Circuit Description: continued
based applications. RC values can be chosen using the
following formula:
ÐtDelay
VOUT
5V to mP
and
RTOTCRST
=
System
Power
VT Ð VOUT
VRST Ð VOUT
C
ln
OUT
R
[
]
RST
CS8101
)
(
to mP
RESET
Port
RESET
RESET
where: RRST
=
Delay resistor
C
RST
RIN = µP port impedance
RTOT = RRST in parallel with RIN
RESET
Delay capacitor
CRST
tDelay = desired delay time
RESET
=
Figure 3. RC Network for RESET Delay
VRST = VSAT of
lead (0.7V @ turn - ON)
threshold
RESET
An external RC network on the
lead (Figure 3) pro-
RESET
VT
=
vides a sufficiently long delay for most microprocessor
Applications Notes
VIN
VOUT
V
V
CC
BAT
0.1mF
C
OUT
R
500kW
mP
RST
CS8101
RESET
RESET
ENABLE
Gnd
I/O Port
C
RST
Q
1
100kW
500kW
100kW
SWITCH
Figure 4. Microprocessor Control of CS8101 using external switching transistor Q .
1
The circuit depicted in Figure 4 lets the microprocessor
ENABLE
By coupling these two controls with the
lead, the
control its power source, the CS8101 regulator. An I/O
port on the µP and the SWITCH port are used to drive the
base of Q1. When Q1 is driven into saturation, the voltage
system has added flexibility. Once the system is running,
the state of the SWITCH is irrelevant as long as the I/O
port continues to drive Q1. The microprocessor can turn
off its own power by withdrawing drive current, once the
SWITCH is open. This software control at the I/O port
allows the microprocessor to finish key housekeeping
functions before power is removed.
ENABLE
on the
lead falls below its lower threshold. The
regulatorÕs output is
removed, the voltage on the
. When the drive current is
enabled
ENABLE
lead rises, the out-
put is switched off and the IC moves into Sleep mode
where it draws 50µA (max).
The logic options are summarized in Table 1.
4
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
