LTC4449 datasheet(10/48 Pages) AD

10 / 48 page

LTC7872

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

SS (Pin 1): Soft-Start Input. The voltage ramp rate at this

pin sets the voltage ramp rate of the regulated voltage. A

capacitor to ground accomplishes soft-start. This pin has

a 1µA pull-up current.

VFBLOW (Pin 2): VLOW Voltage Sensing Error Amplifier

Inverting Input.

ITHHIGH/ITHLOW (Pins 5 and 3): Current Control Threshold

and Error Amplifier Compensation Point. The current com-

parator’s threshold varies with the ITH control voltage.

SGND (Pins 4, 33, Exposed Pad): Ground. Must be

soldered to PCB ground for rated thermal performance.

Connect this pin closely to negative terminal of VHIGH,

DRVCC, V5 bypass capacitors. All small signal components

and compensation components should connect here.

VFBHIGH (Pin 6): VHIGH Voltage Sensing Error Amplifier

Noninverting Input.

V5 (Pin 7): 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.

IMON (Pin 8): Current Monitor Pin. The voltage on this pin

is directly proportional to the average inductor currents

of all 4 channels. 1.25V on this pin indicates zero average

inductor current per phase.

SETCUR (Pin 9): This pin sets the maximum average

inductor current in buck or boost mode. This pin sources

16μA current and it is programmable by the SPI interface.

OVHIGH (Pin 10): VHIGH Overvoltage Threshold Set Pin. A

resistor divider from VHIGH is needed to set this thresh-

old. When the voltage on this pin rises past the 1.2V trip

point, a 5μA current is sourced out of the pin to provide

externally adjustable hysteresis.

UVHIGH (Pin 11): VHIGH Undervoltage Threshold Set Pin.

A resistor divider from VHIGH is needed to set this thresh-

old. When the voltage on this pin falls below the 1.2V

trip point, a 5μA current is sunk in to the pin to provide

externally adjustable hysteresis.

OVLOW (Pin 12): VLOW Overvoltage Threshold Set Pin. A

resistor divider from VLOW is needed to set this thresh-

old. When the voltage on this pin rises past the 1.2V trip

point, a 5μA current is sourced out of the pin to provide

externally adjustable hysteresis.

SNSA1+/SNSA2+/SNSA3+/SNSA4+ (Pins 13, 18, 43, 48):

AC Positive Current Sense Comparator Inputs. These

inputs amplify the AC portion of the current signal to the

IC’s current comparator.

SNS1–/SNS2–/SNS3–/SNS4– (Pins 14, 17, 44, 47):

Negative Current Sense Comparator Inputs. The nega-

tive input of the current comparator is normally connected

to the VLOW.

SNSD1+/SNSD2+/SNSD3+/SNSD4+ (Pins 15, 16, 45,

46): DC Positive Current Sense Comparator Inputs. These

inputs amplify the DC portion of the current signal to the

IC’s current comparators and current sense amplifiers.

RUN (Pin 19): 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 thresh-

old, the pull-up current increases to 6µA.

PWMEN (Pin 20): Enable Pin for External Gate Drivers.

Open drain logic that is pulled to ground when the

LTC7872 shut downs the external gate drivers. When this

pin is low, all the PWM pin outputs are high impedance.

PWM1, PWM2, PWM3, PWM4 (Pins 21, 23, 24, 26):

(Top) Gate Signal Output. This signal goes to the PWM

or top gate input of the external gate driver or integrated

driver MOSFET. This is a three-state compatible output.

PGOOD (Pin 22): Power Good Indictor Output for the

Regulated VHIGH/VLOW. Open drain logic out that is pulled

to ground when the regulated VHIGH/VLOW exceeds ±10%

regulation window, after the internal 40µS power bad

mask timer expires.

FAULT (Pin 25): Fault Indicator Output. Open-drain output

that pulls to ground during a fault condition.

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