參數(shù)資料
型號(hào)： LTC693
廠商： Linear Technology Corporation
英文描述： Microprocessor Supervisory Circuits(μP監(jiān)控電路)
中文描述： 微處理器監(jiān)控電路（微處理器監(jiān)控電路）
文件頁(yè)數(shù)： 9/16頁(yè)
文件大?。?/td> 261K
代理商： LTC693
9
LTC692/LTC693
memory backup instead of a battery. The charging resistor
for the rechargeable batteries should be connected to
V
OUT
since this eliminates the discharge path that exists
when the resistor is connected to V
CC
(Figure 3).
Replacing the Backup Battery
When changing the backup battery with system power
on, spurious resets can occur while the battery is re-
moved due to battery standby current. Although battery
standby current is only a tiny leakage current, it can still
charge up the stray capacitance on the V
BATT
pin. The
oscillation cycle is as follows: When V
BATT
reaches within
50mV of V
CC
, the LTC692/LTC693 switch to battery
backup. V
OUT
pulls V
BATT
low and the devices go back to
normal operation. The leakage current then charges up
the V
BATT
pin again and the cycle repeats.
If spurious resets during battery replacement pose no
problems, then no action is required. Otherwise, a resistor
from V
BATT
to GND will hold the pin low while changing the
battery. For example, the battery standby current is 1
μ
A
maximum over temperature and the external resistor
required to hold V
BATT
below V
CC
is:
V
– 50mV
1 A
With V
CC
= 4.25V, a 3.9M resistor will work. With a 3V
battery, this resistor will draw only 0.77
μ
A from the
battery, which is negligible in most cases.
U
S
A
O
PPLICATI
U
U
The LTC692/LTC693 are protected for safe area operation
with a short circuit limit. Output current is limited to
approximately 200mA. If the device is overloaded for long
periods of time, thermal shutdown turns the power switch
off until the device cools down. The threshhold tempera-
ture for thermal shutdown is approximately 155
°
C with
about 10
°
C of hysteresis which prevents the device from
oscillating in and out of shutdown.
The PNP switch used in competitive devices was not
chosen for the internal power switch because it injects
unwanted current into the substrate. This current is col-
lected by the V
BATT
pin in competitive devices and adds to
the charging current of the battery which can damage
lithium batteries. The LTC692/LTC693 use a charge pumped
NMOS power switch to eliminate unwanted charging
current while achieving low dropout and low supply cur-
rent. Since no current goes to the substrate, the current
collected by the V
BATT
pin is strictly junction leakage.
A 125
PMOS switch connects the V
BATT
input to V
OUT
in
battery backup mode. The switch is designed for very low
dropout voltage (input-to-output differential). This feature
is advantageous for low current applications such as
battery backup in CMOS RAM and other low power CMOS
circuitry. The supply current in battery backup mode is
1
μ
A maximum.
The operating voltage at the V
BATT
pin ranges from 2.0V to
4.0V. High value capacitors, such as electrolytic or farad-
size double layer capacitors, can be used for short term
Figure 2. Using BATT ON to Drive External PNP Transistor
5V
3V
0.1μF
0.1μF
V
BATT
V
CC
LTC693
V
OUT
GND
4
3
1
2
5
ANY PNP POWER TRANSISTOR
LTC692/3 F02
BATT ON
Figure 3. Charging External Battery Through V
OUT
5V
3V
0.1μF
0.1μF
LTC692/3 F03
V
OUT
– V
BATT
R
I =
R
V
BATT
V
CC
LTC692
LTC693
V
OUT
GND
R
CC
≤
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