Datasheet

17
LTC4060
4060f
Trickle Charge
The trickle charge function is normally not required due to
the automatic recharge feature. However, the LTC4060
does provide a modest pull-up current (I
BRD
) as part of its
battery removal detection method. If additional current is
required for trickle charge or to support battery removal
detection with current loads greater than I
BRD
, then the
simple circuit of Figure 4 will facilitate that. The diode
insures no reverse discharge current when V
IN
is removed
and the resistor sets the trickle current.
Extending Charge Current
Extending the charge current beyond 2A can be accom-
plished by paralleling an external current sense resistor,
R
ISET,
with the internal current sense resistor as shown in
Figure 5. Bond wire, lead frame and PCB interconnect
resistance and mismatches in the two sense resistor’s
value will cause charge current variability to increase in
proportion to the extension in current. Resistor R
ISET
should be connected directly to the LTC4060 to reduce
errors. The total current sense resistor, bond wire and lead
frame resistance is approximately 0.08Ω (T.C. ≅ 3500ppm/
°C). The formula for extended fast charge current is:
II
R
AA
MAX EXT MAX
ISET
()
•
.
•.
=+
⎛
⎝
⎜
⎞
⎠
⎟
==
1
008
2153
for R
ISET
= 0.16Ω and R
PROG
= 698Ω.
Adequate PNP beta is required to meet the DRIVE pin
capability and the increased PNP power dissipation will
require additional heat sinking.
TYPICAL APPLICATIO S
U
V
CC
V
IN
1N4001
LTC4060
SENSE
DRIVE
BAT
4060 F04
2-CELL
NiMH
BATTERY
3.3k
3
14
1
2
+
V
CC
V
IN
LTC4060
SENSE
DRIVE
BAT
4060 F05
2-CELL
NiMH
BATTERY
R
ISET
0.16Ω
0.08Ω
3
14
1
2
+
Figure 4. Adding Trickle Charge
Figure 5. Extended Charge Current Operation