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LTC1929

2-Phase, High Efficiency, Synchronous Step-Down Switching Regulators

Linear Technology 

LTC1929/LTC1929-PG

PI FU CTIO S

RUN/SS (Pin 1): Combination of Soft-Start, Run Control

Input and Short-Circuit Detection Timer. A capacitor to

ground at this pin sets the ramp time to full current output.

Forcing this pin below 0.8V causes the IC to shut down all

internal circuitry. All functions are disabled in shutdown.

SENSE1+, SENSE2+ (Pins 2,14): The (+) Input to the

Differential Current Comparators. The ITH pin voltage and

built-in offsets between SENSE– and SENSE+ pins in

conjunction with RSENSE set the current trip threshold.

SENSE1–, SENSE2– (Pins 3, 13): The (–) Input to the

Differential Current Comparators.

EAIN (Pin 4): Input to the Error Amplifier that compares

the feedback voltage to the internal 0.8V reference voltage.

This pin is normally connected to a resistive divider from

the output of the differential amplifier (DIFFOUT).

PLLFLTR (Pin 5): The Phase-Locked Loop’s Low Pass

Filter is tied to this pin. Alternatively, this pin can be driven

with an AC or DC voltage source to vary the frequency of

the internal oscillator.

PLLIN (Pin 6): External Synchronization Input to Phase

Detector. This pin is internally terminated to SGND with

50kΩ. The phase-locked loop will force the rising top gate

signal of controller 1 to be synchronized with the rising

edge of the PLLIN signal.

NC (Pins 7, 28): Not connected.

ITH (Pin 8): Error Amplifier Output and Switching Regula-

tor Compensation Point. Both current comparator’s thresh-

olds increase with this control voltage. The normal voltage

range of this pin is from 0V to 2.4V

SGND (Pin 9): Signal Ground, common to both control-

lers, must be routed separately from the input switched

current ground path to the common (–) terminal(s) of the

COUT capacitor(s).

VDIFFOUT (Pin 10): Output of a Differential Amplifier that

provides true remote output voltage sensing. This pin

normally drives an external resistive divider that sets the

output voltage.

VOS–, VOS+ (Pins 11, 12): Inputs to an Operational

Amplifier. Internal precision resistors capable of being

electronically switched in or out can configure it as a

differential amplifier (default for the LTC1929-PG) or an

uncommitted Op Amp.

AMPMD (Pin 15): (LTC1929 Only) This Logic Input pin

controls the connections of internal precision resistors

that configure the operational amplifier as a unity-gain

differential amplifier.

PGOOD (Pin 15): (LTC1929-PG Only) Open-Drain Logic

Output. PGOOD is pulled to ground when the voltage on

the EAIN pin is not within ±7.5% of its set point.

TG2, TG1 (Pins 16, 27): High Current Gate Drives for Top

N-Channel MOSFETS. These are the outputs of floating

drivers with a voltage swing equal to INTVCC superim-

posed on the switch node voltage SW.

SW2, SW1 (Pins 17, 26): Switch Node Connections to

Inductors. Voltage swing at these pins is from a Schottky

diode (external) voltage drop below ground to VIN.

BOOST2, BOOST1 (Pins 18, 25): Bootstrapped Supplies

to the Topside Floating Drivers. Capacitors are connected

between the Boost and Switch pins, and Schottky diodes

are tied between the Boost and INTVCC pins.

BG2, BG1 (Pins 19, 23): Voltage Swing High Current Gate

Drives for Bottom Synchronous N-Channel MOSFETS.

Voltage swing at these pins is from ground to INTVCC.

PGND (Pin 20): Driver Power Ground. Connects to sources

of bottom N-channel MOSFETS and the (–) terminals of

CIN.

INTVCC (Pin 21): Output of the Internal 5V Linear Low

Dropout Regulator and the EXTVCC Switch. The driver and

control circuits are powered from this voltage source.

Decouple to power ground with a 1µF ceramic capacitor

placed directly adjacent to the IC and minimum of 4.7µF

additional tantalum or other low ESR capacitor.

EXTVCC (Pin 22): External Power Input to an Internal

Switch . This switch closes and supplies INTVCC, bypass-

ing the internal low dropout regulator whenever EXTVCC is

higher than 4.7V. See EXTVCC Connection in the Applica-

tions Information section. Do not exceed 7V on this pin

and ensure VEXTVCC ≤ VIN.

VIN (Pin 24): Main Supply Pin. Should be closely decoupled

to the IC’s signal ground pin.

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