MAX6364LUT26-T Maxim Integrated, MAX6364LUT26-T Datasheet - Page 6

• Manufacturer Part Number: MAX6364LUT26-T
• Description: Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX6361, MAX6362, MAX6363, MAX6364r

Specifications of MAX6364LUT26-T

• Number Of Voltages Monitored: 1
• Monitored Voltage: 2.5 V, 3 V, 3.3 V, 5 V
• Undervoltage Threshold: 2.55 V
• Overvoltage Threshold: 2.7 V
• Output Type: Active Low, Push-Pull
• Manual Reset: Not Resettable
• Watchdog: No Watchdog
• Battery Backup Switching: Backup
• Power-up Reset Delay (typ): 280 ms
• Supply Voltage - Max: 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOT-23
• Chip Enable Signals: No
• Maximum Power Dissipation: 696 mW
• Minimum Operating Temperature: - 40 C
• Power Fail Detection: No
• Supply Current (typ): 15 uA
• Supply Voltage - Min: 0 V

The Typical Operating Circuit shows a typical connection
for the MAX6361–MAX6364 family. OUT powers the stat-
ic random-access memory (SRAM). OUT is internally
connected to V
old, or to the greater of V
than the reset threshold. OUT can supply up to 150mA
from V
(MAX6363) output is low. When V
an internal MOSFET connects the backup battery to
OUT. The on-resistance of the MOSFET is a function of
backup-battery voltage and is shown in the Battery to
Out On-Resistance vs. Temperature graph in the Typical
Operating Characteristics section.
In a brownout or power failure, it may be necessary to
preserve the contents of the RAM. With a backup bat-
tery installed at BATT, the MAX6361–MAX6364 auto-
matically switch the RAM to backup power when V
falls. The MAX6363 has a BATT ON output that goes
high when in battery-backup mode. These devices
require two conditions before switching to battery-
backup mode:
1) V
2) V
Table 1 lists the status of the inputs and outputs in bat-
tery-backup mode. The device will not power up if the
only voltage source is on BATT. OUT will only power up
from V
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 MAX6361, a logic
low on MR asserts reset. Reset remains asserted while
MR is low, and for a minimum of 150ms (t
returns high. MR has an internal 20kΩ pull-up resistor to
V
els or with open-drain/collector outputs. Connect a nor-
mally open momentary switch from MR to GND to create
a manual reset function; external debounce circuitry is
not required. If MR is driven from long cables or the
device is used in a noisy environment, connect a 0.1µF
capacitor from MR to GND to provide additional noise
immunity.
The watchdog monitors µP activity through the input
WDI. If the µP becomes inactive, the reset output is
asserted in pulses. To use the watchdog function, con-
nect WDI to a bus line or µP I/O line. A change of state
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup
6
CC
_______________________________________________________________________________________
. This input can be driven with TTL/CMOS logic lev-
CC
CC
CC
CC
must be below the reset threshold.
must be below V
Manual Reset Input (MAX6361 Only)
. When V
at startup.
Watchdog Input (MAX6362 Only)
CC
CC
if V
Backup-Battery Switchover
CC
is higher than V
Detailed Description
is greater than the reset thresh-
BATT
CC
or V
.
CC
BATT
is lower than V
BATT
when V
, the BATT ON
RP
CC
) after it
is less
BATT
CC
,
(high to low or low to high) within the watchdog timeout
period (t
the watchdog timer. If WDI remains high or low for longer
than the watchdog timeout period, the internal watchdog
timer runs out and a reset pulse is triggered for the reset
timeout period (t
whenever reset asserts or the WDI sees a rising or falling
edge within the watchdog timeout period. If WDI remains
in a high or low state for an extended period of time, a
reset pulse asserts after every watchdog timeout period
(t
RESET IN is compared to an internal 1.235V reference.
If the voltage at RESET IN is less than 1.235V, reset is
asserted. The RESET IN comparator may be used as
an undervoltage detector to signal a failing power sup-
ply. It can also be used as a secondary power-supply
reset monitor.
To program the reset threshold (V
power supply, use the following equation (see Typical
Operating Circuit ):
where V
choose a value for R2 and calculate R1:
Since the input current at RESET IN is 25nA (max), large
values (up to 1MΩ) can be used for R2 with no signifi-
cant loss in accuracy. For example, in the Typical
Table 1. Input and Output Status in
Battery-Backup Mode
WD
MR, RESET IN,
RESET/RESET
) (Figure 1).
BATT ON
BATT
OUT
V
WDI
PIN
REF
CC
WD
) with a 100ns minimum pulse width clears
= 1.235V. To simplify the resistor selection,
R
1
V
=
RP
RTH
). The internal watchdog timer clears
Disconnected from OUT
Connected to BATT
Connected to OUT. Current drawn from
the battery is less than 1µA (at V
2.8V, excluding I
Asserted
High state
Inputs ignored
R
2
=
[
V
(
Reset In (MAX6364 Only)
V
REF
RTH
⎛
⎜
⎝
/
R
R
V
2
REF
1
STATUS
OUT
RTH
+
)
1
⎞
⎟
⎠
) when V
−
) of the secondary
1
]
CC
BATT
= 0.
=