LTC3858-1 Datasheet, PDF (8/38 Pages) Linear Technology – Low IQ, Dual 2-Phase Synchronous Step-Down Controller

LTC3858-1
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)
3858 G26
Latch-Off Threshold Voltage
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 (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 Voltage-Contolled 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
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
LTC3858-1 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 1.2V shuts down that controller. Forcing both of
these pins below 0.7V shuts down the entire LTC3858‑1,
reducing quiescent current to approximately 8µA. Do NOT
float these pins.
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