MAX807N Maxim Integrated Products, MAX807N Datasheet - Page 8

• Manufacturer Part Number: MAX807N
• Description: Full-Featured P Supervisory Circuit with 1.5eset Accuracy
• Manufacturer: Maxim Integrated Products

Full-Featured µP Supervisory Circuit with
±1.5% Reset Accuracy
The MAX807 microprocessor (µP) supervisory circuit
provides power-supply monitoring, backup-battery
switchover, and program execution watchdog functions
in µP systems (Figure 1). Use of BiCMOS technology
results in an improved 1.5% reset-threshold precision,
while keeping supply currents typically below 70µA.
The MAX807 is intended for battery-powered applica-
tions that require high reset-threshold precision, allow-
ing a wide power-supply operating range while
preventing the system from operating below its speci-
fied voltage range.
Figure 1. Block Diagram
8
_______________Detailed Description
_______________________________________________________________________________________
CE IN
BATT
GND
V
PFI
CC
2.275V
BATTERY-BACKUP
COMPARATOR
RESET
COMPARATOR
LOW-LINE
COMPARATOR
BATTERY-OK
COMPARATOR
POWER-FAIL
COMPARATOR
MAX807
OSCILLATOR
The MAX807’s RESET output ensures that the µP pow-
ers up in a known state, and prevents code execution
errors during power-down and brownout conditions. It
accomplishes this by resetting the µP, terminating pro-
gram execution when V
old or MR is pulled low. Each time RESET is asserted it
stays low for the 200ms reset timeout period, which is
set by an internal timer to ensure the µP has adequate
time to return to an initial state. Any time V
below the reset threshold before the reset timeout peri-
od is completed, the internal timer restarts. The watch-
dog timer can also initiate a reset if WDO is connected
to MR. See the Watchdog Input section.
P
N
WATCHDOG
TRANSITION
DETECTOR
MACHINE
STATE
OF V
THE HIGHER
CC
V
OR V
CC
RESET and RESET Outputs
P
50k
BATT
CC
P
N
dips below the reset thresh-
OUT
BATT ON
LOW LINE
BATT OK
PFO
WDI
MR
RESET
RESET
WDO
CE OUT
CC
goes