MAX690AMJA-883B Maxim Integrated Products, Inc., MAX690AMJA-883B Datasheet - Page 8

• Manufacturer Part Number: MAX690AMJA-883B
• Description: Max690a, Max692a, Max802l, Max802m, Max805l Microprocessor Supervisory Circuits
• Manufacturer: Maxim Integrated Products, Inc.

When V
ed and the internal circuitry is powered from the battery
(Table 1). When V
drawn from V
more than 1V below V
parator shuts off and the supply current falls to less
than 1µA.
SuperCaps are capacitors with extremely high capaci-
tance values, on the order of 0.1F. Figure 4 shows a
SuperCap used as a backup power source. Do not allow
the SuperCap’s voltage to exceed the maximum reset
threshold by more than 0.6V. In Figure 4’s circuit, the
SuperCap rapidly charges to within a diode drop of V
However, after a long time, the diode leakage current will
pull the SuperCap voltage up to V
SuperCap with the MAX690A/MAX802L/MAX805L, V
may not exceed 4.75V + 0.6V = 5.35V.
Use the SuperCap circuit of Figure 5 with a MAX692A
or MAX802M and a ±10% supply. This circuit
ensures that the SuperCap only charges to V
0.5V. At the maximum V
charges up to 5.0V, only 0.5V above the maximum
reset threshold—well within the requisite 0.6V.
Microprocessor Supervisory Circuits
Figure 5. Using a SuperCap™ as a Backup Power Source with
the MAX692A/MAX802M and a +5V ±10% Supply
™SuperCap is a trademark of Baknor Industries.
8
__________Applications Information
_______________________________________________________________________________________
100k
+5V
BATT
0.1F
connects to V
BATT
Using a SuperCap™ as a Backup
+
is typically 30µA. When V
V
V
CC
BATT
CC
BATT
MAX802M
MAX692A
is just below V
GND
, the internal switchover com-
OUT
CC
, backup mode is activat-
RESET
V
of 5.5V, the SuperCap
OUT
CC
Power Source
BATT
. When using a
TO µP
TO STATIC RAM
, the current
CC
drops to
CC
CC
CC
-
.
Figure 6. Adding Hysteresis to the Power-Fail Comparator
Lithium batteries work very well as backup batteries due to
very low self-discharge rates and high energy density.
Single lithium batteries with open-circuit voltages of 3.0V to
3.6V are ideal. Any battery with an open-circuit voltage
less than the minimum reset threshold plus 0.3V can be
connected directly to the V
MAX690A/MAX692A/MAX802L/MAX802M/MAX805L with
Table 2. Allowable Backup-Battery Voltages
MAX802L/MAX805L
PFO
+5V
0V
R
PART NO.
MAX690A/
MAX692A/
MAX802M
R
1
2
V
0V
V TRIP
V IH
IN
V L 1.25
(see Using a SuperCap as a Backup Power Source
section for use with a SuperCap)
−
R 1
=
1.25/
=
Allowable Backup Power-Source
1.25/
+


C1*
5 1.25
R 1



−
R 3
R 2 || R 3
R 2
+
R 2 || R 3
R 2
TO µP
+
R 2
=
1.25
R 2
R



MAXIMUM BACKUP-BATTERY


3
PFI
PFO
V
L
VOLTAGE (V)
V
V
TRIP
IN
BATT
MAX802M
MAX692A
MAX802L
MAX805L
MAX690
4.80
4.55
V
+5V
V
GND
CC
H
*OPTIONAL
input of the
Batteries