Datasheet

LTC3868
8
3868fd
PIN FUNCTIONS
SENSE1
–
, SENSE2
–
(Pin 1, Pin 9): The (–) Input to the
Differential Current Comparators. When greater than
INTV
CC
– 0.5V, the SENSE
–
pin supplies current to the
current comparator.
FREQ (Pin 2): The Frequency Control Pin for the Internal
VCO. Connecting this pin to GND forces the VCO to a fi xed
low frequency of 350kHz. Connecting this pin to INTV
CC
forces the VCO to a fi xed high frequency of 535kHz.
Other frequencies between 50kHz and 900kHz can be
programmed using a resistor between FREQ and GND.
An internal 20µA pull-up current develops the voltage to
be used by the VCO to control the frequency
PHASMD (Pin 3): Control input to phase selector which
determines the phase relationships between controller 1,
controller 2 and the CLKOUT signal. Pulling this pin to
ground forces TG2 and CLKOUT to be out of phase 180°
and 60° with respect to TG1. Connecting this pin to INTV
CC
forces TG2 and CLKOUT to be out of phase 240° and 120°
with respect to TG1. Floating this pin forces TG2 and
CLKOUT to be out of phase 180° and 90° with respect to
TG1. Refer to the Table 1.
CLKOUT (Pin 4): Output clock signal available to daisy-
chain other controller ICs for additional MOSFET driver
stages/phases. The output levels swing from INTV
CC
to
ground.
PLLIN/MODE (Pin 5): External Synchronization Input to
Phase Detector and Forced Continuous Mode Input. When
an external clock is applied to this pin, the phase-locked
loop will force the rising TG1 signal to be synchronized
with the rising edge of the external clock. When not syn-
chronizing to an external clock, this input, which acts on
both controllers, determines how the LTC3868 operates at
light loads. Pulling this pin to ground selects Burst Mode
operation. An internal 100k resistor to ground also invokes
Burst Mode operation when the pin is fl oated. Tying this pin
to INTV
CC
forces continuous inductor current operation.
Tying this pin to a voltage greater than 1.2V and less than
INTV
CC
– 1.3V selects pulse-skipping operation.
SGND (Pin 6, Exposed Pad Pin 33): Small-signal ground
common to both controllers, must be routed separately
from high current grounds to the common (–) terminals
of the C
IN
capacitors. The exposed pad must be soldered
to the PCB for rated thermal performance.
INTV
CC
and EXTV
CC
vs Load Current
Latchoff Thresholds
vs Temperature
LOAD CURRENT (mA)
0
INTV
CC
VOLTAGE (V)
5.10
5.15
5.20
160
3868 G26
5.05
5.00
4.95
20 40 60
80 100
120 140 180
200
EXTV
CC
= 0V
V
IN
= 12V
EXTV
CC
= 8V
TYPICAL PERFORMANCE CHARACTERISTICS
TEMPERATURE (°C)
–45
1.2
INTV
CC
VOLTAGE (V)
1.3
1.5
1.6
1.7
2.3
2.2
1.9
5
55
80
3868 G27
1.4
2.0
2.1
1.8
–20
30
105
130
ARMING THRESHOLD
LATCH-OFF THRESHOLD