Datasheet

LTC4011
16
4011fb
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.
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
12
9
BAT
LTC4011 R2
+
FOR TWO OR
MORE SERIES CELLS
R1 C1
R2 = R1(n – 1)
4011 F03
V
CDIV
GND
8
5
V
CELL
Figure 3. Mulitple Cell Voltage Divider
applicaTions inForMaTion
Table 2. LTC4011 Charging Parameters
STATE
CHEM
PIN
BAT
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
TYPICAL FAST
CHARGE RATE
PRECHARGE LIMIT
(MINUTES)
FAST
CHARGE
VOLT
AGE STABILIZATION
(MINUTES)
FAST
CHARGE LIMIT
(HOURS)
TOP-OFF
CHARGE
(MINUTES)
24.9k 2C 3.8 3.8 0.75 15
33.2k 1.5C 5 5 1 20
49.9k 1C 7.5 7.5 1.5 30
66.5k 0.75C 10 10 2 40
100k C/2 15 15 3 60