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LTC4095EDC#TRMPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
LTC4095
10
4095fa
OPERATION
Figure 2. State Diagram of LTC4095 Operation
NTC Thermistor
The battery temperature is measured by placing a nega-
tive temperature coeffi cient (NTC) thermistor close to the
battery pack. The NTC circuitry is shown in Figure 3.
To use this feature, connect the NTC thermistor, R
NTC
,
between the NTC pin and ground, and a bias resistor,
R
NOM
, from IN to NTC. R
NOM
should be a 1% resistor with
a value equal to the value of the chosen NTC thermistor
at 25°C (R25). A 100k thermistor is recommended since
thermistor current is not measured by the LTC4095 and
its current will have to be considered for compliance with
USB specifi cations.
The LTC4095 will pause charging when the resistance of
the NTC thermistor drops to 0.54 times the value of R25
or approximately 54k (for a Vishay “Curve 1” thermistor,
this corresponds to approximately 40°C). If the battery
charger is in constant voltage mode, the safety timer will
pause until the thermistor indicates a return to a valid
temperature.
As the temperature drops, the resistance of the NTC therm-
istor rises. The LTC4095 is also designed to pause charging
when the value of the NTC thermistor increases to 3.25
times the value of R25. For a Vishay “Curve 1” thermistor,
this resistance, 325k, corresponds to approximately 0°C.
The hot and cold comparators each have approximately
3°C of hysteresis to prevent oscillation about the trip point.
Grounding the NTC pin disables all NTC functionality.
IF SUSP < 0.4V AND
IN > 4V AND
IN > BAT + 165mV
DUVLO, UVLO AND SUSPEND SUSPEND/SHUTDOWN MODE
1/10 FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
30 MINUTE TIMER BEGINS
TRICKLE CHARGE MODE
FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
CONSTANT CURRENT MODE
BATTERY CHARGING SUSPENDED
CHRG PULSES
NTC FAULT
NO CHARGE CURRENT
CHRG PULSES
DEFECTIVE BATTERY
4 HOUR TERMINATION
TIMER BEGINS
BAT DROPS BELOW 0.105V
4 HOUR TERMINATION TIMER RESETS
CONSTANT VOLTAGE MODE
NO CHARGE CURRENT
CHRG HIGH IMPEDANCE
STANDBY MODE
CHRG HIGH IMPEDANCE
BAT > 2.9V
4095 F02
NO FAULT, BAT ≤ 2.9V
30 MINUTE
TIMEOUT
4 HOUR CHARGE
CYCLE BEGINS
2.9V < BAT < 4.105V
TRUE
4 HOUR
TIMEOUT
NO FAULT
FAULT
FALSE
POWER
ON
LTC4095
11
4095fa
APPLICATIONS INFORMATION
Alternate NTC Thermistors and Biasing
The LTC4095 provides temperature qualifi ed charging if a
grounded thermistor and a bias resistor are connected to
the NTC pin. By using a bias resistor whose value is equal
to the room temperature resistance of the thermistor (R25)
the upper and lower temperatures are pre-programmed
to approximately 40°C and 0°C, respectively (assuming
a Vishay “Curve 1” thermistor).
The upper and lower temperature thresholds can be ad-
justed by either a modifi cation of the bias resistor value
or by adding a second adjustment resistor to the circuit.
If only the bias resistor is adjusted, then either the upper
or the lower threshold can be modifi ed but not both. The
other trip point will be determined by the characteristics
of the thermistor. Using the bias resistor in addition to an
adjustment resistor, both the upper and the lower tempera-
ture trip points can be independently programmed with
the constraint that the difference between the upper and
lower temperature thresholds cannot decrease. Examples
of each technique are given below.
NTC thermistors have temperature characteristics which
are indicated on resistance-temperature conversion tables.
The Vishay-Dale thermistor NTHS0603N011-N1003F, used
in the following examples, has a nominal value of 100k
and follows the Vishay “Curve 1” resistance-temperature
characteristic.
In the explanation below, the following notation is used.
R25 = Value of the thermistor at 25°C
R
NTC|COLD
= Value of thermistor at the cold trip point
R
NTC|HOT
= Value of the thermistor at the hot trip point
r
COLD
= Ratio of R
NTC|COLD
to R25
r
HOT
= Ratio of R
NTC|HOT
to R25
R
NOM
= Primary thermistor bias resistor (see Figure 3)
R1 = Optional temperature range adjustment resistor (see
Figure 4)
The trip points for the LTC4095’s temperature qualifi ca-
tion are internally programmed at 0.349 • IN for the hot
threshold and 0.765 • IN for the cold threshold.
Therefore, the hot trip point is set when:
R
RR
IN IN
NTC HOT
NOM NTCHOT
|
|
•.•
+
= 0 349
and the cold trip point is set when:
R
RR
IN IN
NTC COLD
NOM NTC COLD
|
|
•.•
+
= 0 765
Figure 4. NTC Thermistor Circuit with Additional Bias Resistor
Figure 3. Typical NTC Thermistor Circuit
4095 F03
R
NOM
100k
R
NTC
100k
–
+
–
+
–
+
TOO_COLD
TOO_HOT
NTC_ENABLE
0.765 • IN
(NTC
RISING)
LTC4095 NTC BLOCK
0.349 • IN
(NTC
FALLING)
6
NTC
8
IN
0.017 • IN
(NTC FALLING)
4095 F04
R
NOM
105k
R
NTC
100k
–
+
–
+
–
+
TOO_COLD
TOO_HOT
NTC_ENABLE
R1
12.7k
0.765 • IN
(NTC
RISING)
0.349 • IN
(NTC
FALLING)
6
NTC
0.017 • IN
(NTC FALLING)
8
IN
LTC4095
12
4095fa
APPLICATIONS INFORMATION
Figure 5. Combining Wall Adapter and USB Power
Solving these equations for R
NTC|COLD
and R
NTC|HOT
results in the following:
R
NTC|HOT
= 0.536 • R
NOM
and
R
NTC|COLD
= 3.25 • R
NOM
By setting R
NOM
equal to R25, the above equations result
in r
HOT
= 0.536 and r
COLD
= 3.25. Referencing these ratios
to the Vishay Resistance-Temperature Curve 1 chart gives
a hot trip point of about 40°C and a cold trip point of about
0°C. The difference between the hot and cold trip points
is approximately 40°C.
By using a bias resistor, R
NOM
, different in value from
R25, the hot and cold trip points can be moved in either
direction. The temperature span will change somewhat due
to the nonlinear behavior of the thermistor. The following
equations can be used to easily calculate a new value for
the bias resistor:
R
r
R
R
r
R
NOM
HOT
NOM
COLD
=
=
0 536
25
325
25
.
•
.
•
where r
HOT
and r
COLD
are the resistance ratios at the
de-
sired
hot and cold trip points. Note that these equations
are linked. Therefore, only one of the two trip points can
be chosen, the other is determined by the default ratios
designed in the IC. Consider an example where a 60°C
hot trip point is desired.
From the Vishay Curve 1 R-T characteristics, r
HOT
is 0.2488
at 60°C. Using the above equation, R
NOM
should be set
to 46.4k. With this value of R
NOM
, the cold trip point is
about 16°C. Notice that the span is now 44°C rather than
the previous 40°C.
The upper and lower temperature trip points can be inde-
pendently programmed by using an additional bias resistor
as shown in Figure 4. The following formulas can be used
to compute the values of R
NOM
and R
1
:
R
rr
R
RRr
NOM
COLD HOT
NOM HOT
=
=
–
.
•
.• – •
2 714
25
1 0 536 RR25
For example, to set the trip points to 0°C and 45°C with
a Vishay Curve 1 thermistor choose:
Rkk
NOM
==
3 266 0 4368
2 714
100 104 2
.–.
.
•.
the nearest 1% value is 105k.
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k
the nearest 1% value is 12.7k. The fi nal solution is shown
in Figure 4 and results in an upper trip point of 45°C and
a lower trip point of 0°C.
USB and Wall Adapter Power
Although the LTC4095 is designed to draw power from a
USB port to charge Li-Ion batteries, a wall adapter can also
be used. Figure 5 shows an example of how to combine
wall adapter and USB power inputs. A P-channel MOSFET,
MP1, is used to prevent back conduction into the USB
port when a wall adapter is present and Schottky diode,
D1, is used to prevent USB power loss through the 1k
pull-down resistor.
Typically, a wall adapter can supply signifi cantly more
current than the 500mA-limited USB port. Therefore, an
N-channel MOSFET, MN1, and an extra program resistor
are used to increase the maximum charge current to
950mA when the wall adapter is present.
IN
MP1
MN1
1k
1.74k
1.65k
1
I
BAT
8
7
Li-Ion
BATTERY
4095 F05
LTC4095
BAT
USB
POWER
500mA I
CHG
5V WALL
ADAPTER
950mA I
CHG
PROG
+
D1
Power Dissipation
The conditions that cause the LTC4095 to reduce charge
current through thermal feedback can be approximated
by considering the power dissipated in the IC. For high
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LTC4095EDC#TRMPBF

Mfr. #:
Buy LTC4095EDC#TRMPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Battery Management Standalone 950mA USB Li-Ion/Polymer Battery Charger in DFN
Lifecycle:
New from this manufacturer.
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