LTC4000-1 Datasheet, PDF (30/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging with Maximum Power Point Control

LTC4000-1
Applications Information
Design Example
In this design example, the LTC4000-1 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 22.
• With R_IFB2 set at 20k, the input voltage monitoring falling
threshold is set at 15V and the input voltage regulation
level is set at 17.6V according to the following formulas:
R_VM3
=


1−
1.193V
15V




17.6V
1V


20kΩ
=
324kΩ
R_VM4
=


1.193V


17.6V
15V


−
1^{}
20kΩ
=
8.06kΩ
• The input current sense resistor is set at 5mΩ. There-
fore, the voltage at the IIMON pin is related to the input
current according to the following formula:
V_IIMON = (0.1Ω) • I_RIS
• 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
SOLAR PANEL INPUT
<60V OPEN CIRCUIT VOLTAGE
17.6V PEAK POWER VOLTAGE
5mΩ
BIAS
324k
IN
SHDN
1M
LT3845A
V_C
OUT
100µF
14.7k
47nF
RST
CLN
IN
1µF
ITH
CC
8.06k
VM
3.0V
LTC4000-1
Si7135DP
IID IGATE CSP
CSN
BGATE
BAT
OFB
FBG
IFB
BFB
20k
ENC
CHRG
NTC
FLT _{IIMON IBMON TMR}
CL
CX GND BIAS
10nF
24.9k 22.1k
10nF
0.1µF
BIAS
1µF
1.15M
127k
133k
1.13M
10k
10k
NTHS0603
N02N1002J
V_OUT
12V, 15A
5mΩ
Si7135DP
V_BAT
10.8V FLOAT
10A MAX CHARGE
CURRENT
3-CELL Li-Ion
BATTERY PACK
40001 F22
Figure 22. 10.8V at 10A Charger for Three LiFePO₄ Cells with Solar Panel Input
40001f
30