Datasheet

LTC1871-7
7
18717fd
pin FuncTions
MODE/SYNC (Pin 5): This input controls the operating
mode of the converter and allows for synchronizing the
operating frequency to an external clock. If the MODE/
SYNC pin is connected to ground, Burst Mode operation
is enabled. If the MODE/SYNC pin is connected to INTV
CC
,
or if an external logic-level synchronization signal is ap-
plied to this input, Burst Mode operation is disabled and
the IC operates in a continuous mode.
GND (Pin 6): Ground Pin.
GATE (Pin 7): Gate Driver Output.
INTV
CC
(Pin 8): The Internal 7V Regulator Output. The
gate driver and control circuits are powered from this
voltage. Decouple this pin locally to the IC ground with a
minimum of 4.7µF low ESR tantalum or ceramic capacitor.
This 7V regulator has an undervoltage lockout circuit with
5.6V and 4.6V rising and falling thresholds, respectively.
V
IN
(Pin 9): Main Supply Pin. Must be closely decoupled
to ground.
SENSE (Pin 10): The Current Sense Input for the Control
Loop. Connect this pin to a resistor in the source of the
power MOSFET. Alternatively, the SENSE pin may be con-
nected to the drain of the power MOSFET, in applications
where the maximum V
DS
is less than 36V. Internal leading
edge blanking is provided for both sensing methods.
block DiagraM
–
+
–
+
+
1.230V
85mV
OV
50k
EA
UV
TO
START-UP
CONTROL
BURST
COMPARATOR
S
R
Q
LOGIC
PWM LATCH
CURRENT
COMPARATOR
0.30V
1.230V
7V
–
+
5.6V UP
4.6V DOWN
1.230V
SLOPE
1.230V
I
LOOP
FB
I
TH
–
+
g
m
3
MODE/SYNC
5
FREQ
4
2
INTV
CC
8
LDO
V-TO-I
OSCV-TO-I
SLOPE
COMPENSATION
BIAS AND
START-UP
CONTROL
V
IN
BIAS V
REF
I
OSC
R
LOOP
–
+
–
+
C1
SENSE
10
GND
18717 BD
6
GATE
INTV
CC
GND
7
V
IN
1.248V
9
RUN
C2
1
0.6V