Datasheet

LTC3786
8
3786fc
For more information www.linear.com/LTC3786
TYPICAL PERFORMANCE CHARACTERISTICS
Charge Pump Charging Current
vs Operating Frequency
Charge Pump Charging Current
vs Switch Voltage
PIN FUNCTIONS
(MSOP/QFN)
VFB (Pin 1/Pin 3): Error Amplifier Feedback Input. This
pin receives the remotely sensed feedback voltage from
an external resistive divider connected across the output.
SENSE
+
(Pin 2/Pin 4): Positive Current Sense Comparator
Input. The (+) input to the current comparator is normally
connected to the positive terminal of a current sense resis
-
tor. The current sense resistor is normally placed at the
input of the boost controller in series with the inductor.
This pin also supplies power to the current comparator.
SENSE
–
(Pin 3/Pin 5): Negative Current Sense Comparator
Input. The (–) input to the current comparator is normally
connected to the negative terminal of a current sense re
-
sistor connected in series with the inductor. The common
mode voltage range on the SENSE
+
and SENSE
–
pins is
2.5V to 38V (40V abs max).
ITH (Pin 4/Pin 6): Current Control Threshold and Error
Amplifier Compensation Point. The voltage on this pin
sets the current trip threshold.
SS (Pin 5/Pin 7): Output Soft-Start Input. A capacitor to
ground at this pin sets the ramp rate of the output voltage
during start-up.
PLLIN/MODE (Pin 6/Pin 8): External Synchronization Input
to Phase Detector and Forced Continuous Mode Input.
When an external clock is applied to this pin, it will force
the controller into forced continuous mode of operation
and the phase-locked loop will force the rising BG signal
to be synchronized with the rising edge of the external
clock. When not synchronizing to an external clock, this
input determines how the LTC3786 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. This can
be done by adding a 100k resistor between the PLLIN/
MODE pin and INTV
CC
.
–45°C
V
SW
= 12V
25°C
130°C
155°C
V
BOOST
= 16.5V
OPERATING FREQUENCY (kHz)
50
150
250
350
450
550
650
750
850
0
10
20
30
40
50
60
70
80
90
100
110
CHARGE PUMP CHARGING CURRENT (µA)
3786 G27
SWITCH VOLTAGE (V)
5
CHARGE PUMP CHARGING CURRENT (µA)
80
100
120
20 30
3786 G28
60
40
10 15
25 35 40
20
0
FREQ = 0V
FREQ = INTV
CC
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