MXD1210C/D 데이터 시트보기 (PDF) - Maxim Integrated

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MXD1210C/D

Nonvolatile RAM Controller

Maxim Integrated 

Nonvolatile RAM Controller

Detailed Description

Main Functions

The MXD1210 executes five main functions to perform

reliable RAM operation and battery backup (see the

Typical Operating Circuit and Figure 1):

1) RAM Power-Supply Switch: The switch directs

power to the RAM from the incoming supply or

from the selected battery, whichever is at the

greater voltage. The switch control uses the same

criterion to direct power to MXD1210 internal cir-

cuitry.

2) Power-Failure Detection: The write-protection

function is enabled when a power failure is

detected. The power-failure detection range

depends on the state of the TOL pin as follows:

CONDITION

TOL = GND

TOL = VCCO

VCCTP RANGE (V)

4.75 to 4.50

4.50 to 4.25

Power-failure detection is independent of the bat-

tery-backup function and precedes it sequentially

as the power-supply voltage drops during a typi-

cal power failure.

3) Write Protection: This holds the chip-enable out-

put (CEO) to within 0.2V of VCCI or of the selected

battery, whichever is greater. If the chip-enable

input (CE) is low (active) when power failure is

detected, then CEO is held low until CE is brought

high, at which time CEO is gated high for the

duration of the power failure. The preceding

sequence completes the current RD/WR cycle,

preventing data corruption if the RAM access is a

WR cycle.

4) Battery Redundancy: A second battery is option-

al. When two batteries are connected, the

stronger battery is selected to provide RAM back-

up and to power the MXD1210. The battery-selec-

tion circuitry remains active while in the

battery-backup mode, selecting the stronger bat-

tery and isolating the weaker one. The battery-

selection activity is transparent to the user and

the system. If only one battery is connected, the

second battery input should be grounded.

5) Battery-Status Warning: This notifies the system

when the stronger of the two batteries measures ≤

2.0V. Each time the MXD1210 is repowered (VCCI

> VCCTP) after detecting a power failure, the bat-

tery voltage is measured. If the battery in use is

low, following the MXD1210 recovery period, the

device issues a warning to the system by inhibit-

ing the second memory cycle. The sequence is

as follows:

First access: read memory location n, loc(n) = x

Second access: write memory location n,

loc(n) = complement (x)

Third access: read memory location n, loc(n) = ?

If the third access (read) is complement (x), then the

battery is good; otherwise the battery is not good.

Return to loc(n) = x following the test sequence.

Freshness-Seal Mode

The freshness-seal mode relates to battery longevity

during storage rather than directly to battery backup.

This mode is activated when the first battery is con-

nected, and is defeated when the voltage at VCCI first

exceeds VCCTP. In the freshness-seal mode, both bat-

teries are isolated from the system; that is, no current is

drained from either battery, and the RAM is not pow-

ered by either battery. This means that batteries can be

installed and the system can be held in inventory with-

out battery discharge. The positive edge rate at

VBATT1 and VBATT2 should exceed 0.1V/µs. The bat-

teries will maintain their full shelf life while installed in

the system.

Battery Backup

The Typical Operating Circuit shows the MXD1210 con-

nected to write-protect the RAM when VCC is less than

4.75V, and to provide battery backup to the supply.

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