MAX817LCSA Maxim Integrated Products, MAX817LCSA Datasheet - Page 12

• Manufacturer Part Number: MAX817LCSA
• Description: IC MPU SUPERVISORY CIRCUIT 8SOIC
• Manufacturer: Maxim Integrated Products
• Type: Battery Backup Circuitr

Specifications of MAX817LCSA

• Number Of Voltages Monitored: 1
• Output: Push-Pull, Totem Pole
• Reset: Active Low
• Reset Timeout: 140 ms Minimum
• Voltage - Threshold: 4.65V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: Q1785362

+5V Microprocessor Supervisory Circuits
In a brownout or power failure, it may be necessary to
preserve the contents of RAM. With a backup battery
installed at BATT, the MAX817/MAX818/MAX819 auto-
matically switch RAM to backup power when V
These devices require two conditions before switching
to battery-backup mode: 1) V
reset threshold, and 2) V
Table 1 lists the status of the inputs and outputs in bat-
tery-backup mode.
As long as V
nects to V
V
(whichever is higher) switches to OUT. When V
below V
an 80 switch.
Table 1. Input and Output Status in
Battery-Backup Mode
Figure 9. Monitoring an Additional Supply by Connecting
PFO to MR.
12
CC
SIGNAL
V
V
V
V
V
C E OUT
V2
V
R ESET
V
______________________________________________________________________________________
BATT
C E IN
OUT
falls below the reset threshold, V
WDI
CC
RST
R1
R2
CC
and V
CC
PFI
through a 5
Disconnected from V
Connected to V
PMOS switch.
Connected to V
the battery is less than 1µA, as long as
V
Logic low
Watchdog timer is disabled.
Logic high. The open-circuit voltage is equal
to V
High impedance
CC
exceeds the reset threshold, OUT con-
MAX819
OUT
BATT
< V
V
Backup-Battery Switchover
V1
CC
.
BATT
, BATT switches to OUT through
RESET
PFO
MR
- 0.2V.
CC
PMOS power switch. Once
BATT
OUT
ADDITIONAL SUPPLY RESET VOLTAGE
STATUS
must be below V
CC
. Current drawn from
V2
through an internal 80
OUT
(RESET)
RESET
must be below the
.
= 1.25
P
CC
(
R1 + R2
R2
or V
CC
CC
)
BATT
BATT
falls.
falls
.
When V
the substrate, regardless of the voltage applied to BATT
(Figure 10). During this time, the diode (D1) between
BATT and the substrate will conduct current from BATT
to V
connects to OUT, backup mode is activated and the
internal circuitry is powered from the battery (Table 1).
When V
BATT is typically 6µA. When V
below V
off and the supply current falls to less than 1µA.
The MAX817/MAX818/MAX819 are protected for typical
short-circuit conditions of 10sec or less. Shorting OUT
to ground for longer than 10sec destroys the device.
Decouple V
0.1µF capacitors as close to the device as possible.
Figure 10. Backup-Battery-Switchover Block Diagram
__________Applications Information
CC
BATT
SW1
CC
if V
CC
BATT
MAX817
MAX818
MAX819
RESET THRESHOLD = 4.65V IN MAX81_L
RESET THRESHOLD = 4.4V IN MAX81_M
V
V
V
V
V
CC
CC
CC
CC
CC
exceeds the reset threshold, it is connected to
BATT
is just below V
CC
> Reset Threshold
< Reset Threshold and
> V
< Reset Threshold and
< V
, the internal switchover comparator shuts
CONDITION
BATT
, OUT, and BATT to ground by placing
BATT
SW2
is 0.6V greater than V
SUBSTRATE
D1
OUT
BATT
SW1/SW2
D2
D3
Closed
CC
Open
Open
, the current draw from
drops to more than 1V
SW3
SW3/SW4
CC
Closed
Closed
Open
. When BATT
SW4
V
CC