LT1185C Linear Technology, LT1185C Datasheet

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LT1185C

Manufacturer Part Number
LT1185C
Description
Low Dropout Regulator
Manufacturer
Linear Technology
Datasheet

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The LT
current limit and remote sense capability. It can be used as
a positive output regulator with floating input or as a
standard negative regulator with grounded input. The
output voltage range is 2.5V to 25V, with 1% accuracy on
the internal reference voltage.
TYPICAL
6V TO 16V
FEATURE
D
+
V
ESCRIPTIO
Low Resistance Pass Transistor: 0.25
Dropout Voltage: 0.75V at 3A
Accurate Programmable Current Limit
Shutdown Capability
Internal Reference Available
Standard 5-Lead Packages
Full Remote Sense
Low Quiescent Current: 2.5mA
Good High Frequency Ripple Rejection
IN
1% Reference Voltage
*CURRENT LIMIT = 15k/R
®
1185 is a 3A low dropout regulator with adjustable
+
5V, 3A Regulator with 3.5A Current Limit
C2
2 F
TANT
A
S
V
PPLICATI
IN
REF
U
R
4.3k
LIM
LIM
LT1185
*
= 3.5A
GND
O
V
OUT
FB
U
R1
2.37k
R2
2.67k
+
C1
2 F
TANT
LT1185 • TA01
5V AT 3A
V
OUT
+
The LT1185 uses a saturation-limited NPN transistor as
the pass element. This device gives the linear dropout
characteristics of an FET pass element with significantly
less die area. High efficiency is maintained by using special
anti-saturation circuitry that adjusts base drive to track
load current. The “on resistance” is typically 0.25 .
Accurate current limit is programmed with a single 1/8W
external resistor, with a range of zero to three amperes. A
second, fixed internal limit circuit prevents destructive
currents if the programming current is accidentally over-
ranged. Shutdown of the regulator output is guaranteed
when the program current is less than 1 A, allowing
external logic control of output voltage.
The LT1185 has all the protection features of previous LTC
regulators, including power limiting and thermal shut-
down. The 4-lead TO-3 package is specified for –55 C to
150 C operation and the 5-lead TO-220 is specified over
0 C to 125 C.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Low Dropout Regulator
1.6
1.2
1.0
0.6
1.4
0.8
0.4
0.2
0
0
T
1
Dropout Voltage
J
LOAD CURRENT (A)
= 125 C
T
T
J
J
2
= 25 C
= –55 C
3
LT1185 • TA02
4
LT1185
1

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LT1185C Summary of contents

Page 1

... The LT1185 has all the protection features of previous LTC regulators, including power limiting and thermal shut- down. The 4-lead TO-3 package is specified for – 150 C operation and the 5-lead TO-220 is specified over 125 C. , LTC and LT are registered trademarks of Linear Technology Corporation. + 1.6 R1 1.4 2 ...

Page 2

... Control Section LT1185C ............................................. 125 C LT1185I .......................................... – 125 C LT1185M ........................................ – 150 C Power Transistor Section LT1185C ............................................. 150 C LT1185I .......................................... – 150 C LT1185M ........................................ – 175 C Storage Temperature Range ................ – 150 C Lead Temperature (Soldering, 10 sec)................ 300 C *See Application Section for details on calculating Operation Junction Temperature ...

Page 3

... LIM 0. 0.05 LIM LIM 2 0.005 0.014 0.003 0. for the LT1185C, – for LT1185I, and –55 C for JMAX is the maximum specified dropout voltage; . OUT . LIM – 1.5V 5V 3.5V OUT IN OUT OUT UNITS A• mA/A mA/A ...

Page 4

LT1185 W U TYPICAL PERFOR A Internal Current Limit 5 4 GUARANTEED LIMIT 3 TYPICAL 2 GUARANTEED 1 LIMIT TEST POINTS INPUT-OUTPUT DIFFERENTIAL (V) LT1185 • TPC01 Ground Pin Current 160 T ...

Page 5

U U APPLICATIO S I FOR ATIO Block Diagram A simplified block diagram of the LT1185 is shown in Figure 1. A 2.37V bandgap reference is used to bias the input of the error amplifier A1, and the reference amplifier ...

Page 6

LT1185 U U APPLICATIO S I FOR ATIO Amplifier A2 is used to generate an internal current through Q4 when an external resistor is connected from the REF pin to ground. This current is equal to 2.37V divided by R ...

Page 7

U U APPLICATIO S I FOR ATIO Large output capacitors (electrolytic or solid tantalum) will not cause the LT1185 to oscillate, but they will cause a damped “ringing” at light load currents where the ESR of the capacitor is several ...

Page 8

LT1185 U U APPLICATIO S I FOR ATIO factor is that local ambient temperature may be somewhat higher because of the point source of heat. The conse- quences of excess junction temperature include poor reliability, especially for plastic packages, and ...

Page 9

U U APPLICATIO S I FOR ATIO + V IN – *R1 SHOULD BE CONNECTED DIRECTLY TO GROUND LEAD, NOT TO THE LOAD, SO THAT r ERRORS CREATED BY r INCREASES WITH INCREASING GROUND PIN CURRENT. R2 SHOULD BE CONNECTED ...

Page 10

LT1185 U U APPLICATIO S I FOR ATIO + 2.4k – Logic, Positive Regulated Output † LIM 4k REF GND + FB LT1185 R2 V OUT *CMOS LOGIC ...

Page 11

U U APPLICATIO S I FOR ATIO Thermal Regulation IC regulators have a regulation term not found in discrete designs because the power transistor is thermally coupled to the reference. This creates a shift in the output voltage which is ...

Page 12

LT1185 TYPICAL APPLICATIO 15k + 2 F 2N3906 V IN TANT GND REF – V LT1185 IN V OUT LT1185 • TA03a Auxiliary + 12V Low Dropout Regulator for Switching Supply PRIMARY *DIODE CONNECTION INDICATES A FLYBACK ...

Page 13

TYPICAL APPLICATIO S Low Input Voltage Monitor Tracks Dropout Characteristics + + 2.2 F 360k TANT V IN REF R4** 1k R5* 0.01 – R6** 1k OPTIONAL HYSTERSIS 3 + LT1006 2 – Time Delayed ...

Page 14

LT1185 W SCHE ATIC DIAGRA 14 W ...

Page 15

... Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of circuits as described herein will not infringe on existing patent rights. U Dimensions in inches (millimeters) unless otherwise noted. ...

Page 16

... A Supply Current, 2.5V Reference Output 400mV Dropout Voltage Supply Current 45 A Supply Current, Adjustable Current Limit For High Performance Microprocessors 1N4001 ADD FOR INDUCTIVE LOADS + C1 4 OUT TANT C3 0.05 F – = 5V, OUT 1185fd LT/GP 0499 2K REV D • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1994 ...

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