LTC3788-1 Datasheet, PDF (9/28 Pages) Linear Technology – 2-Phase, Dual Output Synchronous Boost Controller

LTC3788-1
PIN FUNCTIONS
ITH1, ITH2 (Pin 1, Pin 13): Current Control Threshold
and Error Amplifier Compensation Point. The voltage on
this pin sets the current trip threshold.
VFB1, VFB2 (Pin 2, Pin 12): Error Amplifier Feedback
Input. This pin receives the remotely sensed feedback
voltage from an external resistive divider connected across
the output.
SENSE1⁺, SENSE2⁺ (Pin 3, Pin 11): Positive Current
Sense Comparator Input. The (+) input to the current
comparator is normally connected to the positive terminal
of a current sense resistor. 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.
SENSE1^–, SENSE2^– (Pin 4, Pin 10): Negative Current
Sense Comparator Input. The (–) input to the current
comparator is normally connected to the negative terminal
of a current sense resistor connected in series with the
inductor.The common mode voltage range on these pins
is 2.5V to 38V (40V abs max).
FREQ (Pin 5): The frequency control pin for the internal
VCO. Connecting the pin to GND forces the VCO to a fixed
low frequency of 350kHz. Connecting the pin to INTV_CC
forces the VCO to a fixed high frequency of 535kHz. The
frequency can be programmed from 50kHz to 900kHz
by connecting a resistor from the FREQ pin to GND. The
resistor and an internal 20μA source current create a volt-
age used by the internal oscillator to set the frequency.
Alternatively, this pin can be driven with a DC voltage to
vary the frequency of the internal oscillator.
PLLIN/MODE (Pin 6): Forced Continuous Mode, Burst
Mode or Pulse-Skipping Mode Selection Pin and External
Synchronization Input to Phase Detector Pin. Pulling this
pin to ground selects Burst Mode operation. 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. A clock
on the pin will force the controller into pulse-skipping
mode of operation and synchronize the internal oscillator.
SGND (Pin 7): Signal Ground. All small-signal components
and compensation components should connect to this
ground, which in turn connects to PGND at a single point.
RUN1, RUN2 (Pin 8, Pin 9): Run Control Input. An external
resistor divider connects to V_IN and sets the thresholds for
converter operation with a threshold of 1.28V. Once running,
a 4.5μA current is sourced from the RUN pin allowing the
user to program hysteresis using the resistor values.
INTV_CC (Pin 19): Output of Internal 5.4V LDO. Power
supply for control circuits and gate drives. Decouple this
pin to GND with a minimum 4.7μF low ESR tantalum or
ceramic capacitor.
EXTV_CC (Pin 20): External Power Input. When this pin is
higher than 4.8V an internal switch bypasses the inter-
nal regulator and supply power to INTV_CC directly from
EXTV_CC.
PGND (Pin 21): Driver Power Ground. Connects to the
sources of bottom (main) N-channel MOSFETs and the
(–) terminal(s) of C_IN and C_OUT.
VBIAS (Pin 22): Main Supply Pin. It is normally tied to the
input supply V_IN or to the output of the boost converter. A
bypass capacitor should be tied between this pin and the
signal ground pin.The operating voltage range on this pin
is 4.5V to 38V (40V abs max).
BG1, BG2 (Pin 23, Pin 18): Bottom Gate. Connect to the
gate of the main NMOS.
BOOST1, BOOST2 (Pin 24, Pin 17): Floating power supply
for the synchronous NMOS. Bypass to SW with a capacitor
and supply with a Schottky diode connected to INTV_CC.
TG1, TG2 (Pin 25, Pin 16): Top Gate. Connect to the gate
of the synchronous NMOS.
SW1, SW2 (Pin 26, Pin 15): Switch Node. Connect to the
source of the synchronous NMOS, the drain of the main
NMOS and the inductor.
PGOOD1 (Pin 27): Power Good Indicator for Channel 1.
Open-drain logic output that is pulled to ground when
the output voltage is more than ±10% away from the
regulated output voltage. To avoid false trips the output
voltage must be outside the range for 25μs before this
output is activated.
SS1, SS2 (Pin 28, Pin 14): Output Soft-Start Input. A
capacitor to ground at this pin sets the ramp rate of the
output voltage during start-up.
37881f
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