LTC692CS8 datasheet(10/16 Pages) LINER

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LTC692/LTC693

VCC

CE IN

VOUT = VBATT

CE OUT

VOUT = VBATT

V1 = RESET VOLTAGE THRESHOLD

V2 = RESET VOLTAGE THRESHOLD +

RESET THRESHOLD HYSTERESIS

LTC692/3 • F05

Memory Protection

The LTC693 includes memory protection circuitry which

ensures the integrity of the data in memory by preventing

write operations when VCC is at an invalid level. Two

additional pins, CE IN and CE OUT, control the Chip Enable

or Write inputs of CMOS RAM. When VCC is 5V, CE OUT

follows CE IN with a typical propagation delay of 20ns.

When VCC falls below the reset voltage threshold or VBATT,

CE OUT is forced high, independent of CE IN. CE OUT is an

APPLICATI

I FOR ATIO

If battery connections are made through long wires, a 10

Ω

to 100

Ω series resistor and a 0.1µF capacitor are recom-

mended to prevent any overshoot beyond VCC due to the

lead inductance (Figure 4).

alternative signal to drive the CE, CS, or Write input of

battery backed up CMOS RAM. CE OUT can also be used

to drive the Store or Write input of an EEPROM, EAROM or

NOVRAM to achieve similar protection. Figure 5 shows the

timing diagram of CE IN and CE OUT.

CE IN can be derived from the microprocessor's address

decoder output. Figure 6 shows a typical nonvolatile

CMOS RAM application.

Memory protection can also be achieved with the LTC692

by using RESET as shown in Figure 7.

SIGNAL

STATUS

VCC

C2 monitors VCC for active switchover.

VOUT

VOUT is connected to VBATT through an internal PMOS switch.

VBATT

The supply current is 1

µA maximum.

BATT ON

Logic high. The open-circuit output voltage is equal to VOUT.

PFI

Power Failure Input is ignored.

PFO

Logic low

RESET

Logic low

RESET

Logic high. The open-circuit output voltage is equal to VOUT.

LOW LINE Logic low

WDI

Watchdog Input is ignored.

WDO

Logic high. The open-circuit output voltage is equal to VOUT.

CE IN

Chip Enable Input is ignored.

CE OUT

Logic high. The open-circuit output voltage is equal to VOUT.

OSC IN

OSC IN is ignored.

OSC SEL

OSC SEL is ignored.

Table 1. Input and Output Status in Battery Backup Mode

3.9M

0.1µF

VBATT

LTC692

LTC693

GND

LTC692/3 • F04

Ω

Figure 4. 10

Ω/0.1µF combination eliminates inductive

overshoot and prevents spurious resets during battery

replacement.

Table 1 shows the state of each pin during battery backup.

When the battery switchover section is not used, connect

VBATT to GND and VOUT to VCC.

Figure 5. Timing Diagram for CE IN and CE OUT

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