LT1431C Linear Technology, LT1431C Datasheet - Page 6

• Manufacturer Part Number: LT1431C
• Description: Programmable Reference
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
TYPICAL APPLICATIO S
LT1431
Frequency Compensation
As a shunt regulator, the LT1431 is stable for all capacitive
loads on the COLL pin. Capacitive loading between 0.01 F
and 18 F causes reduced phase margin with some ringing
under transient conditions. Output capacitors should not
be used arbitrarily because output noise is not necessarily
reduced.
Excess capacitance on the REF pin can introduce enough
phase shift to induce oscillation when configured as a
reference >2.5V. This can be compensated with capaci-
tance between COLL and REF (phase lead). More compli-
cated feedback loops may require shaping of the fre-
quency response of the LT1431 with dominant pole or
6
V
IN
LT1431Z
2.5V Reference
3-Pin Package
R
R
= R (0.5mA) ±25% PROCESS TOLERANCE
L
CATHODE
V
R
500mV
Increasing 5V Reference
ANODE
GND-S
IN
TOP
V
U U
+
REF
LT1431
R
LT1431 • TA02
L
GND-F
COLL
R
2.5V
REF
MID
LT1431 • TA05
U
W
5V +
V
GND-S
IN
V
U
+
LT1431
2.5V Reference
8-Pin Package
R
L
GND-F
COLL
REF
pole-zero compensation. This can be accomplished with a
capacitor or series resistor and capacitor between COLL
and COMP.
The compensation schemes mentioned above use voltage
feedback to stabilize the circuits. There must be voltage
gain at the COLL pin for them to be effective, so the COLL
pin must see a reasonable AC impedance. Capacitive
loading of the COLL pin reduces the AC impedance,
voltage gain, and frequency response, thereby decreasing
the effectiveness of the compensation schemes, but also
decreasing their necessity.
LT1431 • TA03
2.5V
V
GND-S
IN
Programmable Reference with Adjustable
V
+
LT1431
R
LIM
R
L
GND-F
COLL
Current Limit
REF
V
R
IN
GND-S
TOP
I
V
LIMIT
+
5V Reference
LT1431
R1
R2
=
R
R
LIM
L
0.7
V
+ 3.6
GND-F
OUT
COLL
R
= 1 + R1
REF
MID
AT 25°C
LT1431 • TA06
LT1431 • TA04
R2
V
REF
5V