Datasheet LTC3785-1 (Analog Devices) - 6

LTC3785-1
PIN FUNCTIONS VSENSE (Pin 4):
Overvoltage and Undervoltage Sense.
ISSW2 (Pin 14):
Reverse Current Limit Comparator Invert- The overvoltage threshold is internally set 7.5% above ing Input. This pin is normally connected to the source of the regulated FB voltage and the undervoltage threshold the N-channel MOSFET D (TG2 driven). is internally set 7.5% below the FB regulated voltage. This
V
pin can be tied to FB but to optimize the response time it
DRV (Pin 16):
Driver Supply for Ground Referenced Switches. Connect this pin to V is recommended that a separate voltage divider from V CC potential. OUT be applied. The divider can be skewed from the feedback
BG1, BG2 (Pins 17, 15):
Bottom gate driver pins drive value to achieve the desired UV or OV threshold. the ground referenced N-channel MOSFET switches B and C.
ILSET (Pin 5):
Current Limit Set. A resistor from this pin to ground sets the current limit threshold from the I
I
SVIN
SSW1 (Pin 18):
Forward Current Limit Comparator Non- and I inverting Input. This pin is normally connected to the SSW1 pins. source of the N-channel MOSFET A (TG1 driven).
CCM (Pin 6):
Continuous Conduction Mode Control Pin. When set low, the inductor current is allowed to go slightly
SW1 (Pin 19):
Ground Reference for Driver A. Gate drive negative (–15mV referenced to the I from TG1 will reference to the common point of output SVOUT – ISSW2 pins). When driven high, the reverse current limit is set to the similar switches A and B. value of the forward current limit set by the ILSET pin.
TG1, TG2 (Pins 20, 12):
Top gate drive pins drive the
RT (Pin 7):
Oscillator Programming Pin. A resistor from top N-channel MOSFET switches A and D with a voltage this pin to GND sets the free-running frequency of the IC. swing equal to VCC – VDIODE superimposed on the SW1 f and SW2 nodes respectively. OSC ≅ 2.5e10/RT.
MODE (Pin 8):
Burst Mode Control Pin.
VBST1 (Pin 21):
Boosted Floating Driver Supply for the Buck Switch A. This pin will swing from a diode below • MODE = High: Enable Burst Mode Operation. In Burst V Mode operation the operation is variable frequency, CC up to VIN + VCC – VDIODE. which provides a signifi cant effi ciency improvement
ISVIN (Pin 22):
Forward Current Limit Comparator Invert- at light loads. The Burst Mode operation will continue ing Input. This pin is normally connected to the drain of until the pin is driven low. N-channel MOSFET A (TG1 driven). • MODE = Low: Disable Burst Mode operation and maintain
VCC (Pin 23):
Internal 4.35V LDO Regulator Output. The low noise, constant frequency operation. driver and control circuits are powered from this voltage to limit the maximum VGS drive voltage. Decouple this pin
PGOOD (Pin 9):
Open Drain Output. PGOOD is pulled to to power ground with at least a 4.7μF ceramic capacitor. ground when the voltage on VSENSE is not within ±7.5% For low V of its setpoint. PGOOD will also be pulled low when the IN applications, VCC can be bootstrapped from V part is in shutdown or input UVLO. OUT through a Schottky diode.
V I IN (Pin 24):
Input Supply Pin for the VCC Regulator. A
SVOUT (Pin 10):
Reverse Current Limit Comparator Non- ceramic capacitor of at least 10μF is recommended close inverting Input. This pin is normally connected to the drain to the V of the N-channel MOSFET D (TG2 driven). IN and GND pins.
Exposed Pad (Pin 25):
The GND and PGND pins are con-
VBST2 (Pin 11):
Boosted Floating Driver Supply for Boost nected to the Exposed Pad which must be connected to Switch D. This pin will swing from a diode below VCC up the PCB ground for electrical contact and rated thermal to VOUT + VCC – VDIODE. performance.
SW2 (Pin 13):
Ground Reference for Driver D. Gate drive from TG2 will reference to the common point of output switches C and D. 37851fa 6