TC1240_13 datasheet(7/18 Pages) MICROCHIP

7 / 18 page

 2001-2012 Microchip Technology Inc.

DS21516D-page 7

TC1240/TC1240A

4.0

DETAILED DESCRIPTION

The TC1240/TC1240A charge pump converter dou-

bles the voltage applied to the VIN pin. Conversion con-

sists of a two-phase operation (Figure 4-1). During the

first phase, switches S2 and S4 are open and S1 and S3

are closed. During this time, C1 charges to the voltage

on VIN and load current is supplied from C2. During the

second phase, S2 and S4 are closed, while S1 and S3

are open.

During this second phase, C1 is level-shifted upward by

VIN volts. This connects C1 to the reservoir capacitor

C2, allowing energy to be delivered to the output as

needed. The actual voltage is slightly lower than 2 x VIN

since the four switches (S1-S4) have an on-resistance

and the load drains charge from reservoir capacitor C2.

FIGURE 4-1:

Ideal Switched Capacitor

Charge Pump Doubler.

5.0

TYPICAL APPLICATIONS

5.1

Output Voltage Considerations

The TC1240/TC1240A performs voltage doubling but

does not provide regulation. The output voltage will

droop in a linear manner with respect to load current.

The value of this equivalent output resistance is approx-

imately 12

 nominal at +25°C and V

IN = +5.0V for the

TC1240A and 17

 nominal at +25°C and V

IN = +2.8V

for the TC1240. VOUT is approximately +10.0V at light

loads for the TC1240A and +5.6V for the TC1240, and

droops according to the equation below:

EQUATION

5.2

Charge Pump Efficiency

The overall power efficiency of the charge pump is

affected by four factors:

Losses from power consumed by the internal

oscillator, switch drive, etc. (which vary with

input

voltage,

temperature

and

oscillator

frequency).

I2R losses due to the on-resistance of the

MOSFET switches on-board the charge pump.

Charge pump capacitor losses due to effective

series resistance (ESR).

Losses that occur during charge transfer (from

commutation capacitor to the output capacitor)

when a voltage difference between the two

capacitors exist.

Most of the conversion losses are due to factors (2) and

(3) above. These losses are given by Equation 5-1.

EQUATION 5-1:

VOUT = 2 x VIN

TC1240/TC1240A

VIN

OSC

VIN

OUT

DROOP

–



DROOP

OUT



LOSS(2,3)

OUT



OUT

SW C1



----------------------

SWITCH

4ESR

ESR

TC1240 датащи(PDF) 7 Page - Microchip Technology

TC1240 датащи(HTML) 7 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

датащи скачать

ссылки URL