VRG8691 datasheet(7/10 Pages) AEROFLEX

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SCD8691 Rev H 11/12/13

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FIGURE 6 – SLOW START

VRG8691/92

VIN

VOUT

VSENSE

CURR. LIMIT

ENABLE

0.1µF

47µF

VBIAS

SLOW START

VBIAS

VIN

GND

0.1µF

CSS

ENABLE

If it is desirable to control the output rise time, a capacitor (CSS) can be asserted on the Slow Start pin to adjust the rise

time for the following:

A. Large load capacitance will cause high surge currents which will trip the current limit circuitry.

The use of CSS will allow the output voltage to rise slowly thus mitigate the surge current phenomenon.

B. CSS may be used solely to control VOUT RISE TIME (Tr), when CLOAD is not an issue.

C. CSS is effective only when VIN is applied prior to VBIAS or ENABLE.

CSS

CLOAD

(0.4 X 0.0014)

VOUT NOM

ICL - ILOAD NOM

Note: CSS in Farads and TR in seconds.

TR =

CSS X 2.5

0.0014

()

APPLICATION NOTE 4

VOUT START UP RISE TIME CONTROL

Utilizing the Slow Start option:

When the VRG8691/92 is first powered up, using the Slow Start function controls the rate at which VOUT rises to the

required voltage set by R1 and R2.

Note: VIN should be applied before VBIAS when the Slow Start feature is used.

VREF (=1V)

IADJ

CLOAD

47µF

VOUT

TANT

1µF

TANT

CER

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