LTC4011_15 Datasheet, PDF (16/26 Pages) Linear Technology – High Efficiency Standalone Nickel Battery Charger

LTC4011
Applications Information
Table 2. LTC4011 Charging Parameters
STATE
CHEM
BAT
PIN
CHEMISTRY TIMER T_MIN T_MAX I_CHRG
TERMINATION CONDITION
PC
Both
t_MAX/12 5°C 45°C I_PROG/5 Timer Expires
FC
Open
NiCd
t_MAX
5°C 60°C I_PROG –20mV per Cell or 2°C/Minute
GND
NiMH
t_MAX
5°C 60°C I_PROG 1.5°C/Minute for First t_MAX/12 Minutes if Initial
V_CELL < 1.325V
–10mV per Cell or 1°C/Minute After t_MAX/12 Minutes
or if Initial V_CELL > 1.325V
TOC
GND
NiMH
t_MAX/3 5°C 60°C I_PROG/10 Timer Expires
AR
Both
5°C 45°C
0
V_CELL < 1.325V
PC: Precharge
FC: Fast Charge (Initial –∆V Termination Hold Off of t_MAX/12 Minutes May Apply)
TOC: Top-Off Charge (Only for NiMH ∆T/∆t FC Termination After Initial t_MAX/12 Period)
AR: Automatic Recharge (Temperature Limits Apply to State Termination Only)
Table 3. LTC4011 Time Limit Programming Examples
R_TIMER
24.9k
TYPICAL FAST
CHARGE RATE
2C
PRECHARGE LIMIT
(MINUTES)
3.8
FAST CHARGE
VOLTAGE STABILIZATION
(MINUTES)
3.8
33.2k
1.5C
5
5
49.9k
1C
7.5
7.5
66.5k
0.75C
10
10
100k
C/2
15
15
FAST CHARGE LIMIT
(HOURS)
0.75
1
1.5
2
3
TOP-OFF
CHARGE
(MINUTES)
15
20
30
40
60
Programming Maximum Charge Times
Connecting the appropriate resistor between the TIMER
pin and GND programs the maximum duration of various
charging states. To some degree, the value should reflect
how closely the programmed charge current matches the
1C rate of targeted battery packs. The maximum fast charge
period is determined by the following equation:
Some typical timing values are detailed in Table 3. R_TIMER
should not be less than 15k. The actual time limits used
by the LTC4011 have a resolution of approximately ±30
seconds in addition to the tolerances given the Electrical
Characteristics table. If the timer ends without a valid –∆V or
∆T/∆t charge termination, the charger enters the fault state.
The maximum time period is approximately 4.3 hours.
Cell Voltage Network Design
An external resistor network is required to provide the
average single-cell voltage to the V_CELL pin of the LTC4011.
16
The proper circuit for multicell packs is shown in Figure 3.
The ratio of R2 to R1 should be a factor of (n – 1), where
n is the number of series cells in the battery pack. The
value of R1 should be between 1k and 100k. This range
limits the sensing error caused by V_CELL leakage current
and prevents the ON resistance of the internal NFET be-
tween V_CDIV and GND from causing a significant error in
the V_CELL voltage. The external resistor network is also
used to detect battery insertion and removal. The filter
formed by C1 and the parallel combination of R1 and R2
BAT 12
LTC4011
V_CELL 8
FOR TWO OR
MORE SERIES CELLS
+
R2
V_CDIV
9
GND
5
4011 F03
R1
C1
R2 = R1(n – 1)
Figure 3. Mulitple Cell Voltage Divider
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