參數(shù)資料
型號(hào)： LTC695ISW-3.3
廠商： LINEAR TECHNOLOGY CORP
元件分類(lèi)： 電源管理
英文描述： 3.3V Microprocessor Supervisory Circuits
中文描述： 3-CHANNEL POWER SUPPLY MANAGEMENT CKT, PDSO16
封裝： 0.300 INCH, PLASTIC, SOP-16
文件頁(yè)數(shù)： 9/16頁(yè)
文件大?。?/td> 138K
代理商： LTC695ISW-3.3
9
LTC 694-3.3/LTC 695-3.3
U
S
A
O
PPLICATI
W
U
I FOR ATIO
U
3.3V
2.4V
0.1
μ
F
0.1
μ
F
V
BATT
V
CC
LTC695-3.3
V
OUT
GND
4
3
1
2
5
ANY PNP POWER TRANSISTOR
694/5-3.3 F02
BATT ON
3.3V
2.4V
0.1
μ
F
0.1
μ
F
V
BATT
V
CC
LTC694-3.3
LTC695-3.3
V
OUT
GND
694/5-3.3 F03
V
OUT
– V
BATT
R
I =
R
Figure 2. Using BATT ON to Drive External PNP Transistor
The LTC694-3.3/LTC695-3.3 are protected for safe area
operation with short-circuit limit. Output current is limited
to approximately 200mA. If the device is overloaded for a
long period of time, thermal shutdown turns the power
switch off until the device cools down. The threshhold
temperature 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 LTC694-3.3/LTC695-3.3 use a charge-
pumped NMOS power switch to eliminate unwanted charg-
ing current while achieving low dropout and low supply
current. Since no current goes to the substrate, the current
collected by V
BATT
pin is strictly junction leakage.
A 125
PMOS switch connects the V
BATT
input to V
OUT
in
battery back-up 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 back-up in CMOS RAM and other low power CMOS
circuitry. The supply current in battery back-up mode is
1
μ
A maximum.
The operating voltage at the V
BATT
pin ranges from 1.5V to
2.75V. The charging resistor for 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).
Figure 3. Charging External Battery Through V
OUT
Replacing the Back-Up Battery
When changing the back-up battery with system power
on, spurious resets can occur while the battery is removed
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 LTC694-3.3/LTC695-3.3 switch to battery back-
up. V
OUT
pulls V
BATT
low and the device goes 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 so the external resistor re-
quired to hold V
BATT
below V
CC
is:
R
V
±50mV
1 A
CC
≤
With V
CC
= 3V, a 2.7M resistor will work. With a 2V battery,
this resistor will draw only 0.7
μ
A from the battery, which
is negligible in most cases.
If battery connections are made through long wires, a 10
to 100
series resistor and a 0.1
μ
F capacitor are recom-
mended to prevent any overshoot beyond V
CC
due to the
lead inductance (Figure 4).
相關(guān)PDF資料
PDF描述
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LTC695IN Microprocessor Supervisory Circuits
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