MCP1650 datasheet(19/28 Pages) MICROCHIP

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 2004 Microchip Technology Inc.

DS21876A-page 19

MCP1650/51/52/53

5.2.4

INPUT/OUTPUT CAPACITOR

SELECTION

There are no special requirements on the input or

output capacitor. For most applications, ceramic

capacitors or low effective series resistance (ESR) tan-

talum capacitors will provide lower output ripple voltage

than aluminum electrolytic. Care must be taken not to

exceed the manufacturer’s rated voltage or ripple cur-

rent specifications. Low-value capacitors are desired

because of cost and size, but typically result in higher

output ripple voltage.

The input capacitor size is dependant on the source

impedance

the

application.

The

hysteretic

architecture of the MCP1650/51/52/53 boost converter

can draw relatively high input current peaks at certain

line and load conditions. Small input capacitors can

produce a large ripple voltage at the input of the

converter, resulting in unsatisfactory performance.

The output capacitor plays a very important role in the

performance of

the

hysteretic

gated

oscillator

converter. In some cases, using ceramic capacitors

can result in higher output ripple voltage. This is a

result of the low ESR that ceramic capacitors exhibit.

As shown in the application schematics, 100 milli-ohms

of ESR in series with the ceramic capacitor will actually

reduce the output ripple voltage and peak input cur-

rents for some applications. The selection of the capac-

itor and ESR will largely determine the output ripple

voltage.

5.2.5

LOW BATTERY DETECTION

For low battery detection, the MCP1651 or MCP1653

device should be used. The low-battery detect feature

compares the low battery input (LBI) pin to the internal

1.22V reference. If the LBI input is below the LBI

threshold voltage, the low battery output (LBO) pin will

sink current (up to 10 mA) through the internal open-

drain MOSFET. If the LBI input voltage is above the LBI

threshold, the LBO output pin will be open or high

impedance.

5.2.6

POWER GOOD OUTPUT

For power good detection, the MCP1652 or MCP1653

device is ideal. The power good feature compares the

voltage on FB pin to the internal reference (±15%). If

the FB pin is more than 15% above or below the power

good threshold, the PG output will sink current through

the internal open-drain MOSFET. If the output of the

regulator is within ±15% of the output voltage, the PG

pin will be open or high-impedance.

5.2.7

EXTERNAL COMPONENT

MANUFACTURES

Inductors:

Sumida®

Corporation

http://www.sumida.com/

Coilcraft®

http://www.coilcraft.com

BH Electronics®

http://www.bhelectronics.com

Pulse

Engineering®

http://www.pulseeng.com/

Coiltronics®

http://www.cooperet.com/

Capacitors

MuRata®

http://www.murata.com/

Kemet®

http://www.kemet.com/

Taiyo-Yuden

http://www.taiyo-yuden.com/

AVX®

http://www.avx.com/

MOSFETs and Diodes:

International

Rectifier

http://www.irf.com/

Vishay®/Siliconix

http://www.vishay.com/com-

pany/brands/siliconix/

Semiconductor®

http://www.onsemi.com/

Fairchild

Semiconductor®

http://www.fairchildsemi.com/

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