MAX6746 Maxim, MAX6746 Datasheet - Page 8

• Manufacturer Part Number: MAX6746
• Description: UP Reset Circuits with Capacitor-Adjustable Reset/Watchdog Timeout Delay
• Manufacturer: Maxim

where V
and V
R1 and R2 can have very high values to minimize cur-
rent consumption due to low leakage currents. Set R2
to some conveniently high value (500kΩ, for example)
and calculate R1 based on the desired reset threshold
voltage, using the following formula:
The MAX6748 and MAX6749 do not monitor V
ply voltage, therefore, V
µP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
8
Figure 4a. Watchdog Timing Diagram, WDS = GND
Figure 3. Adding an External Manual Reset Function to the
MAX6748–MAX6751
_______________________________________________________________________________________
TH
RESET
NORMAL MODE (WDS = GND)
MON_TH
R1 = R2 x (V
WDI
is the reset input threshold (1.235V). Resistors
V
V
R1
R2
OV
OV
CC
CC
V
MON_TH
is the desired reset threshold voltage
RESET IN
GND
MON_TH
CC
MAX6748
MAX6749
MAX6750
MAX6751
must be greater than 1.5V to
/V
RESET IN
V
CC
- 1) (Ω)
V
CC
t
WD
CC
sup-
guarantee RESET IN threshold accuracy and timing
performance. The MAX6748 and MAX6749 can be con-
figured to monitor V
V
The MAX6750 and MAX6751 contain both factory-
trimmed threshold voltages and an adjustable reset
threshold input, allowing the monitoring of two voltages,
V
when either of the voltages falls below it respective
threshold voltages.
Many µP-based products require manual reset capabil-
ity, to allow an operator or external logic circuitry to initi-
ate a reset. The manual reset input (MR) can connect
directly to a switch without an external pullup resistor or
debouncing network. MR is internally pulled up to V
and, therefore, can be left unconnected if unused.
MR is designed to reject fast, falling transients (typically
100ns pulses) and it must be held low for a minimum of
1µs to assert the reset output. A 0.1µF capacitor from
MR to ground provides additional noise immunity. After
MR transitions from low to high, reset remains asserted
for the duration of the reset timeout period.
A manual reset option can easily be implemented
with the MAX6748–MAX6751 by connecting a normally
open momentary switch in parallel with R2
When the switch is closed, the voltage on RESET IN
goes to zero, initiating a reset. Similar to the MAX6746/
MAX6747 manual reset, reset remains asserted while
the voltage at RESET IN is zero and for the reset time-
out period after the switch is opened.
MON_TH.
CC
and V
Manual Reset (MAX6746/MAX6747)
MON_TH
(see
t
RP
CC
Dual-Voltage Monitoring
voltage by connecting V
Figure
(MAX6750/MAX6751)
2). RESET is asserted
(Figure
CC
CC
3).
to