2004-2013 Microchip Technology Inc. DS21876B-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 capac-
itors or low effective series resistance (ESR) tantalum
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 of 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/
ON
Semiconductor
®
http://www.onsemi.com/
Fairchild
Semiconductor
®
http://www.fairchildsemi.com/