DS1710 datasheet(2/14 Pages) DALLAS

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DS1710

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DESCRIPTION

The DS1710 is a low-power CMOS circuit which solves the application problems of converting CMOS

RAMS into nonvolatile memories. In addition the device has the ability to unconditionally write protect

blocks of memory so that inadvertent write cycles do not corrupt program and special data space. The

incoming power supply voltage at the VCCI input pin is constantly monitored for an out-of-tolerance

condition. When such a condition is detected, both the chip enable and write enable outputs are inhibited

to protect stored data. The battery inputs are used to supply VCCO with power when VCCI is less than the

battery input voltages. Special circuitry uses a low leakage CMOS process which affords precise voltage

detection at extremely low current consumption. By combining the DS1710 Partitioned NV Controller

chip with a CMOS memory and batteries, nonvolatile RAM operation can be achieved.

The DS1710 Partitioned NV Controller incorporates all the functions of the DS1610 with the additional

feature of either +3.0V or +5.0V operation. The DS1710 functions like the Dallas Semiconductor DS1210

NV controller when the ( DIS) disable pin is grounded and also incorporates the power-up auto sensing.

An internal pulldown resistor to ground on the DIS pin of the DS1710S allows it to retrofit into DS1210S

applications. When the DIS pin is grounded the address inputs AW - AZ and the write enable input WEI

are ignored. Also the power-fail output PFO and the write enable output WEO are tristated.

POWER-UP AUTO SENSING

VCCI will accept either +3.0V or +5.0V input. Selection of 3V operation is automatically invoked when

VCC rises and remains between VCCTP2 and VCCTP1 for tREC. 5V operation is automatically selected if VCC

rises and remains above both VCCTP2 and VCCTP1 for tREC. In either case, tREC is measured from the time

VCC first rises above VCCTP2. The DS1710 will not change modes until VCC falls below VCCTP2.

OPERATION - DISABLE PIN CONNECTED TO VCCO

The DS1710 performs five circuit functions required to battery-backup a RAM. First, a switch is provided

to direct power from the battery or the incoming power supply (VCCI) depending on which is greater. This

switch has a voltage drop of less than 0.2 volts. The second function provided by the DS1710 is power-

fail detection. The incoming supply (VCCI) is constantly monitored. When the supply goes out of

tolerance a precision comparator detects power failure and inhibits both the chip enable output ( CEO ) and

the write enable output ( WEO ). A third function of write protection is accomplished by holding both the

chip enable output CEO and write enable output WEO to within 0.2 volts of VCCO when VCCI is out of

tolerance. If CEI is low at the time that power-fail detection occurs the CEO signal is kept low until CEI

is brought high again. However, CEO is forced high after 1.5 µs regardless of the state of CEI . Similarly,

if WEI is low at the time that power-fail detection occurs, the WEO signal will remain low until WEI is

brought high or 1.5 µs elapses. The delay of write protection until the current memory cycle is complete

prevents corrupted data. Power-fail detection occurs in the range of 4.75 to 4.5 volts with the tolerance

pin TOL grounded and in 5-volt mode. If the tolerance pin is connected to VCCO while in 5-volt mode,

then power-fail detection occurs in the range of 4.5 volts to 4.25 volts. If in 3-volt mode, the power-fail

detection will occur in the range of 2.7 to 2.5 volts. The PF0 signal is driven low and remains low until

VCCI returns to nominal conditions. During nominal supply conditions CEO will follow CEI and WEO

will follow WEI . The fourth function which the DS1710 performs is a battery status warning so that

potential data loss is avoided. Each time VCCI is applied to the device battery status is checked with a

precision comparator. If during battery backup, no switch occurred from one battery to the other, the

voltage of the battery supplying power when VCCI is applied is checked. If this voltage is less than 2.0

volts the second chip enable cycle after power is applied is inhibited. If any switch from one battery to

another did occur the voltage of both batteries is checked. If either voltage is less than 2.0 volts the

second chip enable cycle will be inhibited. Battery status can therefore be determined by performing a

DS1710 Datasheet(PDF) 2 Page - Dallas Semiconductor

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