AS1322 datasheet(2/17 Pages) AMSCO

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AS1322

Data Sheet - Pi n Assignments

4 Pin Assignments

Figure 2. Pin Assignments (Top View)

Pin Descriptions

Table 2. Pin Descriptions

Name

Number

Description

Switch Pin. Connect an inductor between this pin and VIN. Keep the PCB

trace lengths as short and wide as is practical to reduce EMI and voltage

overshoot. If the inductor current falls to zero, or pin SHDNN is low, an

internal 100

Ω anti-ringing switch is connected from this pin to VIN to

minimize EMI.

Note: An optional Schottky diode can be connected between this pin and

VOUT.

GND

Signal and Power Ground. Provide a short, direct PCB path between this

pin and the negative side of the output capacitor(s).

Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor

divider tap to this pin. The output voltage can be adjusted from 2.5 to 5V by:

VOUT = 1.23V[1 + (R1/R2)]

SHDNN

Shutdown Pin. Logic controlled shutdown input.

1 = Normal operation, 1.2MHz typical operating frequency.

0 = Shutdown; quiescent current <1µA. If SHDNN is undefined, pin SW may

ring.

Note: In a typical application, SHDNN should be connected to VIN through a

Ω pull-up resistor.

VOUT

Output Voltage Sense Input and Drain of the Internal PMOS

Synchronous Rectifier. Bias is derived from VOUT when VOUT exceeds VIN.

PCB trace length from VOUT to the output filter capacitor(s) should be as

short and wide as is practical. VOUT is held at approximately VIN - 0.6V

during shutdown.

VIN

Input Voltage. The AS1322 gets its start-up bias from VIN unless VOUT

exceeds VIN, in which case the bias is derived from VOUT. Thus, once

started, operation is completely independent from VIN. Operation is only

limited by the output power level and the internal series resistance of the

supply.

AS1322

GND

6 VIN

5 VOUT

4 SHDNN

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