ADM8690–ADM8695
P IN CO NFIGURATIO NS
V
1
2
3
4
5
6
7
8
16 RESET
RESET
BATT
V
V
BATT
1
2
3
4
8
7
6
5
15
OUT
V
OUT
ADM8690
ADM8692
ADM8694
ADM8691
ADM8693
ADM8695
TOP VIEW
(Not to Scale)
V
RESET
WDI
CC
V
14 WDO
CC
GND
PFI
GND
13 CE
IN
TOP VIEW
(Not to Scale)
PFO
BATT ON
CE
OUT
12
11
10
9
WDI
PFO
PFI
LOW LINE
OSC IN
OSC SEL
P RO D UCT SELECTIO N GUID E
P art
Num ber
Nom inal Reset
Tim e
Nom inal VCC
Reset Threshold
Nom inal Watchdog
Tim eout P eriod
Battery Backup
Switching
Base D rive
Ext P NP
Chip Enable
Signals
ADM8690
ADM8691
ADM8692
ADM8693
ADM8694
ADM8695
50 ms
50 ms or ADJ
50 ms
50 ms or ADJ
200 ms
200 ms or ADJ
4.65 V
4.65 V
4.4 V
4.4 V
4.65 V
4.65 V
1.6 s
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
100 ms, 1.6 s, ADJ
1.6 s
100 ms, 1.6 s, ADJ
1.6 s
100 ms, 1.6 s, ADJ
CIRCUIT INFO RMATIO N
Batter y Switchover Section
If the continuous output current requirement at VOUT exceeds
100 mA, or if a lower VCC–VOUT voltage differential is desired,
an external PNP pass transistor may be connected in parallel with
the internal transistor. T he BAT T ON output (ADM8691/
ADM8693/ADM8695) can directly drive the base of the exter-
nal transistor.
T he battery switchover circuit compares VCC to the VBAT T
input, and connects VOUT to whichever is higher. Switchover
occurs when VCC is 50 mV higher than VBAT T as VCC falls, and
when VCC is 70 mV greater than VBAT T as VCC rises. T his
20 mV of hysteresis prevents repeated rapid switching if VCC
falls very slowly or remains nearly equal to the battery voltage.
A 7 Ω MOSFET switch connects the VBAT T input to VOUT dur-
ing battery backup. T his MOSFET has very low input-to-out-
put differential (dropout voltage) at the low current levels
required for battery back up of CMOS RAM or other low power
CMOS circuitry. T he supply current in battery back up is typi-
cally 0.4 µA.
V
CC
V
OUT
V
BATT
T he ADM8690/ADM8691/ADM8694/ADM8695 operates with
battery voltages from 2.0 V to 4.25 V, and the ADM8692/
ADM8693 operates 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 max) flows out of the VBAT T terminal. T his current is
useful for maintaining rechargeable batteries in a fully charged
condition. T his extends the life of the backup battery by com-
pensating for its self discharge current. Also note that this cur-
rent poses no problem when lithium batteries are used for
backup since the maximum charging current (0.1 µA) is safe for
even the smallest lithium cells.
GATE DRIVE
100
mV
BATT ON
(ADM8690,
ADM8695)
INTERNAL
SHUTDOWN SIGNAL
WHEN
700
mV
V
> (V + 0.7V)
BATT
CC
Figure 1. Battery Switchover Schem atic
During normal operation, with VCC higher than VBAT T, VCC is
internally switched to VOUT via an internal PMOS transistor
switch. T his switch has a typical on-resistance of 0.7 Ω and can
supply up to 100 mA at the VOUT terminal. VOUT is normally
used to drive a RAM memory bank which may require instanta-
neous currents of greater than 100 mA. If this is the case then a
bypass capacitor should be connected to VOUT . T he capacitor
will provide the peak current transients to the RAM. A capaci-
tance value of 0.1 µF or greater may be used.
If the battery switchover section is not used, VBAT T should be
connected to GND and VOUT should be connected to VCC
.
REV. 0
–5–
ADI [ ADI ]
