LT1377IS8PBF LINEAR TECH, LT1377IS8PBF Datasheet - Page 5

• Manufacturer Part Number: LT1377IS8PBF
• Manufacturer: LINEAR TECH

BLOCK DIAGRA
PI FU CTIO S
V
compensation, current limiting and soft start. It is the
output of the error amplifier and the input of the current
comparator. Loop frequency compensation can be per-
formed with an RC network connected from the V
ground.
FB (Pin 2): The feedback pin is used for positive output
voltage sensing and oscillator frequency shifting. It is the
inverting input to the error amplifier. The noninverting
input of this amplifier is internally tied to a 1.245V
reference. Load on the FB pin should not exceed 250 A
when the NFB pin is used. See Applications Information.
NFB (Pin 3): The negative feedback pin is used for negative
output voltage sensing. It is connected to the inverting
input of the negative feedback amplifier through a 100k
source resistor.
S/S (Pin 4): Shutdown and Synchronization Pin. The S/S
pin is logic level compatible. Shutdown is active low and
the shutdown threshold is typically 1.3V. For normal
operation, pull the S/S pin high, tie it to V
floating. To synchronize switching, drive the S/S pin be-
tween 600kHz and 800kHz (LT1372) or 1.2MHz to 1.6MHz
(LT1377).
C
U
(Pin 1): The compensation pin is used for frequency
U
NFB
FB
GND SENSE
1.245V
100k
REF
U
50k
S/S
W
–
–
+
+
DELAY AND RESET
SYNC
NFBA
EA
SHUTDOWN
OSC
5:1 FREQUENCY
IN
SHIFT
or leave it
C
pin to
LOW DROPOUT
V
C
2.3V REG
LOGIC
COMP
V
IN
V
part goes into undervoltage lockout when V
2.5V. Undervoltage lockout stops switching and pulls the
V
GND S (Pin 6): The ground sense pin is a “clean” ground.
The internal reference, error amplifier and negative feed-
back amplifier are referred to the ground sense pin. Con-
nect it to ground. Keep the ground path connection to the
output resistor divider and the V
free of large ground currents.
GND (Pin 7): The ground pin is the emitter connection of
the power switch and has large currents flowing through it.
It should be connected directly to a good quality ground
plane.
V
switch and has large currents flowing through it. Keep the
traces to the switching components as short as possible to
minimize radiation and voltage spikes.
IN
C
SW
pin low.
(Pin 5): Bypass input supply pin with 10 F or more. The
(Pin 8): The switch pin is the collector of the power
A
V
6
IA
+
–
DRIVER
ANTI-SAT
LT1372/LT1377
C
compensation network
GND
SW
SWITCH
0.08
LT1372 • BD
IN
drops below
5