MAX793SCSE+T Maxim Integrated Products, MAX793SCSE+T Datasheet - Page 14

• Manufacturer Part Number: MAX793SCSE+T
• Description: IC SUPERVISOR MPU 16-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Battery Backup Circuitr

Specifications of MAX793SCSE+T

• Number Of Voltages Monitored: 1
• Output: Open Drain, Push-Pull
• Reset: Active High/Active Low
• Reset Timeout: 140 ms Minimum
• Voltage - Threshold: 2.925V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
Figure 12. Using the Power-Fail Comparator to Monitor an Additional Power Supply: (a) V
The power-fail comparator turns off and PFO goes low
when V
first half of the reset timeout period (t
high, irrespective of V
ond half of t
and PFO follows PFI. If the comparator is unused, con-
nect PFI to V
be connected to MR so that a low voltage on PFI gener-
ates a reset (Figure 12b). In this configuration, when
the monitored voltage causes PFI to fall below V
PFO pulls MR low, causing a reset to be asserted.
Reset remains asserted as long as PFO holds MR low,
and for 200ms after PFO pulls MR high when the moni-
tored supply is above the programmed threshold.
In the event of a brownout or power failure, it may be
necessary to preserve the contents of RAM. With a
backup battery installed at BATT, the devices automati-
cally switch RAM to backup power when V
order to allow the backup battery (e.g., a 3.6V lithium
cell) to have a higher voltage than V
supervisors (designed for 3.3V and 3V systems) does
not always connect BATT to OUT when V
greater than V
140Ω switch) either when V
14
(a)
______________________________________________________________________________________
PFO
V
V
TRIP
CC
CC
V
L
= R2
= R2
falls below V
R1
R2
RP
CC
V
(V
(V
IN
PFT
PFT
CC
, the power-fail comparator is enabled
and leave PFO unconnected. PFO can
)
+ V
(
. BATT connects to OUT (through a
PFH
1
R1
Backup-Battery Switchover
+
)
(
PFI
R2
1
R1
1
SW
)
. At the beginning of the sec-
+
–
PFI
R2
1
V
on power-down. During the
R1
CC
V
L
)
CC
–
MAX793
MAX794
V
CC
R1
V
V
GND
TRIP
falls below V
CC
CC
3.0V OR 3.3V
RP
WHERE
, this family of µP
NOTE: V
), PFO is forced
PFO
0V
TRIP,
V
V
CC
PFT
PFH
V
= 1.237V
= 10mV
L
falls. In
SW
BATT
ARE NEGATIVE
V
IN
PFT
and
is
,
V
1.75V (typ) regardless of the BATT voltage.
Switchover at V
entered before V
mum required to reliably retain data in most CMOS
RAM, (switchover at higher V
decrease backup-battery life). When V
switchover is deferred either until V
V
reset threshold (V
power-up switchover technique prevents V
charging the backup battery through OUT when using
an external transistor driven by BATT ON. OUT con-
nects to V
when V
BATT ON is high when OUT is connected to BATT.
Although BATT ON can be used as a logic output to
indicate the battery switchover status, it is most often
used as a gate or base drive for an external pass tran-
sistor for high-current applications (see Driving an
External Switch with BATT ON in the Applications
Information section). When V
power-up, BATT ON sinks 3.2mA at 0.4V. In battery-
backup mode, this terminal sources 100µA from BATT.
(b)
BATT
BATT
PFO
V
CC
is greater than V
CC
is below V
V
V
H
TRIP
= (V
CC
R1
R2
crosses the reset threshold (Figure 13).
=
PFT
V
V
PFT
IN
through a 4Ω (max) PMOS power switch
+ V
SW
(
PFH
R1
OUT
IN
R2
+ R2
)
RST
ensures that battery-backup mode is
BATT ON (MAX793/MAX794)
RST
(
Is Negative, (b) V
R1
)
R2
, or when V
+ R2
gets too close to the 2.0V mini-
) if V
V
CC
PFI
TRIP
)
, or when V
BATT
V
MAX793
MAX794
H
V
GND
CC
CC
CC
is above V
CC
IN
3.0V OR 3.3V
CC
exceeds V
Is Positive
voltages would
rises above the
crosses V
PFO
CC
MR
CC
falls below
recovers,
RST
CC
RST
BATT
V
. This
IN
from
on
if