UC5301L-S08-R datasheet(4/6 Pages) UTC

4 / 6 page

UC5301

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

4 of 6

www.unisonic.com.tw

QW-R502-602.a

DETAILED DESCRIPTION

Four switches (S1, S2, S3, and S4) incorporated in the device, which are switched in a sequence to inverter the

input supply voltage. The external capacitors determine the energy transfer and storage.

The course of voltage conversion is show in Figure. 1. When S1 and S3 are closed, C1 charges to the supply

voltage VIN. During this time interval, switches S2 and S4 are open. In the second time interval, S1 and S3 are open;

at the same time, S2 and S4 are closed, C1 is charging C2. After a number of cycles, the voltage across C2 will be

pumped to VIN. Since the anode of C2 is connected to ground, the output at the cathode of C2 equals - (VIN) under o

load current condition.

The UTC UC5301 is mainly to generate a negative supply voltage. The input supply voltage is varying from1.8V to

5V. The output characteristics of this circuit can be approximated by an ideal voltage source in series with a

resistance. The voltage source equals - (VIN).

The output resistance, ROUT, is a function of the ON resistance of the internal MOSFET switches, the oscillator

frequency, the capacitance and the ESR of both C1 and C2. Since the switching current charging and discharging

C1 is approximately twice as the output current, the effect of the ESR of the pumping capacitor C1 will be multiplied

by four in the output resistance. The output capacitor C2 is charging and discharging at a current approximately

equal to the output current, therefore, this ESR term only counts once in the output resistance. The value of ROUT is

approximately calculated in the following equation:

OSC

OUT

ESR

4ESR

≅

(RSW is the sum of the ON resistance of the internal MOSFET switches shown in Figure 1.)

Lower output resistance is dependent on higher capacitance and lower ESR capacitors.

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