.
.
.
.
.
鈭?/div>
2
.
465
Lithium-ion batteries typically require float voltage accu-
racy of 1% to 2%. Accuracy of the LT1510 OVP voltage is
鹵0.5%
at 25擄C and
鹵1%
over full temperature. This leads
to the possibility that very accurate (0.1%) resistors might
be needed for R3 and R4. Actually, the temperature of the
LT1510 will rarely exceed 50擄C in float mode because
charging currents have tapered off to a low level, so 0.25%
resistors will normally provide the required level of overall
accuracy.
External Shutdown
The LT1510 can be externally shut down by pulling the V
C
pin low with an open drain MOSFET, such as VN2222. The
V
C
pin should be pulled below 0.8V at room temperature
to ensure shutdown. This threshold decreases at about
2mV/擄C. A diode connected between the MOSFET drain
and the V
C
pin will still ensure the shutdown state over all
temperatures, but it results in slightly different conditions
as outlined below.
If the V
C
pin is held below threshold, but above
鈮?/div>
0.4V, the
current flowing
into
the BAT pin will remain at about
700碌A(chǔ). Pulling the V
C
pin below 0.4V will cause the current
to drop to
鈮?/div>
200碌A(chǔ) and reverse, flowing
out
of the BAT pin.
Although these currents are low, the long term effect may
need to be considered if the charger is held in a shutdown
state for very long periods of time, with the charger input
voltage remaining. Removing the charger input voltage
causes all currents to drop to near zero.
If it is acceptable to have 200碌A(chǔ) flowing into the battery
while the charger is in shutdown, simply pull the V
C
pin
directly to ground with the external MOSFET. The resistor
divider used to sense battery voltage will pull current out
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