LTC4060_15 Datasheet, PDF (10/20 Pages) Linear Technology – Standalone Linear NiMH/NiCd Fast Battery Charger

LTC4060
U
OPERATIO
applied to the SHDN pin, shutdown ends and charge quali-
fication is entered.
Charge Qualification
After exiting the sleep or shutdown modes the LTC4060
will check for the presence of a battery and for proper
battery temperature (if a thermistor is used) before initiat-
ing charging.
When V_CELL (V_BAT/Number of Cells) is below 2.05V (V_BR),
a battery is assumed to be present. Should V_CELL rise
above 1.95V (V_BOV) for a time greater than the battery
overvoltage event delay shown in the far right column of
Table 1, then a battery overvoltage condition is detected
and charging stops. Once stopped in this way, qualifica-
tion can be reinitiated after V_CELL has fallen below 1.9V
(V_BOV – V_BOVH) only by removing and replacing the battery
(or replacing the battery if the overvoltage condition is a
result of battery removal), toggling the SHDN pin low to
high or removing and reapplying power to the charger.
If the NTC pin voltage is above the temperature disable
threshold (V_NDIS), the LTC4060 verifies that the ther-
mistor temperature is between 5°C and 45°C. Charging
will not initiate until these temperature limits are met.
The LTC4060 continues to qualify important voltage and
temperature parameters during all charging states. If V_CC
drops below the undervoltage lockout threshold, sleep
mode is entered.
If the internal die temperature becomes excessive, charg-
ing stops and the part enters the shutdown state. Once in
the shutdown state charge qualification can be reinitiated
only when the die temperature drops to normal and then
by removing and replacing the battery or toggling the
SHDN pin low to high or removing and reapplying power
to the charger.
Precharge
The state that is entered when qualified charging begins is
precharge. The CHRG status output is set low and remains
low during both precharge and fast charge. If the voltage
on V_CELL is below the 900mV (V_FCQ) fast charge qualifica-
tion voltage, the LTC4060 charges using one-fifth the
maximum programmed charge current. The cell voltage is
continuously checked to determine when the battery is
ready to accept a fast charge. Until this voltage reaches
V_FCQ, the LTC4060 remains in precharge.
If an external thermistor indicates that the sensed tem-
perature is beyond a range of 5°C to 45°C charging is
suspended, the charge timer is paused and the CHRG
status output remains low. Normal charging resumes
from the previous state when the sensed temperature
rises above 5°C or falls below 45°C.
Fast Charge
When the average cell voltage exceeds V_FCQ, the LTC4060
transitions from the precharge to the fast charge state and
Table 1. LTC4060 Time Limit Programming Examples
FAST
CHARGE
CURRENT
2A
R_PROG
698Ω
C_TIMER
1nF
TYPICAL
FAST
CHARGE
RATE
(C)
1.5
BATTERY
VOLTAGE
STABILIZATION
HOLD OFF
(MINUTES)
4.6 to 5.7
2A
698Ω 1.5nF
1
6.9 to 8.4
2A
698Ω 1.8nF
0.75
8.4 to 10.3
2A
698Ω 2.7nF
0.5
12.6 to 15.4
400mA 3480Ω 180pF
1.5
4.2 to 5.2
400mA 3480Ω 270pF
1
6.3 to 7.7
400mA 3480Ω 390pF
0.75
8.9 to 11
400mA 3480Ω 560pF
0.5
12.6 to 15.4
CHARGE
TIME
LIMIT
(t_MAX)
(HOURS)
1.1
1.6
2
3
1
1.5
2.1
3
BATTERY
VOLTAGE
SAMPLING
INTERVAL
(SECONDS)
15
23
28
42
14
21
30
42
AUTOMATIC
RECHARGE
ENTRY
DELAY
(SECONDS)
15 to 31
23 to 46
28 to 56
42 to 84
14 to 28
21 to 42
30 to 60
42 to 84
UVLO EXIT, BATTERY
INSERTION/REMOVAL/OVERVOLTAGE,
FAST CHARGE ENTRY AND
THERMISTOR EVENT DELAYS (ms)
175 to 260
260 to 390
320 to 480
480 to 720
160 to 240
240 to 360
340 to 510
480 to 720
4060f
10