CALIFORNIA MICRO DEVICES
Interface Signals
V
CC
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.
The voltage level on V
CC
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 V
CC
is deselected
prior to dropout, which prevents loss of output regulation
when switching between V
CC
and V
SBY
. Typically the threshold
is set to 4.2V. Once V
CC
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 V
CC
being selected once the voltage level exceeds 4.50V
(typically).
V
SBY
is the standby 5V supply power source, which is given
priority when V
CC
is not present. The internal regulator will
remain enabled until such time that V
SBY
falls below the
disable threshold level (4.2V typically). If the V
SBY
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.
CMPWR300
V
AUX
is the auxiliary low voltage power source. This supply
is only used when neither the V
CC
nor V
SBY
is available. Under
these conditions an internal switch is enabled and provides
a very low impedance connection directly between V
OUT
and V
AUX
.
V
OUT
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.
GND
provides the reference for all voltages.
INTERFACE SIGNALS
Pin
1
2
3
4
5 -8
Symbol
V
SBY
V
CC
V
OUT
V
AUX
GN D
D escription
Standby supply voltage (5V) input for regulator when V
CC
falls below 4.2V.
Primary supply voltage (5V) input for regulator.
Regulator voltage output (3.3V) regulator when either V
CC
or V
SBY
is present.
Auxiliary supply voltage (3.3V) input for low impedence switch.
Reference for all voltages.
© 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 ]
