Datasheet

LTC4010
15
4010fb
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:
R
t Hours
TIMER
MAX
= Ω
( )
( )
•
–
30 10
6
Some typical timing values are detailed in Table 3. R
TIMER
should not be less than 15k. The actual time limits used
by the LTC4010 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 LTC4010.
applicaTions inForMaTion
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
Figure 3. Multiple Cell Voltage Divider
10
7
BAT
LTC4010 R2
+
FOR TWO OR
MORE SERIES CELLS
R1 C1
R2 = R1(n – 1)
4010 F03
V
CDIV
GND
6
4
V
CELL
Table 2. LTC4010 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. LTC4010 Time Limit Programming Examples
R
TIMER
TYPICAL FAST
CHARGE RATE
PRECHARGE LIMIT
(MINUTES)
FAST CHARGE
VOLTAGE 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