CALIFORNIA MICRO DEVICES
CMPWR300
Interface Signals
V
AUX is the auxiliary low voltage power source. This supply
VCC is the primary power source which is given priority when
present. If this connection is made within a few inches of
the main input filter, a bypass capacitor may not be necessary.
Otherwise a bypass filter capacitor in the range of 1µF to
10µF will ensure adequate filtering.
is only used when neither the VCC nor VSBY is available. Under
these conditions an internal switch is enabled and provides
a very low impedance connection directly between VOUT
and VAUX
.
VOUT is the output voltage. Power is provided from the
regulator or via the low impedance auxiliary switch. This
output requires a capacitance of 10µF to ensure regulator
stability and minimize the peak output disturbance during
power supply changeover.
The voltage level on VCC is compared to an internal threshold
voltage to determine which power source is to be selected.
In order to prevent regulator dropout from occurring, the
threshold has been programmed to ensure VCC is deselected
prior to dropout, which prevents loss of output regulation
when switching between VCC and VSBY. Typically the threshold
is set to 4.2V. Once VCC falls below this level, the output
voltage is immediately derived from the auxiliary power
source. To prevent chatter during this transition, the threshold
has a built-in hysteresis of 300mV which results in only VCC
being selected once the voltage level exceeds 4.50V
(typically).
GND provides the reference for all voltages.
VSBY is the standby 5V supply power source, which is given
priority when VCC is not present. The internal regulator will
remain enabled until such time that VSBY falls below the
disable threshold level (4.2V typically). If the VSBY connection
is made within a few inches of the main input filter, a bypass
capacitor may not be necessary. Otherwise a bypass filter
capacitor in the range of 1µF to 10µF will ensure adequate
filtering.
IN TE R FA C E S IG N A LS
Pin
1
Sym bol
VSBY
Description
Standby supply voltage (5V) input for regulator when VCC falls below 4.2V.
Primary supply voltage (5V) input for regulator.
2
VCC
3
VOUT
Regulator voltage output (3.3V) regulator when either VCC or VSBYis present.
Auxiliary supply voltage (3.3V) input for low impedence switch.
Reference for all voltages.
4
VAUX
GND
5-8
© 2000 Calirornia Micro Devices Corp. All rights reserved.
12/5/2000
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214
Fax: (408) 263-7846
www.calmicro.com
3
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
