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060303
FEATURES
Power-fail detector for personal computers
and workstations
Connects directly to popular personal
computer chip sets
On chip 32.768 kHz oscillator for real time
clock
Provides battery backup power to clock chip
Pushbutton reset input
Accurate 5% or 10% +5-volt power supply
monitoring
Complementary outputs for reset, power-fail,
and low battery
Provides for reset pulse width of either 95 ms
or 190 ms
Eliminates the need for discrete components
Low-power CMOS circuitry
16-pin DIP or SOIC surface mount package
0C to 70C operation
PIN ASSIGNMENT
PIN DESCRIPTION
PBRST
- Pushbutton Reset Input
X1, X2
- Crystal Inputs
V
BAT
-
Battery
Input
LB,
LB
- Low Battery Outputs
RST,
RST
- Reset Outputs
RD
- Reset Duration
TOL
- Selects 5% Or 10% Detection
GND -
Ground
OSCOUT
- Oscillator Out
V
CCO
- Switched Power Out
PF,
PF
- Power-Fail Outputs
V
CC
- +5-Volt Power In
DESCRIPTION
The DS1632 PC Power-Fail and Reset Controller is designed to do various functions involving battery
backup and other functions typically accomplished with discrete components. The DS1632 provides a
32.768 kHz battery-backed crystal oscillator and switched V
CC
/V
BAT
power via V
CCO
for the real time
clock function located in accompanying chip sets. In addition, the DS1632 provides for reset on both
DS1632
PC Power-Fail and Reset Controller
www.maxim-ic.com
16-Pin DIP (300-mil)
See Mech. Drawings Section
PBRST
X1
X2
V
CC
PF
PF
1
2
3
16
15
14
V
BAT
V
CCO
4
13
LB
LB
TOL
RST
RST
RD
5
6
7
12
11
10
GND
OSCOUT
8
9
16-Pin SOIC (300-mil)
See Mech. Drawings Section
PBRST
X1
X2
V
CC
PF
PF
1
2
3
16
15
14
V
BAT
V
CCO
4
13
LB
LB
TOL
RST
RST
RD
5
6
7
12
11
10
GND
OSCOUT
8
9
DS1632
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power-up and via pushbutton input, power-fail status signals for the processor, and low battery warning
signals. The DS1632 is capable of detecting power failure at both the 5% and 10% power supply
tolerances, and the reset pulse width can be set for either 95 ms or 190 ms. The device is designed to
connect directly to popular laptop and notebook chip sets which eliminates the need for discrete
components and reduces cost.
BLOCK DIAGRAM Figure 1
OPERATION - CRYSTAL OSCILLATOR SECTION
The DS1632 crystal oscillator is designed to be hooked directly to a 32.768 kHz crystal. By using the
Daiwa Part No. DT26S, Seiko Part No. DS-VT-200 or equivalent, the oscillator will be accurate enough
to run a real time clock to within 2 minutes per month. If another crystal is to be selected, it should have
a specified load capacitance (C
L
) of 6 pF. The crystal oscillator will run as long as either V
CC
or V
BAT
is
present, providing that V
BAT
is greater than 2.3V. The oscillator output provides a rail to rail swing with
regards to V
CC
or V
BAT
, whichever is greater. The crystal oscillator is also used internally as a time base.
DS1632
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OPERATION POWER-FAIL, BATTERY BACKUP
The DS1632 provides a switch to direct power from the battery (V
BAT
) or the incoming supply (V
CC
),
depending on which is greater. This switch has a voltage drop of less than 0.3 volts. The V
CC
input is
constantly monitored by a precision comparator for an out-of-tolerance condition. When such a condition
occurs, the power-fail signals are driven to their active state immediately. The reset signals are also driven
active, but this action is delayed by a time determined by the level of the input on the reset duration pin
(RD). If RD is tied to ground then reset signals will become active after 9 ms. If RD is tied to V
CC
, then
reset signals will become active after 18 ms. Once active, both the reset signals and the power-fail signals
will remain active as long as a (V
CC
) out-of-tolerance condition persists. If an out-of-tolerance condition
is not long enough to activate the reset signals, then only the power-fail signals would be affected. When
power returns to within nominal limits the power-fail signals will return immediately to the inactive state.
However, the reset signals remain in the active state for a time which is dependent on the state of the RD
pin. If RD is tied to ground, the reset signals will remain active for 95 ms. If RD is tied to V
CC
, then the
reset signals will remain active for 190 ms after power is within nominal limits. The delay action on the
reset signals allows time for the power supply and microprocessor clock oscillators to stabilize. The
tolerance pin (TOL) selects the point at which power-fail detection occurs. With the tolerance pin
grounded, power-fail detection occurs in the range of 4.75V to 4.5V. If the tolerance pin is connected to
V
CC
, then power-fail detection occurs in the range of 4.5V to 4.25V. During most power supply
conditions the V
CC
input will supply power to all functions within the chip and also to the V
CCO
pin. The
battery pin (V
BAT
) only supplies power when V
CC
is less than V
BAT
. When V
CC
is below the level of V
BAT
only the V
CCO
and the OSC OUT pin remain powered by V
BAT
. All other outputs will be driven to ground
when in a logic low state and will be driven to V
CC
when in a logic high state. This is done to preserve
battery capacity by avoiding battery drain resulting from loads on these outputs. The output ground level
will be maintained for all levels of V
CC
, even V
CC
= GND. However, the output V
CC
level will be
maintained only for V
CC
> 2.0V. Internal battery power consumption is less than 2
mA while V
BAT
is
supplying power. The external load on OSC OUT and V
CCO
must be added to internal consumption to
determine the total load on the battery.
OPERATION - PUSHBUTTON RESET
The DS1632 provides an input pin for direct connection to a pushbutton. The pushbutton reset input
PBRST
requires an active low level input. While TTL levels are sufficient to properly activate this input,
it has been primarily designed for contact closure. Internally, this input is debounced and timed such that
RST and
RST
signals of 95ms or 190 ms minimum are generated. If RD is tied to ground, then a reset
pulse of 95 ms is generated. If RD is tied to V
CC
then a reset pulse of 190 ms is generated. The delay time
is started as the pushbutton reset input is released from low level.
OPERATION - LOW BATTERY WARNING
The DS1632 provides outputs which warn of a low battery condition. Whenever V
CC
is within nominal
limits, the V
BAT
input is continuously monitored. If the V
BAT
input is out of tolerance, the low battery
outputs are driven to their active states, and will remain in the active state as long as V
CC
is within
nominal limits or until the battery input is restored to an in limit status. On power-up, if the V
BAT
input is
out of tolerance, the low battery outputs are not guaranteed active until power-fail is deactivated, but
guaranteed active prior to reset inactive. When V
CC
is below the V
CC
fail trip point both LB and LB will
be driven to ground.
For application information, please reference Application Note 64, published separately.
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