LTC3858-1 Linear Technology Corporation, LTC3858-1 Datasheet - Page 8

• Manufacturer Part Number: LTC3858-1
• Description: Dual 2-Phase Synchronous Step-Down Controller
• Manufacturer: Linear Technology Corporation

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LTC3858-1
TYPICAL PERFORMANCE CHARACTERISTICS
PIN FUNCTIONS
SENSE1
to the Differential Current Comparators. When greater
than INTV
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
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.
8
–
, SENSE2
CC
– 0.5V, the SENSE
–
5.20
5.15
5.10
5.05
5.00
4.95
(Pins 2, 4/Pins 8,10): The (–) Input
0
INTV
V
IN
20 40 60 80 100 120 140
= 12V
CC
(QFN/SSOP)
vs Load Current
LOAD CURRENT (mA)
–
pin supplies current to
EXTV CC = 8V
EXTV CC = 0V
CC
forces the VCO
160
180 200
3858 G26
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
continuous inductor current operation. Tying this pin to
a voltage greater than 0.9V and less than INTV
selects pulse-skipping operation.
SGND (Pin 5/Pin 7): Small-signal ground common to
both controllers, must be routed separately from high
current grounds to the common (–) terminals of the C
capacitors.
RUN1, RUN2 (Pins 6, 8/Pins 7, 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.
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
–45
Latch-Off Threshold Voltage
vs Temperature
–20
LATCH-OFF THRESHOLD
ARMING THRESHOLD
5
TEMPERATURE (°C)
30
55
80
105
3858 G27
130
CC
CC
– 1.3V
forces
38581f
IN