Datasheet

LTC3858-1
8
38581fd
PIN FUNCTIONS
(QFN/SSOP)
SENSE1
–
, SENSE2
–
(Pin 2, Pin 8/Pin 4, 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 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
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 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 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 7/Pin 8, 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
fl oat these pins.
INTV
CC
vs Load Current
Latchoff Threshold Voltage
vs Temperature
TYPICAL PERFORMANCE CHARACTERISTICS
LOAD CURRENT (mA)
0
INTV
CC
VOLTAGE (V)
5.10
5.15
5.20
160
3858 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
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
3858 G27
1.4
2.0
2.1
1.8
–20
30
105
130
ARMING THRESHOLD
LATCHOFF THRESHOLD