LTC4066 LINER [Linear Technology], LTC4066 Datasheet - Page 22

• 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
Any time a battery is connected to the BAT pin and the
SHDN pin is low, the BAT pin current can be monitored
with the following equation:
where |I
V
resistance from the I
The POL pin has two states: high impedance and strong
pull-down. High impedance indicates that current is fl ow-
ing from BAT to OUT (ideal diode function) and strong
pull-down indicates that current is fl owing from OUT to
BAT (charging). If an external ADC is used to convert the
I
sign bit.
When the ideal diode function is operating, the I
cannot monitor ideal diode load currents less than about
1mA. For any ideal diode load current less than 1mA, the
I
1μA. However, when the battery charger function is operat-
ing, the I
of the battery charge current even if the charge current
drops to less than 1mA.
When choosing the value of R
considered. For the battery charger function, the value of
R
pin transitions to its high impedance state (see CHRG
Status Output Pin). Furthermore, the available common
mode range on the I
ratio between I
I
– 0.5V. When the ideal diode is functioning, the I
22
STAT
STAT
STAT
ISTAT
ISTAT
I
BAT
pin will source a constant current of approximately
pin voltage should not exceed approximately V
voltage, then the POL pin can be thought of as a
programs the charge current below which the CHRG
is the voltage on the I
BAT
=
STAT
R
V
| is the absolute value of the BAT pin current,
ISTAT
ISTAT
pin will continue to source one-thousandth
BAT
and I
• 1000
STAT
STAT
ISTAT
pin needed to maintain an accurate
pin to ground.
STAT
is limited. When charging, the
ISTAT
pin and R
, two details must be
ISTAT
is the total
STAT
STAT
OUT
pin
pin
voltage should not exceed approximately V
the typical minimum operating voltage for the ideal diode
this value would be 2.8V – 0.5V = 2.3V). Typically, it is this
second case that is the limiting situation since V
cally lower than V
diode loads tend to be greater than typical charge currents
(causing a higher voltage on the I
choosing a value of R
current may limit the maximum ideal diode load current
that can be sensed accurately. Consider an example:
Calculate:
In this example, there is no common mode problem because
the maximum I
minimum. However, if, instead of 100mA, the desired CHRG
detection current was lowered to 40mA, then the desired
R
the maximum I
suming no change in the 1.5A maximum ideal diode cur-
rent). Therefore, ideal diode currents greater than 920mA
(2.3V/2.5k • 1000) might not be reported accurately. To
calculate the maximum ideal diode current that will be
reported accurately:
ISTAT
a) Desired charge current = 850mA
b) Desired CHRG detection current = 100mA
c) Maximum transient ideal diode current = 1.5A
a) R
b) R
c) V
I
DMON MAX
ISTAT(MAX)
PROG
resistor would increase to 2.5k (100V/40mA) and
ISTAT
(
= (1V/850mA) • 50,000 = 59k
= 100V/100mA = 1k
)
STAT
STAT
=
= 1.5A/1000 • 1k = 1.5V
OUT
V
BAT
voltage (1.5V) is well below the 2.3V
voltage would increase to 3.75V (as-
R
(while charging) and transient ideal
ISTAT
ISTAT
– .
0 5
based on the CHRG detection
V
STAT
pin). Therefore,
BAT
– 0.5V (for
BAT
is typi-
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