Datasheet

5
LT1616
BLOCK DIAGRA
W
3
Σ
R
DRIVER
Q1
S
OSC
SLOPE
COMP
FREQUENCY
FOLDBACK
INT REG
AND
UVLO
V
C
g
m
1.25V
FB
1616BD
2
GND
5
V
IN
4
SHDN
Q
Q
1
BOOST
6
SW
OPERATIO
U
The LT1616 is a constant frequency, current mode Buck
regulator. The 1.4MHz oscillator enables an RS flip-flop,
turning on the internal 600mA power switch Q1. An ampli-
fier and comparator monitor the current flowing between
the V
IN
and SW pins, turning the switch off when this current
reaches a level determined by the voltage at V
C
. An error
amplifier measures the output voltage through an external
resistor divider tied to the FB pin. This amplifier servos the
switch current to regulate the FB pin voltage to 1.25V. An
active clamp on the V
C
node provides current limit.
An internal regulator provides power to the control cir-
cuitry. This regulator includes an undervoltage lockout to
prevent switching when V
IN
is less than ~3.5V. The
(Refer to Block Diagram)
SHDN pin is used to place the LT1616 in shutdown,
disconnecting the output and reducing the input current
to less than 1µA.
The switch driver operates from either the input or from
the BOOST pin. An external capacitor and diode are used
to generate a voltage at the BOOST pin that is higher than
the input supply. This allows the driver to fully saturate the
internal bipolar NPN power switch for efficient operation.
The oscillator reduces the LT1616’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the output current during start-
up and overload.
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