Datasheet
15
LTC4011
4011fa
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 pre-
vents the ON resistance of the internal NFET between 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 is recom-
mended for rejecting PWM switching noise. The value of
C1 should be chosen to yield a 1st order lowpass fre-
quency of less than 500Hz. In the case of a single cell, the
external application circuit shown in Figure 4 is recom-
mended to provide the necessary noise filtering and miss-
ing battery detection.
Thermistor Network Design
The network for proper temperature sensing using a
thermistor with a negative temperature coefficient (NTC)
is shown in Figure 5. R3 is only present for thermistors
with an exponential temperature coefficient (β) above
3750. For thermistors with β below 3750, replace R3 with
a short.
APPLICATIO S I FOR ATIO
WUUU
Table 2. LTC4011 Charging Parameters
CHEM BAT
STATE PIN CHEMISTRY TIMER T
MIN
T
MAX
I
CHRG
TERMINATION CONDITION
PC Both t
MAX
/12 5°C45°CI
PROG
/5 Timer Expires
FC Open NiCd t
MAX
5°C60°CI
PROG
–20mV per Cell or 2°C/Minute
GND NiMH t
MAX
5°C60°CI
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°C60°CI
PROG
/10 Timer Expires
AR Both 5°C45°C0V
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
FAST CHARGE TOP-OFF
TYPICAL FAST PRECHARGE LIMIT VOLTAGE STABILIZATION FAST CHARGE LIMIT CHARGE
R
TIMER
CHARGE RATE (MINUTES) (MINUTES) (HOURS) (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
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