ltc3873 Linear Technology Corporation, ltc3873 Datasheet - Page 5

• Manufacturer Part Number: ltc3873
• Description: No Rsense Constant Frequency Current Mode Boost/flyback/sepic Dc/dc Controller
• Manufacturer: Linear Technology Corporation

FUNCTIONAL DIAGRAM
PIN FUNCTIONS
IPRG (Pin 1/Pin 4): Current Sense Limit Select Pin.
I
compensation point. Nominal voltage range for this pin
is 0.7V to 1.9V.
V
from an external resistor divider across the output.
GND (Pin 4/Pin 1): Ground Pin.
NGATE (Pin 5/Pin 8): Gate Drive for the External N-Channel
MOSFET. This pin swings from 0V to V
V
decoupled to GND (Pin 4).
TH
FB
CC
(Pin 2/Pin 3): This pin serves as the error amplifi er
(Pin 3/Pin 2): This pin receives the feedback voltage
(Pin 6/Pin 7): Supply Pin. This pin must be closely
RUN/SS
V
CC
3µA
UNDERVOLTAGE
COMPARATOR
SHUTDOWN
LOCKOUT
SHDN
SOFT-START
UV
INTERNAL
(TS8/DD8)
RAMP
REFERENCE
VOLTAGE
IN
.
1.2V
I
TH
AMPLIFIER
ERROR
V
SHUNT
REGULATOR
+
–
CC
CURRENT LIMIT
BUFFER
9.5V
I
TH
CLAMP
RUN/SS (Pin 7/Pin 6): Shutdown and External Soft-Start
Pin. In shutdown, all functions are disabled and the NGATE
pin is held low.
SW (Pin 8/Pin 5): Switch node connection to inductor and
current sense input pin through external slope compensa-
tion resistor. Normally, the external N-channel MOSFET’s
drain is connected to this pin.
Exposed Pad (NA/Pin 9): Ground. Must be soldered to PCB
for electrical contact and rated thermal performance.
–
+
1.2V
LATCH
RS
–
GND
R
LOGIC CIRCUIT
I
SWITCHING
LIM
Q
+
S
SW
COMPARATOR
CURRENT
OSCILLATOR AND
MAX DUTY CYCLE
V
COMPENSATION
IN
200kHz
SLOPE
LTC3873
NGATE
IPRG
V
FB
3873 FD
5
3873f