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AV34063

1.5A,Step-Up/Down Inverting Switching Regulators

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AV34063

Note 5 : If the output switch is driven into hard saturation (non-Darlington configuration) at low switch

currents (≤300mA) and high driver currents (≥30mA), it may take up to 2.0µs to come out of sturation.

This condition will shorten the off time at frequencies ≥30KHz, and is magnified at high temperatures.

This condition does not occur with a darlington configuration, since the output switch cannot saturate.

If a non-darlington is used, the following output drive condition is recommended.

Figure13. Design Formula Table

Vsat=Saturation voltage of the output switch.

VF =Forward voltage drop of the output rectifier.

The following power supply characteristics must be chosen:

Vin -Nominal input voltage.

Vout -Desired output voltage, Vout = 1.25(1+R2/R1).

Iout - Desired output current.

Fmin -Minimum desired output switching frequency at the selected valued of Vin an Io.

Vripple(p-p) - Desired peak-to-peak output ripple voltage.In practice, the calculated capacitor

value will need to be increased due to its equivalent series resistance and board layout.The

ripple voltage should be kept to a low value since it will directiy affect the line and load

regulation.

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