Datasheet

LTC3835
12
3835fd
The typical capture range of the LTC3835’s phase-locked
loop is from approximately 115kHz to 800kHz, with a
guarantee to be between 140kHz and 650kHz. In other
words, the LTC3835’s PLL is guaranteed to lock to an
external clock source whose frequency is between 140kHz
and 650kHz.
The typical input clock thresholds on the PLLIN/MODE
pin are 1.6V (rising) and 1.2V (falling).
PolyPhase Applications (CLKOUT and PHASMD Pins)
The LTC3835 features two pins (CLKOUT and PHASMD)
that allow other controller ICs to be daisy-chained with
the LTC3835 in PolyPhase applications. The clock output
signal on the CLKOUT pin can be used to synchronize
additional power stages in a multiphase power supply
solution feeding a single, high current output or multiple
separate outputs. The PHASMD pin is used to adjust the
phase of the CLKOUT signal, as summarized in Table 1.
The phases are calculated relative to the zero degrees
phase being defined as the rising edge of the top gate
driver output (TG).
The CLKOUT pin has an open-drain output device. Normally,
a 10k to 100k resistor can be connected from this pin to a
voltage supply that is less than or equal to 8.5V.
Table 1
V
PHASMD
CLKOUT PHASE
GND 90°
Floating 180°
INTV
CC
120°
Output Overvoltage Protection
An overvoltage comparator guards against transient over-
shoots as well as other more serious conditions that may
overvoltage the output. When the V
FB
pin rises to more
than 10% higher than its regulation point of 0.800V, the top
MOSFET is turned off and the bottom MOSFET is turned
on until the overvoltage condition is cleared.
Power Good (PGOOD) Pin
The PGOOD pin is connected to an open drain of an internal
N-channel MOSFET. The MOSFET turns on and pulls the
PGOOD pin low when the V
FB
pin voltage is not within
±10% of the 0.8V reference voltage. The PGOOD pin is also
pulled low when the RUN pin is low (shut down). When
the V
FB
pin voltage is within the ±10% requirement, the
MOSFET is turned off and the pin is allowed to be pulled
up by an external resistor to a source of up to 8.5V.
OPERATION
(Refer to Functional Diagram)