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PDF LTC4007 Data sheet ( Hoja de datos )
| Número de pieza | LTC4007 | |
| Descripción | Standalone Li Battery Charger | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC4007
4A, High Efficiency,
Standalone Li-Ion Battery Charger
FEATURES
DESCRIPTION
n Complete Charger Controller for 3- or 4-Cell
Lithium-Ion Batteries
n High Conversion Efficiency: Up to 96%
n Output Currents Exceeding 4A
n ±0.8% Charging Voltage Accuracy
n Built-In Charge Termination for Li-Ion Batteries
n AC Adapter Current Limiting Maximizes Charge Rate*
n Thermistor Input for Temperature Qualified Charging
n Wide Input Voltage Range: 6V to 28V
n 0.5V Dropout Voltage; Maximum Duty Cycle: 98%
n Programmable Charge Current: ±4% Accuracy
n Indicator Outputs for Charging, C/10 Current Detection,
AC Adapter Present, Low Battery, Input Current
Limiting and Faults
n Charging Current Monitor Output
n Available in a 24-Pin Narrow SSOP Package
APPLICATIONS
n Notebook Computers
n Portable Instruments
n Battery-Backup Systems
n Standalone Li-Ion Chargers
The LTC®4007 is a complete constant-current/constant-
voltage charger controller for 3- or 4-cell lithium-ion batteries.
The PWM controller uses a synchronous, quasi-constant
frequency, constant off-time architecture that will not
generate audible noise even when using ceramic capacitors.
Charging current is programmable to ±4% accuracy using
a programming resistor. Charging current can also be
monitored as a voltage across the programming resistor.
The output float voltage is pin programmed for cell count
(3 cells or 4 cells) and chemistry (4.2V/4.1V). A timer,
programmed by an external resistor, sets the charge
termination time. Charging is automatically restarted when
cell voltage falls below 3.9V/cell.
LTC4007 includes a thermistor input, which suspends
charging if an unsafe temperature condition is detected.
If the cell voltage is less than 2.5V, a low-battery indicator
asserts and can be used to program a trickle charge current
to safely charge depleted batteries. The FAULT pin is also
asserted and charging terminates if the low-battery con-
dition persists for more than 1/4 of the total charge time.
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.
Protected by U.S. Patents including 5723970.
TYPICAL APPLICATION
12.6V, 4A Li-Ion Battery Charger
DCIN
0V TO 28V
VLOGIC
LOBAT
ICL
ACP
SHDN
FAULT
CHG
FLAG
100k
THERMISTOR
10k
NTC
100k 100k
32.4k
0.47μF
3C4C
DCIN
CHEM
LOBAT
INFET
CLP
ICL LTC4007 CLN
ACP TGATE
SHDN
FAULT
CHG
FLAG
BGATE
PGND
CSP
BAT
NTC PROG
RT ITH
GND
309k
TIMING RESISTOR
(~2 HOURS)
INPUT SWITCH
0.1μF
4.99k
15nF 0.025Ω
20μF
Q1 10μH 0.025Ω
Q2
SYSTEM
LOAD
Li-Ion
20μF BATTERY
3.01k
3.01k
6.04k
0.0047μF
0.12μF
26.7k
Q1: Si4431DY
Q2: FDC6459
CHARGING
CURRENT
MONITOR
4007 TA01
4007fc
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC4007
INFET Response Time to
Reverse Current
Vgs = 0
Vgs OF PFET (2V/DIV)
Vs OF PFET (5V/DIV)
Vs = 0V
Id (REVERSE) OF
PFET (5A/DIV)
Id = 0A
1.25μs/DIV
TEST PERFORMED ON DEMOBOARD
VIN = 15VDC
CHARGER = ON
VCHARGE = 12.6V
PFET = 1/2 Si4925DY
ICHARGE = <10mA
4007 G01
PWM Frequency vs Duty Cycle
350
300
250
200
Line Regulation
0.10
0.05
0
–0.05
–0.10
C3C4 = OPEN
–0.15
–0.20
–0.25
C3C4 = GND
–0.30
–0.35
–0.40
–0.45
13 15 17 19 21 23 25 27 29 31
VDCIN (V)
4007 G02
Disconnect/Reconnect Battery
(Load Dump)
VFLOAT
1V/DIV
3A STEP
1A STEP
1A STEP
VOUT vs IOUT
0
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
–4.0
–4.5
–5.0
0
3C4C = GND
3C4C = OPEN
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
OUTPUT CURRENT (A)
4007 G03
1A Load Step (Battery Present)
CHARGER CURRENT (1A/DIV)
150
PROGRAMMED CURRENT = 10%
100
50 DCIN = 15V
DCIN = 20V
0 DCIN = 24V
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
DUTY CYCLE (VOUT/VIN)
4007 G04
LOAD
STATE
3A STEP
DISCONNECT
RECONNECT
LOAD CURRENT = 1A, 2A, 3A
DCIN = 20V
VFLOAT = 12.6V (3C4C = GND, CHEM = OPEN)
4007 G05
OUTPUT VOLTAGE (500mV/DIV)
DCIN = 20V
VFLOAT = 12.6V
4007 G06
1A Load Step
(Battery Not Present)
CHARGER CURRENT (500mA/DIV)
OUTPUT VOLTAGE (5V/DIV)
DCIN = 20V
VFLOAT = 12.6V
4007 G07
Battery Leakage Current
vs Battery Voltage
40
VDCIN = 0V
35
30
25
20
15
10
5
0
0 5 10 15 20 25 30
BATTERY VOLTAGE (V)
4007 G08
4007fc
5
5 Page 
LTC4007
OPERATION
The peak inductor current, at which ICMP resets the SR
latch, is controlled by the voltage on ITH. ITH is in turn
controlled by several loops, depending upon the situation
at hand. The average current control loop converts the
voltage between CSP and BAT to a representative cur-
rent. Error amp CA2 compares this current against the
desired current programmed by RPROG at the PROG pin
and adjusts ITH until:
VREF = VCSP – VBAT + 11.67μA • 3.01kΩ
RPROG
3.01kΩ
therefore,
ICHARGE(MAX)
= ⎛⎝⎜RVPRREOFG
–
⎞
11.67μA⎟ •
⎠
3.01kΩ
RSENSE
The voltage at BAT is divided down by an internal resis-
tor divider and is used by error amp EA to decrease ITH
if the divider voltage is above the 1.19V reference. When
the charging current begins to decrease, the voltage at
PROG will decrease in direct proportion. The voltage at
PROG is then given by:
VPROG
=
(ICHARGE
•
RSENSE
+
11.67μA
•
3.01kΩ)
•
RPROG
3.01kΩ
VPROG is plotted in Figure 2.
The amplifier CL1 monitors and limits the input current,
normally from the AC adapter to a preset level (100mV/RCL).
At input current limit, CL1 will decrease the ITH voltage,
1.2 1.19V
1.0
0.8
0.6
0.4
0.309V
0.2
0
0 20 40 60 80 100
ICHARGE (% OF MAXIMUM CURRENT)
4007 F02
Figure 2. VPROG vs ICHARGE
thereby reducing charging current. The ICL indicator output
will go low when this condition is detected and the FLAG
indicator will be inhibited if it is not already LOW.
If the charging current decreases below 10% to 15%
of programmed current while engaged in input current
limiting, BGATE will be forced low to prevent the charger
from discharging the battery. Audible noise can occur in
this mode of operation.
An overvoltage comparator guards against voltage tran-
sient overshoots (>7% of programmed value). In this
case, both MOSFETs are turned off until the overvoltage
condition is cleared. This feature is useful for batteries
which “load dump” themselves by opening their protection
switch to perform functions such as calibration or pulse
mode charging.
PWM Watchdog Timer
There is a watchdog timer that observes the activity on
the BGATE and TGATE pins. If TGATE stops switching for
more than 40μs, the watchdog activates and turns off the
top MOSFET for about 400ns. The watchdog engages to
prevent very low frequency operation in dropout—a po-
tential source of audible noise when using ceramic input
and output capacitors.
Charger Start-Up
When the charger is enabled, it will not begin switching
until the ITH voltage exceeds a threshold that assures initial
current will be positive. This threshold is 5% to 15% of the
maximum programmed current. After the charger begins
switching, the various loops will control the current at a
level that is higher or lower than the initial current. The
duration of this transient condition depends upon the loop
compensation, but is typically less than 100μs.
Thermistor Detection
The thermistor detection circuit is shown in Figure 3. It
requires an external resistor and capacitor in order to
function properly.
The thermistor detector performs a sample-and-hold
function. An internal clock, whose frequency is determined
4007fc
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC4007.PDF ] | |
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