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LTC1436A

High Efficiency Low Noise Synchronous Step-Down Switching Regulators

Linear Technology 

LTC1436A

LTC1436A-PLL/LTC1437A

TYPICAL PERFORMANCE CHARACTERISTICS

Auxiliary Regulator

Sink Current Available

20

15

10

5

0

0 2 4 6 8 10 12 14 16

AUX DR VOLTAGE (V)

1436 G19

Auxiliary Regulator PSRR

70

10mA LOAD

60

50

100mA LOAD

40

30

20

10

10

100

FREQUENCY (kHz)

1000

1436 G20

PIN FUNCTIONS

VIN: Main Supply Pin. Must be closely decoupled to the

IC’s signal ground pin.

INTVCC: Output of the Internal 5V Regulator and EXTVCC

Switch. The driver and control circuits are powered from

this voltage. Must be closely decoupled to power ground

with a minimum of 2.2µF tantalum or electrolytic capacitor.

DRVCC: Bottom MOSFET Driver Supply Voltage.

EXTVCC: Input to the Internal Switch Connected to INTVCC.

This switch closes and supplies VCC power whenever

EXTVCC is higher than 4.7V. See EXTVCC connection in

Applications Information section. Do not exceed 10V on

this pin. Connect to VOUT if VOUT ≥ 5V.

BOOST: Supply to Topside Floating Driver. The bootstrap

capacitor is returned to this pin. Voltage swing at this pin

is from INTVCC to VIN + INTVCC.

SW: Switch Node Connection to Inductor. Voltage swing

at this pin is from a Schottky diode (external) voltage drop

below ground to VIN.

SGND: Small Signal Ground. Must be routed separately

from other grounds to the (–) terminal of COUT.

PGND: Driver Power Ground. Connects to source of

bottom N-channel MOSFET and the (–) terminal of CIN.

SENSE –: The (–) Input to the Current Comparator.

SENSE +: The (+) Input to the Current Comparator. Built-

in offsets between SENSE– and SENSE+ pins in conjunction

with RSENSE set the current trip thresholds.

VOSENSE: Receives the remotely sensed feedback voltage

either from the output or from an external resistive divider

across the output . The VPROG pin determines which point

VOSENSE must connect to.

VPROG: This voltage selects the output voltage. For VPROG

< VINTVCC/3 the output is set to 3.3V with VOSENSE

connected to the output. With VPROG > VINTVCC/1.5 the

output is set to 5V with VOSENSE connected to the output.

Leaving VPROG open (DC) allows the output voltage to be

set by an external resistive divider connected to VOSENSE.

COSC: External capacitor COSC from this pin to ground sets

the operating frequency.

ITH: Error Amplifier Compensation Point. The current

comparator threshold increases with this control voltage.

Nominal voltage range for this pin is 0V to 2.5V.

RUN/SS: Combination of Soft Start and Run Control

Inputs. A capacitor to ground at this pin sets the ramp time

to full current output. The time is approximately 0.5s/µF.

7

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