Datasheet

LTC1871-1
7
18711fb
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.
I NTV
CC
(Pin 8): The Internal 5.20V 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.
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 the drain of the power MOSFET
for V
DS
sensing and highest effi ciency. Alternatively, the
SENSE pin may be connected to a resistor in the source
of the power MOSFET. 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
0.175V
1.230V
5.2V
–
+
2.00V
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
18711 BD
6
GATE
INTV
CC
GND
7
V
IN
1.248V
9
RUN
C2
1
0.6V