Rainbow Electronics MAX16024 - Manual (Page 12)

MAX16023/MAX16024
Manual-Reset Input
(MAX16023/MAX16024)
Many µP-based products require manual-reset capabili-
ty, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. For the MAX16023/
MAX16024, a logic-low on MR asserts RESET. RESET
remains asserted while MR is low. When MR goes high,
RESET deasserts after a minimum of 145ms (t
RP ). MR
has an internal 30k
Ω pullup resistor to V
CC . MR can be
driven with TTL/CMOS logic levels or with open-
drain/collector outputs. Connect a normally open
momentary switch from MR to GND to create a manual-
reset function; external debounce circuitry is not
required. If MR is driven from a long cable or the device
is used in a noisy environment, connect a 0.1µF capaci-
tor from MR to GND to provide additional noise immunity.
Battery-On Indicator (MAX16024)
The MAX16024’s BATT ON output goes high when in
battery-backup mode. Use BATT ON to indicate bat-
tery-switchover status.
Battery Freshness Seal
The MAX16023/MAX16024 battery freshness seal dis-
connects the backup battery from internal circuitry and
OUT until V
CC is applied. This ensures the backup bat-
tery connected to BATT is fresh when the final product
is used for the first time.
The internal freshness seal latch prevents BATT from
powering OUT until V
CC has come up for the first time,
setting the latch. When V CC subsequently turns off,
BATT begins to power OUT.
To reenable the freshness seal (MAX16023/
MAX16024):
1) Connect a battery to BATT.
2) Bring V CC to 0.
3) Drive MR higher than V
BATT
+ 1.2V for at least 3µs.
4) Pull OUT to 0.
Reset Output (MAX16023/MAX16024)
A µP’s reset input starts the µP in a known state. The
MAX16023/MAX16024 µP supervisory circuits assert a
reset to prevent code-execution errors during power-
up, power-down, and brownout conditions. RESET
asserts when V
CC is below the reset threshold and
remains low for at least 145ms (t RP ) after V CC rises
above the reset threshold. RESET also asserts when
MR is low. RESET is available in both push-pull and
open-drain configurations.
Power-Fail Comparator (MAX16023)
The MAX16023 offers an additional undervoltage com-
parator. The output PFO goes low when the voltage at
PFI falls below its V
PFT
threshold. Common uses for the
power-fail comparator include monitoring the input of the
power supply (such as a battery) before any voltage reg-
ulation to provide an early power-fail warning, so soft-
ware can conduct an orderly system shutdown. The
power-fail comparator has a typical input hysteresis of
V
PFT-HYS
and is powered from OUT, making it indepen-
dent of the reset circuit. Connect PFI to GND, if not used.
Regulator Output
Fixed output voltages of 1.2V, 1.8V, 2.5V, 3.0V, and
3.3V are available for all devices. The regulator output
delivers up to 100mA of load current.
The MAX16024 is available with both fixed and
adjustable output-voltage options. Use an external
resistive divider network connected between OUT, SET,
and GND (Figure 2) to set the adjustable output voltage
from 1.8V to 5.25V. Connect SET to GND for parts with
fixed output voltage option.
Battery-Backup Circuits with
Regulated Output Voltage
12 ______________________________________________________________________________________
MAX16024
0.1 μF
1.53 TO 5.5V
GND
V CC
RESET TO μP
R1
R2
SET
10 μF
1.8V TO 5.25V
V OUT = V SET (1 + R1/R2)
V SET = 1.2V
OUT
Figure 2. Setting the Adjustable Output Voltage (MAX16024
Only)