LTC1435ACS datasheet(5/20 Pages) LINER

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LTC1435A

TYPICAL PERFORMANCE CHARACTERISTICS

Soft Start: Load Current vs Time

Burst Mode Operation

PIN FUNCTIONS

ever 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.

PGND (Pin 10): Driver Power Ground. Connects to source

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

BG (Pin 11): High Current Gate Drive for Bottom

N-Channel MOSFET. Voltage swing at this pin is from

ground to INTVCC.

INTVCC (Pin 12): Output of the Internal 5V Regulator and

EXTVCC Switch. The driver and control circuits are pow-

ered from this voltage. Must be closely decoupled to power

ground with a minimum of 2.2

µF tantalum or electrolytic

capacitor.

VIN (Pin 13): Main Supply Pin. Must be closely decoupled

to the IC’s signal ground pin.

SW (Pin 14): Switch Node Connection to Inductor. Volt-

age swing at this pin is from a Schottky diode (external)

voltage drop below ground to VIN.

BOOST (Pin 15): Supply to Topside Floating Driver. The

bootstrap capacitor is returned to this pin. Voltage swing

at this pin is from INTVCC to VIN + INTVCC.

TG (Pin 16): High Current Gate Drive for Top N-Channel

MOSFET. This is the output of a floating driver with a

voltage swing equal to INTVCC superimposed on the

switch node voltage SW.

COSC (Pin 1): External capacitor COSC from this pin to

ground sets the operating frequency.

RUN/SS (Pin 2): 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. Forcing this pin below 1.3V causes the device to

be shut down. In shutdown all functions are disabled.

ITH (Pin 3): Error Amplifier Compensation Point. The

current comparator threshold increases with this control

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

SFB (Pin 4): Secondary Winding Feedback Input. Nor-

mally connected to a feedback resistive divider from the

secondary winding. This pin should be tied to: ground to

force continuous operation; INTVCC in applications that

don’t use a secondary winding; and a resistive divider from

the output in applications using a secondary winding.

SGND (Pin 5): Small-Signal Ground. Must be routed

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

VOSENSE (Pin 6): Receives the feedback voltage from an

external resistive divider across the output.

SENSE – (Pin 7): The (–) Input to the Current Comparator.

SENSE + (Pin 8): The (+) Input to the Current Comparator.

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

conjunction with RSENSE set the current trip thresholds.

EXTVCC (Pin 9): Input to the Internal Switch Connected to

INTVCC. This switch closes and supplies VCC power when-

ILOAD = 50mA

1435A G16

VOUT

20mV/DIV

VITH

200mV/DIV

1435A G17

RUN/SS

5V/DIV

INDUCTOR

CURRENT

1A/DIV

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