LTC7813 datasheet(10/36 Pages) LINER

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LTC7821

Rev A

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TEMP (Pin 12): Temperature Sensing Input. Using a PTC

resistor as the lower leg of a resistor divider, connect the

TEMP pin to the common point of the divider. The PTC

resistor is used to monitor a hot spot on the PCB. Once

it reaches the TEMP threshold of 1.22V, the LTC7821

stops switching for 100ms before retrying. Ground this

pin if not used.

VFB (Pin 13): Error Amplifier Feedback Input. This pin

receives the remotely sensed feedback voltage from an

external resistive divider across the output.

ISNS– (Pin 14): Current Sense Comparator Input. The (–)

input to the current comparator is Kelvin connected to the

output voltage of the controller.

ISNS+ (Pin 15): Current Sense Comparator Input. The (+)

input to the current comparator is normally Kelvin con-

nected to the DCR sensing networks or current sensing

resistor.

EXTVCC (Pin 16): External Power Input to an Internal LDO

Connected to INTVCC. This LDO supplies INTVCC power,

bypassing the internal LDO powered from VIN whenever

EXTVCC is higher than 6.4V. Do not float or exceed 40V

on this pin.

PGND (Pin 17): Driver Power Ground. Connect this pin

closely to the source of bottom (synchronous) N-channel

MOSFET M4, the (–) terminal of CIN and the (–) terminal

of CVCC.

BG2 (Pin 18): Gate Drive for the Bottom (synchronous)

N-Channel MOSFET. The voltage swings from slightly

below ground to INTVCC.

INTVCC (Pin 19): Internal Regulator Output. The bottom

synchronous gate driver and control circuits are powered

fromthisregulator.BypassthispintoPGNDwithaminimum

of 4.7μF low ESR tantalum or ceramic capacitor. Do not

use the INTVCC pin for any purpose other than described

in this data sheet.

SW3 (Pin 20): Switch Node Connection to Inductor and

One Terminal of Flying Capacitor. Voltage swing at this pin

is from slightly below ground to VIN/2.

TG2 (Pin 21): Floating Gate Drive for Second Lowermost

N-Channel MOSFET. The voltage swings equal to INTVCC

superimposed on the switch node voltage SW3.

BOOST1,BOOST2,BOOST3(Pin31,23,22):Bootstrapped

Supplies to Floating Drivers. Capacitors are connected

between the BOOSTx and SWx (MID) pin. Voltage swing

at the BOOST1 pin is from (VIN/2 + INTVCC) to (VIN + IN-

TVCC). Voltage at the BOOST2 pin is at (VIN/2 + INTVCC).

Voltage swing at the BOOST3 pin is from INTVCC to (VIN/2

+ INTVCC).

BG1 (Pin 24): Floating Gate Drive for Second Uppermost

N-Channel MOSFET. The voltage swings between (VIN/2

+ INTVCC) and VIN/2.

MID (Pin 25): Half Supply from VIN. Do not use this to

source current. Connect a bypass capacitor from this

node to PGND.

MIDSENSE (Pin 26): Half Supply Monitor. Provides Kelvin

sensing input for the comparator that monitors the voltage

between MIDSENSE and ground. An RC filter can be added

from MID to this pin to filter out noise.

VIN_SENSE (Pin 27): VIN Kelvin Sensing Input. Allows an

internal VIN/2 to be generated for LTC7821 control circuit

usage. For a cleaner supply, an RC filter can be added

from VIN to this pin.

VIN (Pin 28): Main Input Supply. Bypass this pin to PGND

with a capacitor.

SW1 (Pin 29): Switch Node Connection to One Terminal

of Flying Capacitor. Voltage swing at this pin is from VIN/2

voltage to VIN.

TG1(Pin30):FloatingGateDriveforUppermostN-Channel

MOSFET.ThevoltageswingsequaltoINTVCCsuperimposed

on the switch node voltage SW1.

SGND (Exposed Pad, Pin 33): Signal Ground. All Small-

signalcomponentsandcompensationcomponentsshould

connect to this ground, which in turn connects to PGND

at one point. Exposed pad must be soldered to the PCB,

providing a local ground for the control components of

the IC, and be tied to the PGND pin under the IC.

PIN FUNCTIONS

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