Rainbow Electronics MAX16021 - Manual (Page 10)

MAX16016/MAX16020/MAX16021
Low-Power µP Supervisory Circuits with
Battery-Backup Circuit and Chip-Enable Gating
10 ______________________________________________________________________________________
Pin Description—MAX16020/MAX16021
PIN
MAX16020 MAX16021
NAME FUNCTION
1 1 BATT
Backup Battery Input. If V CC falls below its reset threshold, and if V BATT > V CC , OUT
connects to BATT. If V
CC
rises above 1.01 x V
BATT
, OUT connects to V
CC
. Bypass BATT to
GND with a 0.1µF capacitor.
2 2 MR
Active-Low Manual Reset Input. RESET asserts when MR is pulled low. RESET remains low
for the duration of reset timeout period after MR transitions from low to high. Connect MR to
OUT or leave unconnected if not used. MR is internally connected to OUT through a 30k
Ω
pullup resistor.
3 3 PFI
Power-Fail Comparator Input. Connect PFI to a resistive divider to set the desired PFI
threshold. The PFI input is referenced to an internal threshold V
PFT , V PFI-HYS internal
hysteresis provides noise immunity. The power-fail comparator is powered from OUT.
4 4 WDI
Watchdog Timer Input. If WDI remains high or low for longer than the watchdog timeout
period (t
WD ), the internal watchdog timer runs out and asserts WDO. The internal watchdog
clears when reset asserts or whenever WDI sees a rising or falling edge. To disable the
watchdog feature, leave WDI unconnected or three-state the driver connected to WDI.
5 5 LL
Active-Low Low-Line Output. LL goes low when V CC falls to 2.5% above the reset threshold
(Table 2). LL provides an early warning of V
CC
failure before reset asserts. Use this output
to generate a nonmaskable interrupt (NMI) to initiate an orderly shutdown routine when
V
CC is falling.
6 — BATT_TEST
Open-Drain Battery-Test Output. Pulses low for 1.3s every 24 hours during the battery
voltage test. If V
BATT < 2.6V, BATTOK deasserts low. See Figure 6 for providing additional
load during the battery test.
— 6 RESET
Active-High Reset Output. RESET asserts when V CC falls below the reset threshold or when
MR asserts and stays asserted for the reset timeout period after V
CC rises above the reset
threshold and MR deasserts.
7 7 BATTOK
Battery-OK Output. BATTOK goes low when the battery voltage falls below the BATTOK
threshold (BATTOK is low when in battery-backup mode).
8 8 BATTON Active-High Battery-On Output. BATTON goes high when in battery-backup mode.