DS1321S/T&R Maxim Integrated Products, DS1321S/T&R Datasheet - Page 2

• Manufacturer Part Number: DS1321S/T&R
• Description: IC CTRLR NV W/BATT MON 5V 16SOIC
• Manufacturer: Maxim Integrated Products

Specifications of DS1321S/T&R

• Controller Type: Nonvolatile RAM
• Voltage - Supply: 4.75 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

DS1321
DESCRIPTION
The DS1321 Flexible Nonvolatile Controller with Lithium Battery Monitor is a CMOS circuit which
solves the application problem of converting CMOS SRAMs into nonvolatile memory. Incoming power
is monitored for an out-of-tolerance condition. When such a condition is detected, chip enable outputs are
inhibited to accomplish write protection and the battery is switched on to supply the SRAMs with
uninterrupted power. Special circuitry uses a low-leakage CMOS process which affords precise voltage
detection at extremely low battery consumption. One DS1321 can support as many as four SRAMs
arranged in any of three memory configurations.
In addition to battery-backup support, the DS1321 performs the important function of monitoring the
remaining capacity of the lithium battery and providing a warning before the battery reaches end-of-life.
Because the open-circuit voltage of a lithium backup battery remains relatively constant over the majority
of its life, accurate battery monitoring requires loaded-battery voltage measurement. The DS1321
performs such measurement by periodically comparing the voltage of the battery as it supports an internal
resistive load with a carefully selected reference voltage. If the battery voltage falls below the reference
voltage under such conditions, the battery will soon reach end-of-life. As a result, the Battery Warning
pin is activated to signal the need for battery replacement.
MEMORY BACKUP
The DS1321 performs all the circuit functions required to provide battery-backup for as many as four
SRAMs. First, the device provides a switch to direct power from the battery or the system power supply
(V
). Whenever V
is less than the V
trip point and V
is less than the battery voltage V
, the
CCI
CCI
CCTP
CCI
BAT
battery is switched in to provide backup power to the SRAM. This switch has voltage drop of less than
0.2 volts.
Second, the DS1321 handles power failure detection and SRAM write-protection. V
is constantly
CCI
monitored, and when the supply goes out of tolerance, a precision comparator detects power failure and
inhibits the four chip enable outputs in order to write-protect the SRAMs. This is accomplished by
holding
through
to within 0.2 volts of V
when V
is out of tolerance. If any
is
CEO1
CEO4
CEI
CCO
CCI
active (low) at the time that power failure is detected, the corresponding
signal is kept low until the
CEO
signal is brought high again. Once the
signal is brought high, the
signal is taken high and
CEI
CEI
CEO
held high until after V
has returned to its nominal voltage level. If the
signal is not brought high
CEI
CCI
by 1.5 µs after power failure is detected, the corresponding
is forced high at that time. This specific
CEO
scheme for delaying write protection for up to 1.5 µs guarantees that any memory access in progress
when power failure occurs will complete properly. Power failure detection occurs in the range of 4.75 to
4.5 volts (5% tolerance) when the TOL pin is wired to GND or in the range of 4.5 to 4.25 volts (10%
tolerance) when TOL is connected to V
.
CCO
2 of 12