6
LTC3251/
LTC3251-1.2/LTC3251-1.5
32511215fb
UU
U
PI FU CTIO S
MD0 (Pin 1)/MD1 (Pin 9): Switching Mode Input Pins. The
Mode input pins are used to set the operating mode of the
LTC3251. The modes of operation are:
MD1 MD0 OPERATING MODE
0 0 Shutdown
0 1 Spread Spectrum with Burst
1 0 Continuous Spread Spectrum
1 1 Super Burst
MD0 and MD1 are high impedance CMOS inputs and must
not be allowed to float.
V
IN
(Pin 2): Input Supply Voltage. Operating V
IN
may be
between 2.7V and 5.5V. Bypass V
IN
with a ≥1µF low ESR
ceramic capacitor to GND (C
OUT
).
C1
+
(Pin 3): Flying Capacitor 1 Positive Terminal (C1).
C1
–
(Pin 4): Flying Capacitor 1 Negative Terminal (C1).
GND (Pin 5, 11): Ground. Connect to a ground plane for
best performance.
C2
–
(Pin 6): Flying Capacitor 2 Negative Terminal (C2).
V
OUT
(Pin 7): Regulated Output Voltage. V
OUT
is discon-
nected from V
IN
during shutdown. Bypass V
OUT
with a
low ESR ceramic capacitor to GND (C
IN
). See V
OUT
Capacitor Selection for capacitor size requirements.
C2
+
(Pin 8): Flying Capacitor 2 Positive Terminal (C2).
FB (Pin 10) (LTC3251): Feedback Input Pin. An output
divider should be connected from V
OUT
to FB to program
the output voltage.
MODE (Pin 10) (LTC3251-1.2/LTC3251-1.5): Spread
Spectrum Operation Mode Pin. A low voltage on MODE
enables spread spectrum operation. When MODE is high
spread spectrum operation is disabled and switching
occurs at the maximum operating frequency.
