LTC4060 Linear Integrated, LTC4060 Datasheet - Page 12

• Manufacturer Part Number: LTC4060
• Description: Standalone Linear NiMH/NiCd Fast Battery Charger
• Manufacturer: Linear Integrated

OPERATIO
APPLICATIO S I FOR ATIO
LTC4060
Battery Chemistry Selection
The desired battery chemistry is selected by programming
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 V
optimized for NiCd cells. The various charging parameters
are detailed in Table 2.
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 V
cells, SEL0 connects to GND and SEL1 to V
cells, both connect to V
Table 2. LTC4060 Charging Parameters
12
Programming Charge Current
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 I
where R
ground. For example, if 1A of fast charge current is
required:
or
Fast Charge
Precharge
I
R
MAX
STATE
PROG
R
PROG
PROG
=
=
(
I
PROG
1395
I
=
MAX
is the total resistance from the PROG pin to
CHEM
NiMH
1395
NiCd
Both
1
)
U
A
•
U
930
=
1 4 . 1% Resistor
CC
CHARGE TIME LIMIT
=
U
CC
.
⎛
⎜
⎝
k
R
and SEL1 to GND. For three
1 5
PROG
.
t
t
t
MAX
MAX
MAX
V
W
⎞
⎟
⎠
•
930
CC
, charging is
MAX
CC
U
T
5°C
5°C
5°C
. For four
MIN
is:
T
45°C
55°C
55°C
MAX
Insertion and Removal of Batteries
The LTC4060 automatically senses the insertion or re-
moval of a battery by monitoring the V
Either the charge current, or if not charging then an
internal pull-up current (I
battery is removed. When this voltage rises above 2.05V
(V
delay shown in Table 1, the LTC4060 considers the battery
to be absent. Inserting a battery, causing V
below both V
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.
Under precharge conditions, the current is reduced to
20% of the fast charge value (I
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:
For best stability over temperature and time, 1% metal-
film resistors are recommended. Capacitance on the PROG
pin should be limited to about 75pF to insure adequate AC
phase margin for its amplifier.
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
BR
One Sigma Error ≅ 7mA
I
I
MAX
I
I
CHRG
) for a time greater than the battery removal event
MAX
MAX
/5
TYPICAL TERMINATION CONDITION
V
–16mV Per Cell After Initial t
–8mV Per Cell After Initial t
BR
CELL
and 1.95V (V
≥ 0.9V
BRD
), will pull V
BOV
) for a period longer than
MAX
MAX
MAX
/12 Delay
/12 Delay
).The LTC4060 is
CELL
CELL
up when the
pin voltage.
CELL
to fall
4060f