LTC3858_15 Datasheet, PDF (8/38 Pages) Linear Technology – Low IQ, Dual 2-Phase Synchronous Step-Down Controller

LTC3858
TYPICAL PERFORMANCE CHARACTERISTICS
INTV_CC and EXTV_CC
vs Load Current
5.20
V_IN = 12V
5.15
5.10
EXTVCC = 0V
5.05
EXTVCC = 8V
5.00
4.95
0 20 40 60 80 100 120 140 160 180 200
LOAD CURRENT (mA)
3858 G26
Latch-Off Threshold Voltages
vs Temperature
2.3
2.2
2.1
ARMING THRESHOLD
2.0
1.9
1.8
1.7
1.6
LATCH-OFF THRESHOLD
1.5
1.4
1.3
1.2
–45 –20
5 30 55 80 105 130
TEMPERATURE (°C)
3858 G27
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
Voltage-Controlled Oscillator (VCO). Connecting this pin
to GND forces the VCO to a fixed low frequency of 350kHz.
Connecting this pin to INTV_CC forces the VCO to a fixed
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 LTC3858 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 floated. 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.
3858fc
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