Datasheet

LTC690/LTC691
LTC694/LTC695
6
690ff
For more information www.linear.com/690
block DiagraM
CHARGE
PUMP
M2
M1
V
BATT
V
CC
CE IN
PFI
OSC IN
OSC SEL
WDI
RESET PULSE
GENERATOR
WATCHDOG
TIMER
RESET
BATT ON
V
OUT
C1
1.3V
GND
–
+
–
+
C2
OSC
TRANSITION
DETECTOR
–
+
C3
WDO
RESET
PFO
LOWLINE
CE OUT
690 BD
pin FuncTions
V
CC
: 5V Supply Input. The V
CC
pin should be bypassed
with a 0.1µF capacitor.
V
OUT
: Voltage Output for Backed Up Memory. Bypass with
a capacitor of 0.1µF or greater. During normal operation,
V
OUT
obtains power from V
CC
through an NMOS power
switch, M1, which can deliver up to 50mA and has a typical
on resistance of 5Ω. When V
CC
is lower than V
BATT
, V
OUT
is internally switched to V
BATT
. If V
OUT
and V
BATT
are not
used, connect V
OUT
to V
CC
.
V
BATT
: Back-Up Battery Input. When V
CC
falls below V
BATT
,
auxiliary power, connected to V
BATT
, is delivered to V
OUT
through PMOS switch, M2. If back-up battery or auxiliary
power is not used, V
BATT
should be connected to GND.
GND: Ground pin.
BATT ON: Battery On Logic Output from Comparator C2.
BATT ON goes low when V
OUT
is internally connected to
V
CC
. The output typically sinks 35mA and can provide
base drive for an external PNP transistor to increase the
output current above the 50mA rating of V
OUT
. BATT ON
goes high when V
OUT
is internally switched to V
BATT
.
PFI: Power Failure Input. PFI is the noninverting input
to
the power-fail comparator, C3. The inverting input is
internally connected to a 1.3V reference. The power failure
output remains high when PFI is above 1.3V and goes
low when PFI is below 1.3V. Connect PFI to GND or V
OUT
when C3 is not used.