LTC4000_15 Datasheet, PDF (27/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging and Power Management

LTC4000
Applications Information
• The charge termination time is set at 2.9 hours accord-
ing to the following formula:
C_TMR(nF) = t_TERMINATE(h) • 34.6 = 2.9 • 34.6 = 100nF
• The C/X current termination level is programmed at 1A
according to the following formula:
R_CX
=
(^1A
•
5mΩ₎ + 0.5mV
0.25µA
≈
22.1kΩ
Note that in this particular solution, the timer termina-
tion is selected since a capacitor connects to the TMR
pin. Therefore, this C/X current termination level only
applies to the CHRG indicator pin.
• The output voltage regulation level is set at 12V accord-
ing to the following formula:
R_OFB1
=


12
1.193
−
1^{}
•
127kΩ
≈
1.15MΩ
• The instant-on voltage level is consequently set at 9.79V
according to the following formula:
V_INST
_
ON
=
1150kΩ + 127kΩ
127kΩ
•
0.974V
=
9.79V
The worst-case power dissipation during instant-on
operation can be calculated as follows:
• During trickle charging:
P_TRKL = 0.86 • V_FLOAT – V_BAT  • I_{CLIM _ TRKL}
= [0.86 • 10.8] • 1A

= 9.3W
• And beyond trickle charging:
P_{INST _ ON} = 0.86 • V_FLOAT – V_BAT  • I_CLIM
= [0.86 • 10.8 – 7.33] • 10A

= 19.3W
Therefore, depending on the layout and heat sink avail-
able to the charging PMOS, the suggested PMOS over
temperature detection circuit included in Figure 7 may
need to be included. For the complete application circuit,
please refer to Figure 25.
• The range of valid temperature for charging is set at
–1.5°C to 41.5°C by picking a 10k Vishay Curve 2 NTC
thermistor that is thermally coupled to the battery, and
connecting this in series with a regular 10k resistor to
the BIAS pin.
• For compensation, the procedure described in the
empirical loop compensation section is followed. As
recommended, first a 1µF C_C and 10k R_C is used, which
sets all the loops to be stable. For an example of typical
transient responses, the charge current regulation loop
when V_OFB is regulated to V_{OUT(INST_ON)} is used here.
Figure 15 shows the recommended setup to inject a
DC-coupled charge current variation into this particular
loop. The input to the CL pin is a square wave at 70Hz
with the low level set at 120mV and the high level set
at 130mV, corresponding to a 1.2A and 1.3A charge
current (100mA charge current step). Therefore, in this
particular example the trickle charge current regulation
stability is examined. Note that the nominal trickle
charge current in this example is programmed at 1.25A
(R_CL = 24.9kΩ).
BA
10k
1500pF
1k
0.015µF
IBMON
LTC4000
CL
SQUARE WAVE
GENERATOR
f = 60Hz
4000 F15
Figure 15. Charge Current Regulation Loop Compensation Setup
For more information www.linear.com/LTC4000
4000fb
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