ASM805LCPA PULSECORE [PulseCore Semiconductor], ASM805LCPA Datasheet - Page 4

• Manufacturer Part Number: ASM805LCPA
• Description: ?P Power Supply Supervisor With Battery Backup Switch
• Manufacturer: PULSECORE [PulseCore Semiconductor]

April 2008
rev 1.7
Watchdog Input
As discussed in the Reset section, the Watchdog input is
used to monitor microprocessor activity. It can be used to
insure that the microprocessor is in a continually
responsive state by requiring that the WDI pin be toggled
every second. If the WDI pin is not toggled within the 1.6
second window (minimum t
asserted to return the microprocessor to the initial
start-up state. Pulses as short as 50ns can be applied to
the WDI pin. If this feature is not used, the WDI pin
should be open circuited or the logic placed into a high-
impedance state to allow the pin to float.
Backup-Battery Switchover
A power loss can be made less severe if the system RAM
contents are preserved. This is achieved in the
ASM690/692/ 802/805 by switching from the failed V
an alternate power source connected at V
is less than the reset threshold voltage (V
V
connected to V
brown-out or loss of V
by means of a 20Ω PMOS switch. Although both
conditions (V
the switchover to V
back to V
voltage at V
device diode (D1 in Figure 3) will be forward biased if
V
is switched to V
that V
ASM690A/802A/805L Reset Threshold = 4.65V
ASM692A /ASM802M Reset Threshold = 4.4V
CC
BATT
V
V
V
CC
CC
CC
is less than V
BATT
exceeds V
> Reset Threshold
< Reset Threshold
< Reset Threshold
V
V
Condition
CC
CC
CC
be no greater than V
> V
< V
CC
BATT
when V
BATT
BATT
CC
OUT
< V
CC
. It should be noted that an internal
BATT
by more than a diode drop when V
. Because of this it is recommended
through a 2Ω PMOS switch but a
RT
µP Power Supply Supervisor With Battery Backup Switch
CC
BATT
CC
and V
exceeds V
will cause a switchover to V
to occur, V
. The V
WD
CC
+ t
SW1/SW2
RT
Closed
RS
Open
Open
<V
Notice: The information in this document is subject to change without notice.
+0.6V.
), a reset pulse will be
RT
OUT
BATT
OUT
irrespective of the
) must occur for
pin is normally
will be switched
BATT
CC
SW3/SW4
< V
Closed
Closed
when V
Open
RT
), and
CC
BATT
CC
CC
to
Table 1. Pin Connections in Battery Backup Mode
During the backup power mode, the internal circuitry of
the supervisory circuit draws power from the battery
supply. While V
remain alive and the current drawn by the device is
typically 35µA. When V
V
comparator and WDI comparator will shut off, reducing
the quiescent current drawn by the IC to less than 1µA.
Backup Power Sources - Batteries
Battery voltage selection is important to insure that the
battery does not discharge through the parasitic device
diode D1 (see Figure 3) when V
V
BATT
CC
RESET
V
V
>V
PFO
WDI
Pin
PFI
BATT
, the internal switchover comparator, the PFI
OUT
RT
.
CC
Connected to V
PMOS switch
Connected to V
Disabled
Logic-LOW
Logic-LOW (except on ASM805 where
it is HIGH)
Watchdog timer disabled
is still alive, the comparator circuits
CC
drops more than 1.1V below
ASM690A/692A
ASM802L/802M
Connection
CC
BATT
OUT
is less than V
through internal
ASM805L
4 of 15
BATT
and