LTC1433 データシートの表示（PDF） - Linear Technology

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LTC1433

450mA, Low Noise Current Mode Step-Down DC/DC Converters

Linear Technology 

LTC1433/LTC1434

PIN FUNCTIONS (LTC1433/LTC1434)

SSW (Pin 1/Pin 2): Drain of the Small P-Channel MOSFET

Switch.

BSW (Pin 3/Pin 4): Drain of the Large P-Channel MOSFET

Switch.

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

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

RUN/SS (Pin 6/Pin 7): 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 approxi-

mately 0.5s/µF. Forcing this pin below 1.3V causes all

circuitry to be shut down except the low-battery com-

parator. For input voltages above 6V this pin is clamped by

a 6V Zener (see Functional Diagram). Applying voltages

greater than 6V to this pin will cause additional current to

flow into this pin.

LBO (Pin 7/Pin 9): Open-Drain Output of an N-Channel

Pull-Down. This pin will sink current when LBI goes below

1.19V.

LBI (Pin 8/Pin 10): The (+) Input of the Low-Battery

Voltage Comparator. The (–) input is connected to the

1.19V reference. When LBI is grounded along with RUN/

SS, this comparator will shut down along with the rest of

the control circuitry. LBO will go to high impedance.

VPROG (Pin 9/Pin 11): The voltage at this pin selects the

output voltage. When VPROG = 0V or VPROG = VIN, the

output is set to 3.3V and 5V respectively, with VOSENSE

connected to the output. Leaving VPROG open (DC) allows

the output voltage to be set by an external resistive divider.

VOSENSE is then connected to the common node of the

resistive divider.

VOSENSE (Pin 10/Pin 12): This pin receives the feedback

voltage either from the output or from an external resistive

divider across the output. The VPROG pin determines at

which point VOSENSE must be connected.

VPROG = 0V

VPROG = VIN

VPROG = Open (DC)

VOUT = 3.3V

VOUT = 5V

VOUT = Adjustable

ITH (Pin 11/Pin 13): Error Amplifier Compensation Point.

The current comparator threshold increases with this

control voltage. Nominal voltage range for this pin is 0V

to 2.4V.

POR (Pin 12/Pin 14): Open-Drain Output of an N-Chan-

nel Pull-Down. This pin sinks current when the output

voltage is 7.5% out of regulation. When the output rises

to – 5% of its regulated value, the pin goes into high

impedance after 216 (65536) oscillator cycles. The POR

output is asserted when the device is in shutdown,

independent of VOUT.

COSC (Pin 13/Pin 15): External capacitor connects be-

tween this pin and ground to set the operating frequency.

PLL LPF (Pin 16 LTC1434): Output of the Phase Detector

and Control Input of the Oscillator. Normally a series RC

lowpass network is connected from this pin to ground. Tie

this pin to SGND in applications which do not use the

phase-locked loop. Can be driven by a 0V to 2.4V logic

signal for a frequency shifting option.

PLLIN (Pin 17 LTC1434): External Synchronizing Input to

the Phase Detector. This pin is internally terminated to

SGND with 50kΩ. Tie this pin to SGND in applications

which do not use the phase-locked loop.

SVIN (Pin 14/Pin 18): Main Supply for All the Control

Circuitry.

PGND (Pin 15/Pin 19): Switch Driver Ground. Connects to

the (–) terminal of CIN. Anode of the Schottky diode must

be connected close to this pin.

PWRVIN (Pin 16/Pin 20): Supply for the Internal Power

MOSFETs and Switch Drivers. Must decouple this pin

properly to ground.

NC (Pins 2, 4,/Pins 1, 3, 6, 8): No Connection.

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