LTC4066 LINER [Linear Technology], LTC4066 Datasheet - Page 18

• Manufacturer Part Number: LTC4066
• Description: USB Power Controller and Li-Ion Linear Charger with Low Loss Ideal Diode
• Manufacturer: LINER [Linear Technology]

LTC4066/LTC4066-1
APPLICATIONS INFORMATION
Programming Charge Current
The formula for the battery charge current is:
where V
total resistance from the PROG pin to ground. Keep in
mind that when the LTC4066/LTC4066-1 are powered
from the IN pin, the programmed input current limit takes
precedence over the charge current. In such a scenario,
the charge current cannot exceed the programmed input
current limit.
For example, if typical 500mA charge current is required,
calculate:
For best stability over temperature and time, 1% metal
fi lm resistors are recommended. Under trickle charge
conditions, this current is reduced to 10% of the full-
scale value.
Monitoring Charge Current
The I
the BAT pin current. The I
to one-thousandth of the absolute value of the current
fl owing in the BAT pin. The POL pin indicates the polarity
of the BAT pin current. When current is fl owing from OUT
to BAT (i.e., charging), the POL pin pulls to ground. When
current is fl owing from BAT to OUT (ideal diode), the POL
pin assumes a high impedance. If a resistor, R
placed from the I
BAT current is:
18
I
R
I
CHG
BAT
PROG
STAT
=
PROG
=
and POL pins provide a means for monitoring
(
=
R
I
V
PROG
ISTAT
ISTAT
⎛
⎜
⎝
500
is the PROG pin voltage and R
1
)
STAT
V
mA
•
• 1000
50 000
⎞
⎟
⎠
pin to ground, then the formula for
,
•
50 000 100
STAT
=
,
R
pin sources a current equal
V
PROG
PROG
=
•
50 000
k
,
PROG
ISTAT
is the
, is
where V
resistance from the I
a true gas gauge function to be performed on the battery
with an external ADC and integrator. See Gas Gauge for
more information.
The Charge Timer
The programmable charge timer is used to terminate the
charge cycle. The timer duration is programmed by an
external capacitor at the TIMER pin. The charge time is
typically:
The timer starts when an input voltage greater than the
undervoltage lockout threshold level is applied or when
leaving shutdown and the voltage on the battery is less than
the recharge threshold. At power-up or exiting shutdown
with the battery voltage less than the recharge threshold,
the charge time is a full cycle. If the battery is greater than
the recharge threshold, the timer will not start and charging
is prevented. If after power-up the battery voltage drops
below the recharge threshold, or if after a charge cycle
the battery voltage is still below the recharge threshold,
the charge time is set to one-half of a full cycle.
The LTC4066/LTC4066-1 have a feature that extends charge
time automatically. Charge time is extended if the charge
current in constant-current mode is reduced due to load
current or thermal regulation. This change in charge time
is inversely proportional to the change in charge current.
As the LTC4066/LTC4066-1 approach constant-voltage
mode the charge current begins to drop. This change in
charge current is due to normal charging operation and
does not affect the timer duration.
t
TIMER
ISTAT
(
Hours
is the I
)
=
STAT
STAT
C
TIMER
pin voltage and R
pin to ground. These pins enable
0 1
.
•
R
μ
PROG
F
•
100
•
3
k
Hours
ISTAT
is the total
4066fc