V Reference I
K
vs V
KA
2.505
2.504
2.503
2.502
2.501
2.500
2.499
2.498
2.497
2.496
V
REF
and I
REF
vs V
+
3.5
3.0
2.5
2.0
2.505
2.504
2.503
2.502
V
REF
(V)
2.501
2.500
2.499
2.498
2.497
2.496
2.495
I
REF
(µA)
V
REF
and I
REF
vs V
+
3.5
3.0
2.5
2.0
1.5
I
REF
(µA)
V
REF
I
REF
1.5
1.0
0.5
0
400
300
V
REF
1.0
0.5
0
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
–0.5
–1.0
I
REF
–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
0
4
8
12 16 20 24 28 32 36 40
V
+
(V)
LT1431 TPC03
–1.5
2.5025
2.5000
2.4975
V
REF
(V)
2.4950
2.4925
2.4900
V
REF
and I
REF
vs Temperature
V
REF
I
LIMIT
vs Temperature with
External Resistor
1.00
0.66
I
LIMIT
(NORMALIZED)
0.33
I
REF
(µA)
1.250
1.125
1.000
0.875
0.750
0.625
0.500
–50 –25
V
SAT
(V)
0.7
I
LIMIT
=
AT 25°C
R
LIM
+ 3.6
1.20
1.00
0.80
0.60
COLLECTOR V
SAT
vs
Temperature vs Current
I
COLL
= 100mA
I
REF
0
I
COLL
= 50mA
0.40
0.20
0
–50 –25
I
COLL
= 20mA
I
COLL
= 10mA
50
25
75
0
TEMPERATURE (°C)
100
125
–0.33
–0.66
–1.00
125
2.4875
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
LT1431 TPC04
50
25
75
0
TEMPERATURE (°C)
100
125
LT1431 TPC05
LT1431 TPC06
Propagation Delay vs Overdrive
150
135
PROPAGATION DELAY (µs)
120
105
90
75
60
45
30
15
0
0
50
OUTPUT HIGH-TO-LOW
OUTPUT LOW-TO-HIGH
150
100
OVERDRIVE (mV)
200
250
V
REF
± OVERDRIVE
5V 1k
3
LT1431
5
6
1
OUTPUT
Voltage Gain and Phase
vs Frequency
140
120
REF-TO-COLL 1k LOAD A
V
(dB)
100
80
60
40
20
0
–20
100
1k
10k
100k
FREQUENCY (Hz)
1M
A
V
PHASE
180
135
10
10
10
9
REF-TO-COLL g
m
(µ )
10
8
10
7
10
6
10
5
10
4
10
3
Transconductance and Phase
vs Frequency (REF to COLL)
180
135
PHASE
90
45
0
–45
–90
–135
1k
10k
100k
FREQUENCY (Hz)
1M
–180
10M
PHASE (DEG)
90
45
0
–45
–90
–135
–180
10M
PHASE (DEG)
g
m
10
2
100
LT1431 TPC07
LT1431 TPC08
LT1431 TPC09
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LT1431
Typical perForMance characTerisTics
10
4
Transconductance and Phase
vs Frequency (Ref to Comp)
PHASE
g
m
20
0
–20
Z
KA
( )
–40
PHASE (DEG)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Dynamic Impedance vs Frequency
I
K
≤ 100mA
3.0
2.5
2.0
V
COMP
(V)
1.5
1.0
0.5
V
COMP
vs Temperature vs I
COLL
REF-TO-COLL g
m
(µ )
3
×
10
3
I
COLL
= 100mA
I
COLL
= 10mA
10
3
–60
–80
3
×
10
2
–100
–120
0.1
100
1k
10k
100k
FREQUENCY (Hz)
1M
–140
10M
0
100
LT1431 TPC10
1k
10k
FREQUENCY (Hz)
100k
LT1431 TPC11
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
LT1431 TPC12
I
COMP
vs V
COMP
vs V
REF
600
500
NOISE (nV/√Hz)
400
I
COMP
(µA)
300
200
V
REF
= 2.53V
100
0
0
V
REF
= 5V
V
REF
= 4V
V
REF
= 3V
1000
Noise vs Frequency
0.1Hz to 10Hz Noise
500
0
0.5
1.0
1.5 2.0
V
COMP
(V)
2.5
3.0
3.5
NOISE VOLTAGE (50µV/DIV)
1
10
100
1k
FREQUENCY (Hz)
10k
100k
LT1431 G14
0
1
LT1431 TPC13
4
3
2
TIME (MINUTES)
5
6
LT1431 TPC15
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