MAX791EJE(1995) 查看數據表（PDF） - Maxim Integrated
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MAX791EJE Datasheet PDF : 20 Pages
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Microprocessor Supervisory Circuit
+5V
1N4148
0.47F
3
VCC
1
VBATT
2
VOUT
MAX791
GND
4
Figure 12. SuperCap or MaxCap on VBATT
Rp*
VOUT
CE IN
CE OUT
MAX791
GND
CE
RAM 1
CE
CE
RAM 2
CE
CE
RAM 3
CE
CE
RAM 4
CE
*MAXIMUM Rp VALUE DEPENDS ON
THE NUMBER OF RAMS.
MINIMUM Rp VALUE IS 1kΩ
ACTIVE-HIGH CE
LINES FROM LOGIC
Figure 13. Alternate CE Gating
Low-Battery Monitor
The MAX791 low-battery voltage function monitors
VBATT. Low-battery detection of 2.0V ±0.15V is moni-
tored only during the reset-timeout period (200ms) that
occurs either after a normal power-up sequence or
after the MR reset input has been returned to its high
state. If the battery voltage is below 2.0V, the second
CE pulse is inhibited after reset timeout. If the battery
voltage is above 2.0V, all CE pulses are allowed
through the CE gate after the reset timeout period. To
use this function, after the 200ms reset delay, write 00
(HEX) to a location using the first CE pulse, and write
FF (HEX) to the same location using the second CE
pulse following RESET going inactive on power-up. The
contents of the memory then indicates a good battery
(FF) or a low battery (00) (Figure 11).
__________Applications Information
The MAX791 is not short-circuit protected. Shorting
VOUT to ground, other than power-up transients such
as charging a decoupling capacitor, destroys the
device.
All open-circuit outputs swing between VOUT and GND
rather than VCC and GND.
If long leads connect to the chip inputs, ensure that
these lines are free from ringing and other conditions
that would forward bias the chip’s protection diodes.
There are three distinct modes of operation:
1) Normal operating mode with all circuitry powered
up. Typical supply current from VCC is 60µA, while
only leakage currents flow from the battery.
2) Battery-backup mode where VCC is typically within
0.7V below VBATT. All circuitry is powered up and
the supply current from the battery is typically less
than 60µA.
3) Battery-backup mode where VCC is less than
VBATT by at least 0.7V. VBATT supply current is
than 1µA max.
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