MAX6414UK26T Datasheet, PDF (6/12 Pages) Maxim Integrated Products – Low-Power, Single/Dual-Voltage uP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay

MAX6412–MAX6420
Low-Power, Single/Dual-Voltage µP Reset Circuits
with Capacitor-Adjustable Reset Timeout Delay
Use the following formula to calculate the externally
monitored voltage (V_{MON_TH}):
V_{MON_TH} = V_RST  (R1 + R2)/R2
where V_{MON_TH} is the desired reset threshold voltage
and V_RST is the reset input threshold (1.26V). Resistors
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 (1MΩ, for example)
and calculate R1 based on the desired monitored volt-
age, using the following formula:
R1 = R2 x (V_{MON_TH}/V_RST - 1) (Ω)
Manual Reset Input
(MAX6412/MAX6413/MAX6414)
Many µP-based products require manual reset capabil-
ity, allowing the operator, a technician, or external logic
circuitry to initiate a reset. A logic low on MR asserts
reset. Reset remains asserted while MR is low and for
the reset timeout period after MR returns high.
The MR has an internal 20kΩ pullup resistor so it can
be left open if not used. Connect a normally open
momentary switch from MR to ground to create a man-
ual reset function (external debounce circuitry is not
required for long reset timeout periods).
A manual reset option can easily be implemented with the
MAX6415–MAX6420 by connecting a normally open
momentary switch in parallel with R2 (Figure 2). When the
switch is closed, the voltage on RESET IN goes to zero,
initiating a reset. Similar to the MAX6412/MAX6413/
MAX6414 manual reset, reset remains asserted while the
switch is closed and for the reset timeout period after the
switch is opened.
V_{MON_TH}
V_CC
R1
RESET IN
V_CC
R2
MAX6415–
MAX6420
GND
SRT
Figure 2. Adding an External Manual Reset Function to the
MAX6415–MAX6420
Monitoring Voltages Other than V_CC
(MAX6415/MAX6416/MAX6417)
The MAX6415/MAX6416/MAX6417 contain an adjustable
reset threshold input. These devices can be used to
monitor voltages other than V_CC. Calculate V_{MON_TH} as
shown in the Reset Threshold section. (See Figure 3.)
V_{MON_TH}
V_CC
R1
RESET IN
V_CC
R2
MAX6415
MAX6416
GND _MAX6417
SRT
V_{MON_TH} = 1.26 x (R1 + R2)/R2
R1
RESET IN
V_CC
R2
MAX6415
MAX6416
GND _MAX6417
SRT
Figure 1. Calculating the Monitored Threshold Voltage (V_{MON_TH})
6
Figure 3. Monitoring External Voltages
Maxim Integrated