LTC4000_15 Datasheet, PDF (26/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging and Power Management

LTC4000
Applications Information
Design Example
In this design example, the LTC4000 is paired with the
LT3845A buck converter to create a 10A, 3-cell LiFePO₄
battery charger. The circuit is shown on the front page
and is repeated here in Figure 14.
• The input voltage monitor falling threshold is set at
14.3V according to the following formula:
R_VM1
=


14.3V
1.193V
−
1^{}
•
100kΩ
≈
1.10MΩ
• The IL pin is left open such that the voltage on this pin
is >1.05V. The regulation voltage on the IIMON pin is
clamped at 1.0V with an accurate internal reference.
Therefore, the input current limit is set at 10A according
to the following formula:
R_IS
=
0.050V
10A
=
5mΩ
• R_CL is set at 24.9kΩ such that the voltage at the CL pin
is 1.25V. Similar to the IIMON pin, the regulation voltage
on the IBMON pin is clamped at 1V with an accurate
internal reference. Therefore, the charge current limit
is set at 10A according to the following formula:
I_{CLIM(MAX )}
=
0.050V
R_CS
=
0.050V
5mΩ
=
10A
• The trickle charge current level is consequently set at
1.25A, according to the following formula:
I_{CLIM( TRKL )}
=
0.25µA
•
24.9kΩ
5mΩ
=
1.25A
• The battery float voltage is set at 10.8V according to
the following formula:
R_BFB1
=


10.8
1.136
−
1^{}
•
133kΩ
≈
1.13MΩ
• The bad battery detection time is set at 43 minutes
according to the following formula:
C_TMR (nF)
=
t_BADBAT (h)
•
138.5
=
43
60
•
138.5
=
100nF
15V TO 60V
5mΩ
LT3845A
IN
SHDN
V_C
OUT
100µF
Si7135DP
14.7k
1.10M
ITH
RST
CLN
IN
1µF
VM
100k
3.0V
ENC
CHRG
FLT
IIMON
10nF
IBMON
10nF
TMR
47nF
CC
10M
IID IGATE CSP
CSN
BGATE
BAT
OFB
LTC4000
FBG
IL CL
BFB
NTC
CX
GND BIAS
22.1k 22.1k
0.1µF
1µF
12V, 15A
1.15M 5mΩ
Si7135DP
127k
133k
1.13M
10.8V FLOAT
10A MAX CHARGE
CURRENT
10k
10k
3-CELL Li-Ion
BATTERY PACK
NTHS0603
N02N1002J
4000 F14
Figure 14. 48V to 10.8V at 10A Buck Converter Charger for Three LiFePO₄ Cells
26
For more information www.linear.com/LTC4000
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