ADM8693ARN Analog Devices Inc, ADM8693ARN Datasheet - Page 10

• Manufacturer Part Number: ADM8693ARN
• Description: IMPROVED ADM693 I.C.
• Manufacturer: Analog Devices Inc
• Type: Battery Backup Circuitr

Specifications of ADM8693ARN

• Rohs Compliant: NO
• Rohs Status: RoHS non-compliant
• Number Of Voltages Monitored: 1
• Output: Push-Pull, Push-Pull
• Reset: Active High/Active Low
• Reset Timeout: 35 ms Minimum
• Voltage - Threshold: 4.4V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)

ADM8690/ADM8691/ADM8692/ADM8693/ADM8694/ADM8695
CIRCUIT INFORMATION
BATTERY SWITCHOVER SECTION
The battery switchover circuit compares V
and connects V
when V
is 70 mV greater than V
hysteresis prevents repeated rapid switching if V
slowly or remains nearly equal to the battery voltage.
During normal operation, with V
is internally switched to V
sistor switch. This switch has a typical on resistance of 0.7 Ω
and can supply up to 100 mA at the V
normally used to drive a RAM memory bank, requiring
instantaneous currents of greater than 100 mA. If this is the
case, a bypass capacitor should be connected to V
capacitor provides the peak current transients to the RAM.
A capacitance value of 0.1 μF or greater can be used.
If the continuous output current requirement at V
100 mA, or if a lower V
an external PNP pass transistor can be connected in parallel
with the internal transistor. The BATT ON output (ADM8691/
ADM8693/ADM8695) can directly drive the base of the
external transistor.
A 7 Ω MOSFET switch connects the V
battery backup. This MOSFET has very low input-to-output
differential (dropout voltage) at the low current levels required
for battery back up of CMOS RAM or other low power CMOS
circuitry. The supply current in battery back up is typically 0.4 μA.
The ADM8690/ADM8691/ADM8694/ADM8695 operate with
battery voltages from 2.0 V to 4.25 V, and the ADM8692/
ADM8693 operate with battery voltages from 2.0 V to 4.0 V.
High value capacitors, either standard electrolytic or the farad-
size, double-layer capacitors, can also be used for short-term
memory backup. A small charging current of typically 10 nA
(0.1 μA maximum) flows out of the V
is useful for maintaining rechargeable batteries in a fully
V
BATT
V
CC
CC
is 50 mV higher than V
700
mV
Figure 14. Battery Switchover Schematic
OUT
100
mV
to whichever is higher. Switchover occurs
GATE DRIVE
CC
BATT
− V
OUT
as V
OUT
through an internal PMOS tran-
INTERNAL
SHUTDOWN SIGNAL
WHEN
V
CC
BATT
voltage differential is desired,
CC
BATT
rises. This 20 mV of
higher than V
> (V
BATT
OUT
as V
BATT
CC
terminal. V
terminal. This current
CC
CC
+ 0.7V)
input to V
to the V
falls, and when V
CC
OUT
BATT
OUT
V
BATT ON
(ADM8690,
ADM8695)
falls very
OUT
. The
OUT
BATT
OUT
, V
exceeds
CC
is
during
input,
Rev. A | Page 10 of 20
CC
charged condition. This extends the life of the backup battery by
compensating for its self-discharge current. Also note that this
current poses no problem when lithium batteries are used for
backup because the maximum charging current (0.1 μA) is safe
for even the smallest lithium cells.
If the battery switchover section is not used, V
connected to GND and V
POWER-FAIL RESET OUTPUT
RESET is an active low output that provides a RESET signal to
the microprocessor whenever V
V
low. The nominal reset voltage threshold is 4.65 V (ADM8690/
ADM8691/ADM8694/ADM8695) or 4.4 V (ADM8692/
ADM8693).
LOW LINE
On power-up, RESET remains low for 50 ms (200 ms for
ADM8694 and ADM8695) after V
reset threshold. This allows time for the power supply and micro-
processor to stabilize. On power-down, the RESET output remains
low with V
is held in a stable shutdown condition.
This RESET active time is adjustable on the ADM8691/ADM8693/
ADM8695 by using an external oscillator or by connecting an
external capacitor to the OSC IN pin. Refer to Table 5 and
Figure 17, Figure 18, Figure 19, and Figure 20.
The guaranteed minimum and maximum thresholds of the
ADM8690/ADM8691/ADM8694/ADM8695 are 4.5 V and
4.73 V, and the guaranteed thresholds of the ADM8692/ADM8693
are 4.25 V and 4.48 V. The ADM8690/ADM8691/ADM8694/
ADM8695 are, therefore, compatible with 5 V supplies with a
+10%, −5% tolerance and the ADM8692/ADM8693 are com-
patible with 5 V ± 10% supplies. The reset threshold comparator
has approximately 50 mV of hysteresis. The response time of
the reset voltage comparator is less than1 μs. If glitches are
present on the V
V
CC
CC
RESET
should be decoupled close to the device.
falls below the reset threshold, the RESET output is forced
V
CC
CC
as low as 1 V. This ensures that the microprocessor
V2
CC
t
Figure 15. Power-Fail Reset Timing
1
line that could cause spurious reset pulses,
t 1 = RESET TIME
V1 = RESET VOLTAGE THRESHOLD LOW
V2 = RESET VOLTAGE THRESHOLD HIGH
HYSTERESIS = V2–V1
OUT
V1
should be connected to V
CC
is at an invalid level. When
CC
rises above the appropriate
V2
t
1
BATT
should be
CC
.
V1