ADM8696(Rev0) Просмотр технического описания (PDF) - Analog Devices
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ADM8696 Datasheet PDF : 12 Pages
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ADM8696/ADM8697
CE Gating and RAM Write Protection (ADM8697)
The ADM8697 contains memory protection circuitry that
ensures the integrity of data in memory by preventing write
operations when LLIN is below the threshold voltage. When
LLIN is greater than 1.3 V, CEOUT is a buffered replica of CEIN,
with a 2 ns propagation delay. When LLIN falls below the 1.3 V
threshold, an internal gate forces CEOUT high, independent of
CEIN.
CEOUT typically drives the CE, CS or Write input of battery
backed up CMOS RAM. This ensures the integrity of the data
in memory by preventing write operations when VCC is at an in-
valid level.
can be chosen such that the voltage at PFI falls below 1.3 V
several milliseconds before the +5 V power supply falls below
the reset threshold. PFO is normally used to interrupt the
microprocessor so that data can be stored in RAM and the shut-
down procedure executed before power is lost.
INPUT
POWER
R1
R2
POWER
FAIL
INPUT
ADM869x
1.3V
PFO
POWER
FAIL
OUTPUT
ADM8697
CEIN
LLIN LOW = 0
LLIN OK = 1
CEOUT
Figure 5. Chip Enable Gating
V2
V2
LLIN
V1
V1
RESET
t1
t1
LOW LINE
CEIN
CEOUT
t1 = RESET TIME
V1 = RESET VOLTAGE THRESHOLD LOW
V2 = RESET VOLTAGE THRESHOLD HIGH
HYSTERESIS = V2–V1
Figure 6. Chip Enable Timing
Power Fail Warning Comparator
An additional comparator is provided for early warning of fail-
ure in the microprocessor’s power supply. The Power Fail Input
(PFI) is compared to an internal +1.3 V reference. The Power
Fail Output (PFO) goes low when the voltage at PFI is less than
1.3 V. Typically PFI is driven by an external voltage divider
which senses either the unregulated dc input to the system’s 5 V
regulator or the regulated 5 V output. The voltage divider ratio
Figure 7. Power Fail Comparator
Table II. Input and Output Status In Battery Backup Mode
Signal
Status
VOUT
RESET
RESET
LOW LINE
BATT ON
WDI
WDO
PFI
PFO
CEIN
CEOUT
OSC IN
OSC SEL
(ADM8696) VOUT is connected to VBATT via an
internal PMOS switch.
Logic low.
Logic high. The open circuit output voltage is
equal to VOUT.
Logic low.
(ADM8696) Logic high. The open circuit volt-
age is equal to VOUT.
WDI is ignored. It is internally disconnected
from the internal pull-up resistor and does not
source or sink current as long as its input voltage
is between GND and VOUT. The input voltage
does not affect supply current.
Logic high. The open circuit voltage is equal to
VOUT.
The Power Fail Comparator is turned off and
has no effect on the Power Fail Output.
Logic low.
CEIN is ignored. It is internally disconnected
from its internal pull-up and does not source or
sink current as long as its input voltage is be-
tween GND and VOUT. The input voltage does
not affect supply current.
Logic high. The open circuit voltage is equal to
VOUT.
OSC IN is ignored.
OSC SEL is ignored.
REV. 0
–7–
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