LTC7813 datasheet(11/48 Pages) AD

11 / 48 page

LTC7872

Rev. 0

For more information www.analog.com

CLKOUT (Pin 38): Clock Output Pin. Use this pin to syn-

chronize multiple LTC7872 ICs. Signal swing is from V5

to ground.

MODE (Pin 39): Mode Set Pin. Tying this pin to SGND

enables forced continuous mode in buck or boost modes.

Floating this pin results in burst mode in buck mode and

discontinuous mode in boost mode. Tying this pin to V5

enables discontinuous mode in buck or boost modes. The

input impedance of this pin is 90kΩ.

SYNC (Pin 40): Switching Frequency Synchronization

or Spread Spectrum Set Pin. Applying an external clock

between 60kHz to 750kHz to this pin causes the switch-

ing frequency to synchronize to the clock signal. If SYNC

is low, a resistor from the FREQ pin to SGND sets the

switching frequency. Tying this pin to V5 allows switching

frequency spread spectrum. This pin has a 100kΩ internal

resistor to ground.

FREQ (Pin 41): Frequency Set Pin. A resistor between

this pin and SGND sets the switching frequency. This pin

sources 20µA current.

BUCK (Pin 42): The voltage on this pin determines if the

IC is regulating the VLOW or VHIGH voltage/current. Float

or tie this pin to V5 for buck mode operation. Ground this

pin for boost mode operation.

CSB, SDO, SDI, SCLK (Pins 27, 28, 29, 30): 4-Wire Serial

Peripheral Interface (SPI). Active low chip select (CSB),

serial clock (SCLK) and serial data in (SDI) are digital

Inputs. Serial data out (SDO) is an open-drain NMOS out-

put pin. SDO requires an external pull-up resistor. Refer

to the Serial Port section for more details.

EXTVCC (Pin 31): External Power Input to an Internal LDO

Connected to DRVCC. This LDO supplies DRVCC power,

bypassing the internal LDO powered from VHIGH, when-

ever EXTVCC is higher than its switchover threshold. Do

not exceed 60V on this pin.

DRVSET (Pin 32): The voltage setting on this pin pro-

grams the DRVCC output voltage. There are two internal

resistors, 200kΩ and 160kΩ, connecting this pin to the

V5 and SGND, respectively.

DRVCC (Pin 34): Gate Driver Current Supply LDO Output.

The voltage on this pin can be set to 5V, 8V, or 10V by

the DRVSET pin. Bypass this pin to ground plane with a

minimum of 4.7μF low ESR tantalum or ceramic capacitor.

NC (Pin 35): No Connect Pin.

VHIGH (Pin 36): Main VHIGH Supply. Bypass this pin to

ground with a capacitor (0.1μF to 1μF).

ILIM (Pin 37): Current Comparator Sense Voltage Limit

Selection Pin. The input impedance of this pin is 100kΩ.

PIN FUNCTIONS

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