MAX793SCSE+C48 Maxim Integrated, MAX793SCSE+C48 Datasheet - Page 10

• Manufacturer Part Number: MAX793SCSE+C48
• Description: Supervisory Circuits 3.0V/3.3V Adjustable Microprocessor Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX793, MAX793R, MAX793S, MAX793T, MAX794, MAX795, MAX795R, MAX795S, MAX795Tr

Specifications of MAX793SCSE+C48

• Number Of Voltages Monitored: 1
• Monitored Voltage: 3 V, 3.3 V
• Output Type: Active High, Active Low, Open Drain
• Manual Reset: Resettable
• Watchdog: Watchdog
• Battery Backup Switching: Backup
• Supply Voltage - Max: 5.5 V
• Chip Enable Signals: Yes
• Maximum Power Dissipation: 842 mW
• Power Fail Detection: Yes
• Supply Current (typ): 62 uA
• Supply Voltage - Min: 1 V

The MAX793T/MAX795T are intended for 3.3V systems
with a ±5% power-supply tolerance and a 10% systems
tolerance. Except when MR is asserted, reset does not
assert as long as the power supply remains above
3.15V (3.3V - 5%). Reset is guaranteed to assert before
the power supply falls below 3.0V (3.3V - 10%).
The MAX793S/MAX795S are designed for 3.3V ±10%
power supplies. Except when MR is asserted, they are
guaranteed not to assert reset as long as the supply
remains above 3.0V (3.0V is just above 3.3V - 10%).
Reset is guaranteed to assert before the power supply
falls below 2.85V (3.3V - 14%).
The MAX793R/MAX795R are optimized to monitor 3.0V
±10% power supplies. Reset does not occur until V
falls below 2.7V (3.0V - 10%), but is guaranteed to
occur before the supply falls below 2.55V (3.0V - 15%).
Program the MAX794’s reset threshold with an external
voltage divider to RESET IN. The reset-threshold toler-
ance is a combination of the RESET IN tolerance and
the tolerance of the resistors used to make the external
voltage divider. Calculate the reset threshold as follows:
3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
Figure 3. MAX794 Standard Application Circuit
10
3.6V
R1
R2
______________________________________________________________________________________
+5V
3.3V
+5V SUPPLY
FAILURE
0.1µF
0.1µF
V
RST
= V
V
BATT
RESET IN
PFO
PFI
MR
WDO
CC
RST IN
(OPTIONAL)
D
SILICONIX
Si9433DY
BATT ON
MAX794
GND
PMOS
LOWLINE
CE OUT
S
RESET
CE IN
(R1 / R2 + 1)
OUT
WDI
ADDRESS
DECODER
V
Reset Threshold
CC
CMOS
4.7kΩ
0.1µF
RAM
V
RST
= V
RST IN
(
R1 + 1
R2
I/O
NMI
A0-A15
RESET
V
CC
)
CC
Using the standard application circuit (Figure 3), the
reset threshold can be programmed anywhere in the
range of V
Reset is asserted when V
The MAX793/MAX794’s battery freshness seal discon-
nects the backup battery from internal circuitry until it is
needed. This allows an OEM to ensure that the backup
battery connected to BATT is fresh when the final prod-
uct is put to use. To enable the freshness seal, connect
a battery to BATT, ground PFO, bring V
reset threshold, and hold it there until reset is deassert-
ed following the reset timeout period, then bring V
back down again (Figure 4). Once the battery fresh-
ness seal is enabled (disconnecting the backup battery
from the internal circuitry and anything connected to
OUT), it remains enabled until V
V
fere with battery freshness seal operation.
BATT OK indicates the status of the backup battery.
When reset is not asserted, the MAX793 checks the
battery voltage continuously. If V
(2.0V min), BATT OK goes low; otherwise, it remains
pulled up to V
goes below V
In the MAX793/MAX794, the watchdog circuit monitors
the µP’s activity. If the µP does not toggle the watchdog
input (WDI) within 1.6s, WDO goes low. The internal
1.6s timer is cleared and WDO returns high either when
Figure 4. Battery Freshness Seal Enable Timing
RST
V
PFO
(EXTERNALLY HELD AT 0V)
RESET
RESET PULLED UP TO V
CC
. Note that connecting PFO to MR does not inter-
Watchdog Input (MAX793/MAX794)
SW
SW
V
CC
RST
(the battery switch threshold) to 5.5V.
.
CC
. BATT OK also goes low when V
BATT OK Output (MAX793)
CC
Battery Freshness Seal
falls below V
t
RP
CC
PFO STATE LATCHED,
FRESHNESS SEAL ENABLED.
BATT
is brought above
is below V
SW
CC
.
above the
V
RST
BOK
CC
CC