LTC4055 Linear Technology, LTC4055 Datasheet - Page 18

• Manufacturer Part Number: LTC4055
• Description: USB Power Controller and Li-Ion Linear Charger
• Manufacturer: Linear Technology

OPERATIO
LTC4055
The nearest 1% value for R
used to bias the NTC thermistor to get cold and hot trip
points of approximately 0 C and 44 C respectively. To
extend the delta between the cold and hot trip points a
resistor, R1, can be added in series with R
Figure 3b). The values of the resistors are calculated as
follows:
where R
R
trip points. Continuing the example from before with a
desired hot trip point of 50 C:
The final solution is as shown if Figure 3b where R
121k, R1 = 13.3k and R
CURRENT LIMIT UNDERVOLTAGE LOCKOUT
An internal undervoltage lockout circuit monitors the input
voltage and keeps the current limit circuits of the part in
shutdown mode until V
lockout threshold. The current limit UVLO circuit has a
built-in hysteresis of 125mV. Furthermore, to protect
against reverse current in the power MOSFET, the current
limit UVLO circuit keeps the current limit shutdown if V
exceeds V
tripped, the current limit circuits will not come out of
shutdown until V
18
R
R
COLD
NOM
1 100
R
R
NOM
1
13.3k, 13.3k is nearest 1%
are the values of R
120.8k, 121k is nearest 1%
2 815 0 4086
k
NOM
R
2 815 0 4086
.
•
.
COLD
IN
2 815 0 4086
R
.
. If the current limit UVLO comparator is
0 4086
COLD
is the value of the bias resistor, R
2 815 0 4086
.
– .
– .
.
–
– .
R
OUT
U
0 4086
–
HOT
.
R
– .
HOT
falls 50mV below the V
NTC
IN
•
100
NTC
R
rises above the undervoltage
NOM
=100k at 25 C.
COLD
k
2 815 0 4086
• .
at the desired temperature
• .
.
3 266 0 3602
is 115k. This is the value
3 266 0 3602
–
R
– .
HOT
– .
– .
–
R
HOT
IN
voltage.
– .
NTC
HOT
0 3602
NOM
(see
and
OUT
=
CHARGER UNDERVOLTAGE LOCKOUT
Internal undervoltage lockout circuits monitor the V
V
shut down until V
lockout threshold. The charger UVLO circuit has a built-in
hysteresis of 125mV. Furthermore, to protect against
reverse current in the power MOSFET, the charger UVLO
circuit keeps the charger shutdown if V
If the charger UVLO comparator is tripped, the charger
circuits will not come out of shutdown until V
V
SHUTDOWN
The LTC4055 can be shut down by forcing the SHDN pin
greater than 1V. In shutdown, the currents on IN1/IN2,
OUT and BAT are decreased to less than 2.5 A and the
internal battery charge timer is reset. All power paths are
put in a Hi-Z state.
SUSPEND
The LTC4055 can be put in suspend mode by forcing the
SUSP pin greater than 1V. In suspend mode the ideal diode
function from BAT to OUT and the output charger are kept
alive. The rest of the part is shut down to conserve current
and the battery charge timer is reset if V
than V
V
Many types of capacitors can be used for input bypassing.
However, caution must be exercised when using multi-
layer ceramic capacitors. Because of the self resonant and
high Q characteristics of some types of ceramic capaci-
tors, high voltage transients can be generated under some
start-up conditions, such as connecting the charger input
to a hot power source. For more information, refer to
Application Note 88.
OUT
BAT
IN
and Wall Adaptor Bypass Capacitor
by 50mV.
voltages and keep the charger circuits of the part
BAT
.
IN
or V
OUT
rises above the under-voltage
BAT
OUT
exceeds V
becomes less
OUT
exceeds
IN
OUT
4055p
and
.