LTC4060
U
OPERATIO
Battery Chemistry Selection
Insertion and Removal of Batteries
Thedesiredbatterychemistryisselectedbyprogramming
the CHEM pin to the proper voltage. When wired to GND,
a set of parameters specific to charging NiMH cells is
selected. When CHEM is connected to VCC, charging is
optimizedforNiCdcells. Thevariouschargingparameters
are detailed in Table 2.
The LTC4060 automatically senses the insertion or re-
moval of a battery by monitoring the VCELL pin voltage.
Either the charge current, or if not charging then an
internal pull-up current (IBRD), will pull VCELL up when the
battery is removed. When this voltage rises above 2.05V
(VBR) for a time greater than the battery removal event
delayshowninTable1, theLTC4060considersthebattery
to be absent. Inserting a battery, causing VCELL to fall
below both VBR and 1.95V (VBOV) for a period longer than
the battery insertion event delay shown in Table 1, results
in the LTC4060 recognizing a battery present and initiates
a completely new charge cycle beginning with charge
qualification. All battery currents are inhibited while in
shutdown.
Cell Selection
The number of series cells is selected using the SEL0 and
SEL1 pins. For one cell, both pins connect to GND. For two
cells, SEL0 connects to VCC and SEL1 to GND. For three
cells, SEL0 connects to GND and SEL1 to VCC. For four
cells, both connect to VCC.
Table 2. LTC4060 Charging Parameters
STATE
CHEM
Both
CHARGE TIME LIMIT
T
T
I
CHRG
TYPICAL TERMINATION CONDITION
V ≥ 0.9V
CELL
MIN
MAX
Precharge
Fast Charge
t
t
t
5°C
5°C
5°C
45°C
55°C
55°C
I
/5
MAX
MAX
MAX
MAX
NiCd
I
I
–16mV Per Cell After Initial t
/12 Delay
MAX
MAX
MAX
NiMH
–8mV Per Cell After Initial t
/12 Delay
MAX
W U U
U
APPLICATIO S I FOR ATIO
Programming Charge Current
Under precharge conditions, the current is reduced to
20% of the fast charge value (IMAX).The LTC4060 is
designed for a maximum current of 2A. This translates to
a maximum PROG pin current of 2.15mA and a minimum
program resistor of 698Ω. Reduced accuracy at low
current limits the useful fast charge current to a minimum
of approximately 200mA. Errors in the charge current can
be statistically approximated as follows:
The battery charge current is set with an external program
resistor connected from the PROG pin to GND. The for-
mula for the battery fast charge current or IMAX is:
⎛ 1.5V ⎞
⎝RPROG
IMAX = I
• 930 =
• 930
⎟
(
)
⎜
PROG
⎠
or
One Sigma Error ≅ 7mA
1395
IMAX
RPROG
=
For best stability over temperature and time, 1% metal-
filmresistorsarerecommended.CapacitanceonthePROG
pin should be limited to about 75pF to insure adequate AC
phase margin for its amplifier.
where RPROG is the total resistance from the PROG pin to
ground. For example, if 1A of fast charge current is
required:
Different charge currents can be programmed by various
means such as by switching in different program resis-
tors. A voltage DAC connected through a resistor to the
PROG pin or a current DAC connected in parallel with a
1395
1A
RPROG
=
= 1.4k 1% Resistor
4060f
12
Linear Systems [ Linear Systems ]
