MAX807NCPE Maxim Integrated, MAX807NCPE Datasheet - Page 14

• Manufacturer Part Number: MAX807NCPE
• Description: Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX807L, MAX807M, MAX807Nr

Specifications of MAX807NCPE

• Number Of Voltages Monitored: 1
• Monitored Voltage: 4.575 V
• Undervoltage Threshold: 4.5 V
• Overvoltage Threshold: 4.65 V
• Output Type: Active High, Active Low
• Manual Reset: Resettable
• Watchdog: Watchdog
• Battery Backup Switching: Backup
• Power-up Reset Delay (typ): 280 ms
• Supply Voltage - Max: 5.5 V
• Maximum Operating Temperature: + 70 C
• Mounting Style: Through Hole
• Package / Case: PDIP N
• Chip Enable Signals: Yes
• Maximum Power Dissipation: 842 mW
• Minimum Operating Temperature: 0 C
• Power Fail Detection: Yes
• Supply Current (typ): 70 uA
• Supply Voltage - Min: 0 V

The BATT OK comparator monitors the backup battery
voltage, comparing it with a 2.265V reference (V
4V). BATT OK remains high as long as the backup bat-
tery voltage remains above 2.265V, signaling that the
backup battery has sufficient voltage to maintain the
memory of static RAM. When the battery voltage drops
below 2.265V, the BATT OK output drops low, signaling
that the backup battery needs to be changed.
The MAX807 is not short-circuit protected. Shorting
OUT to ground, other than power-up transients such as
charging a decoupling capacitor, may destroy the
device. If long leads connect to the IC’s inputs, ensure
that these lines are free from ringing and other condi-
tions that would forward bias the IC’s protection diodes.
There are two distinct modes of operation:
1) Normal Operating Mode, with all circuitry powered
2) Battery-Backup Mode, where V
BATT has the same operating voltage range as V
the battery-switchover threshold voltage is typically
V
V
Full-Featured µP Supervisory Circuit with
±1.5% Reset Accuracy
Figure 13. SuperCap or MaxCap on BATT
14
BATT
CC
up. Typical supply current from V
only leakage currents flow from the battery.
and V
ically less than 1µA.
______________________________________________________________________________________
is increasing. This hysteresis allows use of a
when V
RST
+5V
1N4148
0.47F
. The supply current from the battery is typ-
CC
Applications Information
is decreasing or V
MaxCaps with the MAX807
BATT
MAX807
GND
V
Using SuperCaps or
CC
BATT OK Output
OUT
CC
BATT
CC
is below V
is 70µA, while
+ 0.06V when
CC
CC
, and
BATT
≥
SuperCap (e.g., order of 0.47F) and a simple charging
circuit as a backup source (Figure 13). Since V
exceed V
there are no special precautions when using these µP
supervisors with a SuperCap.
Using memory devices with CE and CE inputs allows
the MAX807 CE loop to be bypassed. To do this, con-
nect CE IN to ground, pull up CE OUT to OUT, and
connect CE OUT to the CE input of each memory
device (Figure 14). The CE input of each part then con-
nects directly to the chip-select logic, which does not
have to be gated by the MAX807.
The power-fail comparator has a typical input hystere-
sis of 20mV. This is sufficient for most applications
where a power-supply line is being monitored through
an external voltage-divider (Figure 10).
Figure 15 shows how to add hysteresis to the power-fail
comparator. Select the ratio of R1 and R2 such that PFI
sees 2.265V when V
(V
an order of magnitude greater than R1 or R2. The cur-
rent through R1 and R2 should be at least 1µA to
ensure that the 25nA (max) PFI input current does not
shift the trip point. R3 should be larger than 10kΩ to
prevent it from loading down the PFO pin. Capacitor C1
adds additional noise rejection.
Figure 14. Alternate CE Gating
TRIP
*MAXIMUM Rp VALUE DEPENDS ON
THE NUMBER OF RAMs.
MINIMUM Rp VALUE IS 1kΩ.
). Resistor R3 adds hysteresis. It will typically be
CC
CE IN
while V
Alternative Chip-Enable Gating
MAX807
GND
OUT
CC
IN
CE OUT
Adding Hysteresis to the
Rp*
falls to the desired trip point
is above the reset threshold,
Power-Fail Comparator
ACTIVE-HIGH CE
LINES FROM LOGIC
CE
CE
CE
CE
CE
CE
CE
CE
BATT
RAM 1
RAM 2
RAM 3
RAM 4
can