LTC4006 Datasheet, PDF (8/16 Pages) Linear Technology – 4A, High Efficiency, Standalone Li-Ion Battery Charger

LTC4006
U
OPERATIO
Table 1. Truth Table for LTC4006 Operation
MODE
DCIN
Shut Down by Low Adapter Voltage
<BAT
Conditioning a Depleted Battery
>BAT
Normal Charging
>BAT
Input Current Limited Charging
Charger Paused Due to Thermistor Out of Range
>BAT
>BAT
Shut Down by ACP/SHDN Pin
Terminated by Low-Battery Fault (Note 1)
>BAT
>BAT
Top-Off Charging. C/10 is Latched
>BAT
Timer is Reset by C/10 Comparator (Latched),
then Terminates After 1/4 T
Terminated by Expired Timer
>BAT
>BAT
Timer Defeated. (Low-Battery Conditioning Still
Functional)
Shut Down by Undervoltage Lockout
Timer Defeated Until V_BAT > 3.9V/Cell
X
>BAT
and <UVL
>BAT
BAT VOLTAGE
>UVLO
<2.5V/Cell
>2.5V/Cell
>2.5V/Cell
X
BAT CURRENT
Leakage
10% Programmed
Current
Programmed
Current
Unknown
OFF
X
OFF
<2.5V/Cell
OFF
V_FLOAT
OFF
V_FLOAT
OFF
V_FLOAT**
OFF
X
X
<UVL
OFF
2.5V ≤ V_BAT ≤3.9V Programmed
(V/Cell)
Current
ACP/SHDN
LOW
HIGH
HIGH
HIGH
HIGH
Forced LOW
HIGH
HIGH
HIGH
HIGH
X
HIGH
HIGH
TIMER STATE
Reset
Running
Running
Running
Paused
Reset
>T/4 Stopped
<T/4 After C/10
Comparator Trip.
Running
>T/4 After C/10
Comparator Trip.
Stopped
>T Stopped
X
Reset
Running
CHG*
HIGH
LOW
LOW
LOW
LOW
(Faulted)
HIGH
HIGH
(Faulted)
25µA
HIGH
(Waiting
for Restart)
HIGH
(Waiting
for Restart)
Forced LOW
HIGH**
LOW
*Open Drain. High when used with pull-up resistor.
**Most probable condition, X = Don’t care
Note 1: If a depleted battery is inserted while the charger is in this state,
the charger must be reset to initiate charging.
therefore,
I_CHARGE
=


V_REF
R_IMON
–
11.67µA^{}
•
3kΩ
R_SENSE
The voltage at BAT is divided down by an internal resistor
divider and is used by error amp EA to decrease I_TH if the
divider voltage is above the 1.19V reference. When the
charging current begins to decrease, the voltage at I_MON
will decrease in direct proportion. The voltage at I_MON is
then given by:
( ) ^V_IMON ⁼
I_CHARGE •R_SENSE + 11.67µA • 3kΩ
• ^RIMON
3kΩ
V_IMON is plotted in Figure 2.
The amplifier CL1 monitors and limits the input current to
a preset level (100mV/R_CL). At input current limit, CL1 will
decrease the I_TH voltage, thereby reducing charging cur-
rent. When this condition is detected, the C/10 indicator
will be inhibited if it is not already active. 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 protec-
tion switch to perform functions such as calibration or
pulse mode charging.
As the voltage at BAT increases to near the input voltage
at DCIN, the converter will attempt to turn on the top
MOSFET continuously (“dropout’’). A watchdog timer
detects this condition and forces the top MOSFET to turn
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