AN628 APPLICATION NOTE

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Pin 9. ISENSE (Current Amplifier inverting input). This pin, is externally connected to the external network de-

scribed at CA-OUT (pin 5). To be noted that Ri and Ri' have the same value because of the high impedance

feedback network.

Pin 10. SGND (Signal ground). It has to be connected, to the pc-board GND, close the filtering reference ca-

pacitor.

Pin 11. VREF (Voltage reference). An internal bandgap circuitry, allows an accurate voltage reference. An ex-

ternal capacitor filter (from 100nF to some

µF) connected to the signal ground is recommanded (see fig. 14).

This pin can deliver up to 10mA and can be used for external needs (e.g. enable for other circuits).

Figure 14.

Pin 12. SS (Soft start). This feature avoids current overload on the external Mosfet (Q) during the ramp-up of

the output boosted voltage. An internal switch discharges the capacitor if output overvoltage or VCC undervolt-

age are detected. An internal current generator of 100

µ with the external capacitor define the soft start time

costant (see fig. 15). Because the voltage at the softstart pin acts on the E/A output (driving the multiplier with

Figure 15.

t

SS

C

ss

V

VA -OUT

I

SS

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