LTC4006 Linear Technology, LTC4006 Datasheet - Page 10

• Manufacturer Part Number: LTC4006
• Description: Standalone Li-Ion Battery Charger
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC4006
Charger Current Programming
The basic formula for charging current is:
Table 2. Recommended R
Setting the Timer Resistor
The charger termination timer is designed for a range of
1hour to 3 hour with a 15% uncertainty. The timer is
programmed by the resistor R
equation:
It is important to keep the parasitic capacitance on the R
pin to a minimum. The trace connecting R
be as short as possible.
CHG Status Output Pin
When the charge cycle starts, the CHG pin is pulled down
to ground by an internal N-channel MOSFET that can drive
more than 100 A. When the charge current drops to 10%
of the full-scale current (C/10), the N-channel MOSFET is
turned off and a weak 25 A current source to ground is
connected to the CHG pin. After a time out occurs, the pin
will go into a high impedance state. By using two different
value pull-up resistors, a microprocessor can detect three
states from this pin (charging, C/10 and stop charging).
See Figure 6.
Battery Detection
It is generally not good practice to connect a battery while
the charger is running. The timer is in an unknown state
and the charger could provide a large surge current into
the battery for a brief time. The circuit shown in Figure 7
keeps the charger shut down and the timer reset while a
battery is not connected.
10
t
I
CHARGE MAX
TIMER
I
MAX
1.0
2.0
3.0
4.0
= 2
(A)
(
27
• R
)
RT
100
R
U
SENSE
• 175pF (Refer to Figure 5)
R
SENSE
mV
SENSE
U
0.100
0.050
0.033
0.025
Resistor Values
( ) 1%
RT
W
using the following
T
R
to R
SENSE
0.25
0.25
0.5
0.5
U
RT
(W)
should
T
Alternatively, a normally closed switch can be used to
detect when the battery is present (see Figure 8).
BATTERY CONNECTED
SWITCH CLOSED IF
BATTERY CONNECTED
SWITCH OPEN WHEN
ADAPTER
120
200
180
160
140
100
POWER
80
60
40
20
0
100
Figure 6. Microprocessor Interface
ADAPTER
POWER
LTC4006
150
Figure 5. t
CHG
200
250
3.3V
Figure 7
Figure 8
470k
R
RT
200k
300 350
TIMER
(k )
33k
vs R
DCIN
ACP/SHDN
400 450 500
OUT
IN
RT
LTC4006
DCIN
ACP/SHDN
V
DD
P
4006 F05
4006 F06
LTC4006
4006 F08
sn4006 4006is
4006 F07