MAX16039 Maxim Integrated Products, MAX16039 Datasheet - Page 10

• Manufacturer Part Number: MAX16039
• Description: (MAX16033 - MAX16040) Low-Power Battery Backup Circuits
• Manufacturer: Maxim Integrated Products

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Table 1. Input and Output Status in
Battery-Backup Mode
Low-Power Battery Backup
Circuits in Small µDFN Packages
To preserve the contents of the RAM in a brownout or
power failure, the MAX16033–MAX16040 automatically
switch to back up the battery installed at BATT when
the following two conditions are met:
1) V
2) V
Table 1 lists the status of the inputs and outputs in bat-
tery-backup mode. The devices do not power-up if the
only voltage source is V
V
Many µP-based products require manual-reset capabil-
ity, allowing the user or external logic circuitry to initiate
a reset. For the MAX16033/MAX16037, a logic-low on
MR asserts RESET. RESET remains asserted while MR
is low and for a minimum of 140ms (t
high. MR has an internal 20kΩ (min) pullup resistor to
10
CEIN, and WDI
CC
MR, RESETIN,
BATTON
CC
CC
CEOUT
RESET
______________________________________________________________________________________
at startup.
BATT
OUT
PFO
V
PIN
CC
falls below the reset threshold voltage.
is below V
Disconnected from OUT
Connected to BATT
Connected to OUT. Current drawn from the
battery is less than 1µA (at V
excluding I
Asserted
High state
Inputs ignored
Connected to OUT
Asserted
BATT
(MAX16033/MAX16037 Only)
Backup Battery Switchover
.
BATT
OUT
. OUT only powers up from
) when V
Manual-Reset Input
STATUS
CC
RP
= 0V.
) after it returns
BATT
= 2.8V,
V
outputs or with open-drain/collector outputs. Connect a
normally-open momentary switch from MR to GND to
create a manual-reset function; external debounce cir-
cuitry is not required. When driving MR from long
cables or when using the device in a noisy environ-
ment, connect a 0.1µF capacitor from MR to GND to
provide additional noise immunity.
The watchdog monitors µP activity through the watch-
dog input (WDI). RESET asserts when the µP fails to
toggle WDI. Connect WDI to a bus line or µP I/O line. A
change of state (high to low, low to high, or a minimum
100ns pulse) resets the watchdog timer. If WDI remains
high or low for longer than the watchdog timeout period
(t
a reset pulse for the reset timeout period (t
internal watchdog timer clears whenever reset is
asserted or whenever WDI sees a rising or falling edge.
If WDI remains in either a high or low state, a reset
pulse periodically asserts after every watchdog timeout
period (t
Figure 2. MAX16034/MAX16038 Watchdog Timeout Period and
Reset Active Time
WD
CC
t
t
. This input can be driven from TTL/CMOS logic
WD
RP
), the internal watchdog timer runs out and triggers
RESET
= RESET TIMEOUT PERIOD
WDI
= WATCHDOG TIMEOUT PERIOD
WD
); see Figure 2.
(MAX16034/MAX16038 Only)
t
WD
t
RP
Watchdog Input
t
WD
t
RP
RP
). The