MAX706R MAXIM [Maxim Integrated Products], MAX706R Datasheet - Page 7

• Manufacturer Part Number: MAX706R
• Description: +3V Voltage Monitoring, Low-Cost uP Supervisory Circuits
• Manufacturer: MAXIM [Maxim Integrated Products]

A microprocessor’s (µP’s) reset input starts in a known
state. When the µP is in an unknown state, it should be
held in reset. The MAX706P/R/S/T and the MAX706AP/
AR/AS/AT assert reset when V
code execution errors during power-up, power-down,
or brownout conditions.
On power-up once V
teed to be logic-low and RESET is guaranteed to be
logic-high. As V
asserted. Once V
internal timer causes RESET and RESET to be
deasserted after a time equal to the reset pulse width,
which is typically 200ms (Figure 3).
If a power-fail or brownout condition occurs (i.e., V
drops below the reset threshold), RESET and RESET
are asserted. As long as V
threshold, the internal timer is continually reset, causing
the RESET and RESET outputs to remain asserted.
Thus, a brownout condition that interrupts a previously
initiated reset pulse causes an additional 200ms delay
from the time the latest interruption occurred. On
power-down once V
Figure 1. MAX706_ Functional Diagram
( ) ARE FOR MAX706P/AP.
V
WDI
MR
PFI
CC
6
1
2
4
V
CC
TRANSITION
WATCHDOG
DETECTOR
70µA
1.25V
2.63V MAX706P/R
2.93V MAX706S
3.08V MAX706T
CC
CC
_______________________________________________________________________________________
CC
RESET and
rises, RESET and RESET remain
CC
exceeds the reset threshold, the
MAX706AP/AR/AS/AT
drops below the reset threshold,
reaches 1V, RESET is guaran-
MAX706P/R/S/T
3
+3V Voltage Monitoring, Low-Cost µP
TIMEBASE FOR
GENERATOR
WATCHDOG
WATCHDOG
GND
CC
RESET AND
RESET
TIMER
remains below the reset
CC
RESET Outputs
is low, preventing
8
7
5
PFO
WDO
RESET
(RESET)
CC
RESET and RESET are guaranteed to be asserted for
V
The MAX706P/MAX706AP provide a RESET signal, and
the MAX706R/S/T and MAX706AR/AS/AT provide a
RESET signal. The MAX708R/S/T provide both RESET
and RESET.
The MAX706P/R/S/T and the MAX706AP/AR/AS/AT
watchdog circuit monitor the µP’s activity. If the µP
does not toggle the watchdog input (WDI) within 1.6s,
the watchdog output (WDO) goes low (Figure 4). If the
reset signal is asserted, the watchdog timer will be
reset to zero and disabled. As soon as reset is
released, the timer starts counting. WDI can detect puls-
es as narrow as 100ns with a 2.7V supply and 50ns with a
4.5V supply. The watchdog timer for the MAX706P/R/S/T
cannot be disabled. The watchdog timer for the
MAX706AP/AR/AS/AT operates similarly to the
MAX706P/R/S/T. However, the watchdog timer for the
MAX706AP/AR/AS/AT disables when the WDI input is
left open or connected to a tri-state output in its high-
impedance state and with a leakage current of less
than 600nA. The watchdog timer can be disabled any-
time, provided WDO is not asserted.
Figure 2. MAX708_ Functional Diagram
V
MR
CC
PFI
CC
≥ 1V.
1
2
4
Supervisory Circuits
V
CC
70µA
1.25V
2.63V MAX708R
2.93V MAX708S
3.08V MAX708T
3
GENERATOR
GND
RESET
MAX708R/S/T
Watchdog Timer
8
7
5
PFO
RESET
RESET
7