LTC3868-1 Datasheet, PDF (8/38 Pages) Linear Technology – Low IQ, Dual 2-Phase Synchronous Step-Down Controller

LTC3868-1
Typical Performance Characteristics
INTV_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)
38681 G26
Latchoff Thresholds
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)
38681 G27
Pin Functions (QFN/SSOP)
SENSE1^–, SENSE2^– (Pin 2, Pin 4/Pin 8, Pin 10): 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 3/Pin 5): The Frequency Control Pin for the
Internal 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
PLLIN/MODE (Pin 4/Pin 6): 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 synchronizing to an external clock, this input,
which acts on both controllers, determines how the
LTC3868-1 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 5, Exposed Pad Pin 29/Pin 7): 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 (QFN
only) must be soldered to the PCB for rated thermal
performance.
RUN1, RUN2 (Pin 6, Pin 8/Pin 7, Pin 9): Digital Run
Control Inputs for Each Controller. Forcing either of these
pins below 1.26V shuts down that controller. Forcing both
of these pins below 0.7V shuts down the entire LTC3868‑1,
reducing quiescent current to approximately 8µA. Do not
float these pins.
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