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PDF LTC4079 Data sheet ( Hoja de datos )
| Número de pieza | LTC4079 | |
| Descripción | 250mA Linear Charger | |
| Fabricantes | Linear | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC4079 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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LTC4079
60V, 250mA Linear Charger
with Low Quiescent Current
Features
n Wide Input Voltage Range: 2.7V to 60V
n Adjustable Battery Voltage: 1.2V to 60V
n Adjustable Charge Current: 10mA to 250mA
n Low Quiescent Current While Charging: IIN = 4µA
n Ultralow Battery Drain When Shutdown or Charged:
IBAT < 0.01µA
n Auto Recharge
n Input Voltage Regulation for High Impedance Sources
n Thermal Regulation Maximizes Output Current
without Overheating
n Constant Voltage Feedback with ±0.5% Accuracy
n NTC Thermistor Input for Temperature Qualified
Charging
n Adjustable Safety Timer
n Charging Status Indication
n Thermally Enhanced 10-Lead (3mm × 3mm)
DFN Package
Applications
n Embedded Automotive and Industrial
n Backup Battery Charging from Another Battery
n Energy Harvesting Charger
n Thin Film Battery Products
Description
The LTC®4079 is a low quiescent current, high voltage
linear charger for most battery chemistry types including
Li-Ion/Polymer, Lead-Acid or NiMH battery stacks up to
60V. The maximum charge current is adjustable from
10mA to 250mA with an external resistor. The battery
charge voltage is set using an external resistor divider.
With an integrated power device, current sensing and
reverse current protection, a complete charging solution
using the LTC4079 requires very few external components.
Thermal regulation ensures maximum charge current up to
the specified limit without the risk of overheating. Charging
can be terminated by either C/10 or adjustable timer.
Input voltage regulation reduces charge current when
the input voltage falls to an adjustable level or the battery
voltage, making it well suited for energy harvesting
applications. Other features include temperature qualified
charging, bad battery detection, automatic recharge with
sampled feedback in standby for negligible battery drain,
and an open-drain CHRG status output. The device is
offered in a compact, thermally enhanced 10-lead (3mm
× 3mm) DFN package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Typical Application
9V TO 60V
Charging a Backup Battery
IN BAT
1µF LTC4079
EN FB
3.01k
CHRG
FBG
PROG NTCBIAS
TIMER NTC
GND
1.54M
249k
8.4V
10k
+
T 10k
Li-Ion
4079 TA01a
Li-Ion Battery Charge Cycle
140
500mAh 2-CELL LI-ION
120
100 IBAT
VBAT
8.6
8.4
8.2
80 8.0
60 7.8
40
C/10
TERMINATION
7.6
20 7.4
0 7.2
012345678
TIME (HOURS)
4079 TA01b
For more information www.linear.com/LTC4079
4079f
1
1 page  
LTC4079
Typical Performance Characteristics VIN = 12V, TA = 25°C unless otherwise noted.
Regulated Feedback Voltage
vs Temperature
1.182
1.178
1.174
1.170
1.166
INTERNAL REFERENCE
ONSET OF
THERMAL REGULATION
1.162
1.158
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
4079 G01
Input Supply Quiescent Current
vs Temperature
6 VFB = 1.2V
5 (IBAT = 0)
CHARGING
4
3 STANDBY
(CHARGING TERMINATED)
2
1
SHUTDOWN (EN = 0)
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
4079 G04
Regulated Feedback Voltage
vs VIN
1.182
1.178
1.174
1.170
1.166
1.162
1.158
0
10 20 30 40 50 60
VIN (V)
4079 G02
Input Supply Quiescent Current
vs Supply Voltage
5 CHARGING
4
VFB = 1.2V
(IBAT = 0)
3
STANDBY
2 (CHARGING TERMINATED)
1
SHUTDOWN (EN = 0)
0
0 10 20 30 40 50 60
VIN (V)
4079 G05
Load Regulation of Regulated
Feedback Voltage
1.182
RPROG = 1.2k
1.178 ICHG = 248mA
1.174
1.170
1.166
1.162
1.158
0
50 100 150 200 250
IBAT (mA)
4079 G03
Battery Quiescent Current
vs Temperature
0.20
VBAT = 8.4V
CHARGING TERMINATED
OR SHUTDOWN
0.15
0.10
0.05
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
4079 G06
Battery Quiescent Current
vs Battery Voltage
60
50
STANDBY
40 (CHARGING TERMINATED)
30
20
10
SHUTDOWN (EN = 0)
0
0 10 20 30 40 50 60
VBAT (V)
4079 G07
Battery Charge Current
vs Battery Voltage
120
VFB(CHG) = 8.4V
100
RPROG = 3k
80
60
40
20
0
0
RPROG = 30k
246
VBAT (V)
8 10
4079 G08
For more information www.linear.com/LTC4079
Battery Charge Current
vs Temperature
300 VIN = 12V
VBAT = 8.4V
250
ONSET OF THERMAL
REGULATION
RPROG = 1.2k
200
150
100 RPROG = 3k
50
0
–50 –25
RPROG = 30k
0 25 50 75 100 125 150
TEMPERATURE (°C)
4079 G09
4079f
5
5 Page 
LTC4079
Operation
The PROG pin also provides a voltage signal proportional
to the battery charge current. Therefore, the instantaneous
battery current can be determined as follows by monitoring
the PROG pin voltage:
IBAT
=
250 • VPROG
RPROG
Minimize the parasitic capacitance while monitoring the
PROG pin voltage as any capacitance on this pin forms a
pole that may cause instability in the charge control loop.
Undervoltage Detection
An internal undervoltage lockout circuit monitors the VIN
voltage and disables the battery charging circuit until VIN
rises above the undervoltage lockout threshold, 2.55V
(typically). The UVLO threshold has built-in hysteresis
of 140mV. Furthermore, the differential UVLO circuit
also keeps the charger in a low quiescent current mode
by disabling the battery charging circuits when VIN falls
below VBAT by more than 65mV. The differential UVLO
has hysteresis of 80mV, with turn-on at VIN-VBAT = 15mV
(typical).
Battery Temperature Qualified Charging
During battery charging, the battery temperature is sensed
by sampling the voltage on the NTC pin every 3 seconds.
Connect a low drift bias resistor from the NTCBIAS output
to the NTC input and a negative temperature coefficient
(NTC) thermistor, close to the battery pack, from the NTC
pin to ground, as shown in Figure 4. The bias resistor should
be equal to the value of the chosen thermistor at 25°C.
The LTC4079 pauses charging and the charge timer when
the NTC pin voltage indicates that the thermistor resistance
has dropped to 0.576 times its room temperature value.
For a Vishay curve 2 thermistor, this corresponds to 40°C.
Charging is also paused when the thermistor resistance
increases to 2.816 times the room temperature value. For
a Vishay curve 2 thermistor, this increase corresponds
to 0°C.
The hot and cold trip points can be adjusted using a
different type of thermistor, or a different RBIAS resistor,
or by adding a desensitizing resistor in series with the
thermistor, or by a combination of these measures.
LTC4079
NTC SAMPLE
PULSE
BAT
INTERNAL SUPPLY
TOO COLD
TOO HOT
IGNORE NTC
+
–
+
–
+
–
NTCBIAS
NTC
RBIAS
73.8% VNTCBIAS
36.6% VNTCBIAS
0.1V
RNTC
+
T
4079 F04
Figure 4. Battery Temperature Sensing Using NTC Thermistor
Charging resumes when the battery temperature returns to
the normal range and the timer continues from the point
where it was paused.
Input Voltage Regulation
The LTC4079 can regulate a constant voltage on the IN pin
when charging from a current-limited power source such
as a weak battery or a solar panel. This feature can be used
to prevent the input voltage from collapsing below UVLO,
or to maintain the input source voltage at peak power.
The charge current is reduced as the input voltage falls to
the threshold set by an external resistor divider from the
input power source to the EN pin and GND, as shown in
Figure 5. The input voltage regulation threshold, VIN(REG)
is calculated as follows:
VIN(REG)
=
1.190V
•
1+
REN1
REN2
This regulation mechanism allows the charge current to be
selected based on battery requirement and the maximum
power available from the charging source. The LTC4079
automatically reduces the charge current when the input
source cannot provide the programmed charge current.
When input voltage regulation is not needed, connect the
EN pin to the input power source or a digital enable signal.
4079f
For more information www.linear.com/LTC4079
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC4079.PDF ] | |
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