MAX820TCPE Maxim Integrated, MAX820TCPE Datasheet - Page 13

• Manufacturer Part Number: MAX820TCPE
• Description: Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX792, MAX792L, MAX792M, MAX792R, MAX792S, MAX792T, MAX820, MAX820L, MAX820M, MAX820R, MAX820S, MAX820Tr

Specifications of MAX820TCPE

• Number Of Voltages Monitored: 1
• Monitored Voltage: 2.75 V to 5.5 V
• Undervoltage Threshold: 3 V
• Overvoltage Threshold: 3.15 V
• Output Type: Active High, Active Low, Push-Pull
• Manual Reset: Resettable
• Watchdog: Watchdog
• Battery Backup Switching: No 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): 150 uA
• Supply Voltage - Min: 2.75 V

The MAX792/MAX820 provide internal gating of chip-
enable (CE) signals, which prevents erroneous data
from corrupting CMOS RAM in the event of an under-
voltage condition. The MAX792/MAX820 use a series
transmission gate from CE IN to CE OUT (Figure 1).
During normal operation (reset not asserted), the CE
transmission gate is enabled and passes all CE transi-
tions. When reset is asserted, this path becomes dis-
abled, preventing erroneous data from corrupting the
CMOS RAM. The 10ns max CE propagation delay from
CE IN to CE OUT enables the MAX792/MAX820 to be
used with most µPs. If CE IN is low when reset asserts,
CE OUT remains low for a short period to permit com-
pletion of the current write cycle.
The CE transmission gate is disabled and CE IN is high
impedance (disabled mode) while reset is asserted.
During a power-down sequence when V
reset threshold, the CE transmission gate disables and
CE IN immediately becomes high impedance if the volt-
age at CE IN is high. If CE IN is low when reset is assert-
ed, the CE transmission gate will disable at the moment
CE IN goes high or 15µs after reset is asserted,
whichever occurs first (Figure 9). This permits the cur-
rent write cycle to complete during power-down.
During a power-up sequence, the CE transmission gate
remains disabled and CE IN remains high impedance
regardless of CE IN activity, until reset is deasserted fol-
lowing the reset timeout period.
While disabled, CE IN is high impedance. When the CE
transmission gate is enabled, the impedance of CE IN
will appear as a 75Ω (V
the load at CE OUT.
The propagation delay through the CE transmission
gate depends on V
drive connected to CE IN, and the loading on CE OUT
(see the Chip-Enable Propagation Delay vs. CE OUT
Load Capacitance graph in the Typical Operating
Characteristics). The CE propagation delay is produc-
tion tested from the 50% point on CE IN to the 50%
point on CE OUT using a 50Ω driver and 50pF of load
capacitance (Figure 10). For minimum propagation
delay, minimize the capacitive load at CE OUT, and use
a low-output-impedance driver.
______________________________________________________________________________________
CC,
Chip-Enable Signal Gating
CC
the source impedance of the
= 5V) resistor in series with
Chip-Enable Input
Microprocessor and Nonvolatile
CC
passes the
Memory Supervisory Circuits
When the CE transmission gate is enabled, the imped-
ance of CE OUT is equivalent to 75Ω in series with the
source driving CE IN. In the disabled mode, the 75Ω
transmission gate is off and an active pull-up connects
from CE OUT to V
transmission gate is enabled.
Connect a 0.1µF ceramic capacitor from V
as close to the device pins as possible. This reduces
the probability of resets due to high-frequency power-
supply transients. In a high-noise environment, addi-
tional bypass capacitance from V
required. If long leads connect to the chip inputs,
ensure that these lines are free from ringing, etc., which
would forward bias the chip’s protection diodes.
Figure 9. Reset and Chip-Enable Timing
Figure 10. CE Propagation Delay Test Circuit
THRESHOLD
CE OUT
RESET
RESET
RESET
CE IN
50Ω DRIVER
V
CC
Applications Information
CC
14
. This source turns off when the
CE IN
MAX792
MAX820
GND
+5V
V
CC
3
12
CE OUT
15µs
70µs
CC
Chip-Enable Output
13
to ground may be
C
LOAD
CC
70µs
to GND,
13