LTC4000-1 Datasheet, PDF (19/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging with Maximum Power Point Control

LTC4000-1
Applications Information
where R_CS is the charge current sense resistor connected
between the CSP and the CSN pins.
When the voltage at BFB is higher than the recharge
threshold (97.6% of float), the C/X comparator is enabled.
In order to ensure proper C/X termination coming out of
a paused charging condition, connect a capacitor on the
CX pin according to the following formula:
C_CX = 100C_BGATE
where C_BGATE is the total capacitance connected to the
BGATE pin.
For example, a typical capacitance of 1nF requires a capaci-
tor greater than 100nF connected to the CX pin to ensure
proper C/X termination behavior.
If a capacitor is connected to the TMR pin, as soon as the
constant voltage charging is achieved, a charge termina-
tion timer is started. When the charge termination timer
expires, the charge cycle terminates. The total charge
termination time can be programmed according to the
following formula:
C_TMR(nF) = t_TERMINATE(h) • 34.6
If the TMR pin is grounded, charging never terminates and
the battery voltage is held at the float voltage. Note that
regardless of which termination behavior is selected, the
CHRG and FLT pins will both assume a high impedance
state as soon as the charge current falls below the pro-
grammed C/X level.
After the charger terminates, the LTC4000-1 automatically
restarts another charge cycle if the battery feedback voltage
drops below 97.1% of the programmed final float voltage
(V_RECHRG(FALL)). When charging restarts, the CHRG pin
pulls low and the FLT pin remains high impedance.
Output Voltage Regulation Programming
The output voltage regulation level is determined using
the following formula:
R_OFB1
=


V_OUT
1.193
−
1^{}
•
R_OFB2
As in the battery float voltage calculation, when higher
accuracy is important, a slightly more accurate output is
determined using the following formula:
V_OUT
=


R_OFB1
+
R_OFB2
 ^R_OFB2
•
1.193V


–


R_OFB1
 ^R_OFB2

• V_FBG 

where V_FBG is the voltage at the FBG pin during output
voltage regulation, which accounts for all the current from
all resistor dividers that are connected to this pin.
Battery Instant-On and Ideal Diode External PMOS
Consideration
The instant-on voltage level is determined using the fol-
lowing formula:
V_{OUT(INST _ ON)}
=
R_OFB1 + R_OFB2
R_OFB2
• 0.974V
Note that R_OFB1 and R_OFB2 are the same resistors that
program the output voltage regulation level. Therefore,
the output voltage regulation level is always 122.5% of
the instant-on voltage level.
During instant-on operation, it is critical to consider the
charging PMOS power dissipation. When the battery volt-
age is below the low battery threshold (V_LOBAT), the power
dissipation in the PMOS can be calculated as follows:
P_TRKL = _[0.86 • V_FLOAT – V_{BAT ]} • I_CLIM(TRKL)
where I_CLIM(TRKL) is the trickle charge current limit.
On the other hand, when the battery voltage is above the
low battery threshold but still below the instant-on thresh-
old, the power dissipation can be calculated as follows:
P_{INST _ ON} = _[0.86 • V_FLOAT – V_{BAT ]} • I_CLIM
where I_CLIM is the full scale charge current limit.
For example, when charging a 3-cell Lithium Ion battery
with a programmed full charged current of 1A, the float
voltage is 12.6V, the bad battery voltage level is 8.55V and
the instant-on voltage level is 10.8V. During instant-on
operation and in the trickle charge mode, the worst case
40001f
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