LTC7813 datasheet(8/28 Pages) AD

8 / 28 page

LTC7878

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

BG1, BG2 (Pins 1, 8): Bottom Gate Driver Outputs. These

pins drive the gates of the bottom N-Channel MOSFETs

between PGND and DRVCC.

VIN (Pin 2): Main IC Supply. Power input to the internal

LDO connect to DRVCC. Bypass this pin to PGND with a

capacitor (0.1μF to 1μF) close to the pin.

DRVCC (Pin 3): Gate Driver Current Supply LDO Output.

The voltage on this pin is regulated to 7V from either VIN

or EXTVCC during normal operation. Bypass this pin to

PGND with a minimum of 4.7μF low ESR tantalum or

ceramic capacitor.

EXTVCC (PIN 4): External Power Input to an Internal LDO

Connected to DRVCC. When the voltage on this pin is

greater 8V and lower than the VIN pin voltage, this LDO

bypasses the internal LDO powered from VIN. Bypass

this pin to PGND with a capacitor (0.1μF to 1μF) close

to the pin.

INTVCC (PIN 5): Internal 5V Regulator Output. The control

circuits are powered from this voltage. Bypass this pin

to SGND with a minimum of 4.7µF low ESR tantalum or

ceramic capacitor.

RUN (Pin 6): Enable Control Input. A voltage above 1.22V

turns on the IC. There is a 2µA pull-up current on this pin.

Once the RUN pin rises above the 1.22V threshold, the

pull-up increases to 6µA.

PGND (PIN 7): Power Ground Pin. Connect this pin closely

to the sources of bottom N-channel MOSFETs and neg-

ative terminal of VIN, DRVCC, EXTVCC bypass capacitors.

TG2, TG1 (Pins 9, 32): Top Gate Driver Outputs. These are

the outputs of floating drivers with a voltage swing equal

to DRVCC superimposed on the switching nodes voltages.

BOOST2, BOOST1 (Pins 10, 31): Bootstrapped Supplies

to the Top Side Floating Drivers. Capacitors are connected

between the BOOST and SW pins and Schottky diodes

are tied between the BOOST and DRVCC pins. Voltage

swing at the BOOST1 pin is from DRVCC to (VIN + DRVCC).

Voltage swing at the BOOST2 pin is from DRVCC to

(VOUT + DRVCC).

SW2, SW1 (Pins 11, 30): Switch Node Connections.

Normally connect to the inductor terminals. SW1 swings

from a Schottky diode voltage drop below ground up

to VIN and SW2 swings from a Schottky diode voltage

drop below ground up to VOUT. A bootstrap capacitor

(0.1μF to 1μF) should be placed from each SW pin to the

corresponding BOOST pin as close as possible.

PGOOD (Pin 12): Power Good Inductor Output for the

Regulated Output Voltage. Open-drain logic out that is

pulled down to ground when the regulated output voltage

exceeds ±10% regulation window, after the internal 30µs

power bad mask timer expires.

SS (Pin 13): Soft-Start Input. The voltage ramp rate at

this pin sets the output voltage ramp rate of the regulated

voltage. A capacitor to ground accomplishes soft-start.

This pin has a 2.5µA pull-up current.

ITHB (Pin 14): Fast Transient Current Control Threshold.

Optional transient response improvement configure pin

based on the ITH pin voltage and operation mode. A resis-

tor from ITHB pin to ITH pin may improve the transient

response in buck mode. If no use, short ITHB pin and

ITH pin together. See Applications Information section for

details. Do not float this pin.

ITH (Pin 15): Current Control Threshold and Error

Amplifier Compensation Point. The current compara-

tor’s threshold varies with the ITH control voltage. The

Compensation network is from ITH pin to SGND.

VFB (Pin 16): Output Voltage Sensing Error Amplifier

Noninverting Input. This pin receives the remotely sensed

feedback voltage from external resistor divider across the

output voltage.

MODE/ILIM (Pin 17): FCM/Pulse-Skipping Mode and

Inductor Current Limit Program Pin. Tying this pin to

GND or INTVCC enables forced continuous mode oper-

ation, otherwise the controller works in the pulse-skip-

ping mode. Tying this pin to a voltage lower than half of

INTVCC enables the low current limit, higher than half of

INTVCC enables the high current limit. See Applications

Information section for details.

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