LTC3789 LINER [Linear Technology], LTC3789 Datasheet - Page 18

• Manufacturer Part Number: LTC3789
• Description: High Voltage High Current Controller for Battery Charging and Power Management
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
LTC4000
Charge Current Limit Setting and Monitoring
The regulated full charge current is set according to the
following formula:
where V
internally pulled up with an accurate current source of
50µA. Therefore, an equivalent formula to obtain the input
current limit is:
The charge current through the sense resistor is available
for monitoring through the IBMON pin. The voltage on
the IBMON pin varies with the current through the sense
resistor as follows:
Similar to the IIMON pin, the regulation voltage level at
the IBMON pin is clamped at 1V with an accurate internal
reference. At 1V on the IBMON pin, the charge current
limit is regulated to the following value:
When this maximum charge current limit is desired, leave
the CL pin open or set it to a voltage >1.05V such that
amplifier A5 can regulate the IBMON pin voltage accurately
to the internal reference of 1V.
When the output current waveform of the DC/DC converter
or the system load current is noisy, it is recommended that
a capacitor is connected to the CSP pin (C
reduce the AC content of the current through the sense
resistor (R
pick the value of C
than or equal to 50% of the average voltage across the
sense resistor. Similar to the IIMON pin, the voltage on the
IBMON pin is filtered further by putting a capacitor on the
pin (C
large as it will slow down the overall compensated charge
18
I
R
R
V
CLIM(MAX)
IBMON
CS
CL
IBMON
=
=
CL
I
20 • I
CLIM
= 20 • I
CS
is the voltage on the CL pin. The CL pin is
). This filter capacitor should not be arbitrarily
2.5µA
V
). Where the highest accuracy is important,
(A) =
CL
CLIM
• R
RCS
CS
R
0.050V
CSP
CS
⇒ I
• R
(Ω)
such that the AC content is less
CS
CLIM
= 20 • V
=
R
R
CL
CS
(
CSP
• 2.5µA
– V
CSP
CSN
). This is to
)
current regulation loop. For details on the loop compensa-
tion, refer to the Compensation section.
Battery Float Voltage Programming
When the value of R
float voltage is determined using the following formula:
When higher accuracy is important, a slightly more ac-
curate final float voltage can be determined using the
following formula:
where V
voltage regulation, which accounts for all the current
from all resistor dividers that are connected to this pin
(R
Low Battery Trickle Charge Programming and Bad
Battery Detection
When charging into an over-discharged or dead battery
(V
to 10% of the normal pull-up current. Therefore, the trickle
charge current is set using the following formula:
Therefore, when 50µA•R
relation is true:
Once the battery voltage rises above the low battery voltage
threshold, the charge current level rises from the trickle
charge current level to the full charge current level.
The LTC4000 also features bad battery detection. This
detection is disabled if the TMR pin is grounded or tied
to BIAS. However, when a capacitor is connected to the
R
CL
BFB
V
FBG
R
I
CLIM(TRKL)
FLOAT
BFB1
=
< V
= 100Ω typical).
I
CLIM(TRKL)
FBG
LOBAT
=
=
⎛
⎜
⎝
⎛
⎜
⎝
0.25µA
1.136V
V
is the voltage at the FBG pin during float
R
FLOAT
), the pull-up current at the CL pin is reduced
BFB1
=
I
R
CLIM
10
BFB2
• R
BFB1
+ R
– 1
CS
BFB2
is much larger than 100Ω, the final
⎞
⎟ R
⎠
⇒ I
CL
BFB2
is less than 1V, the following
• 1.136V
CLIM(TRKL)
⎞
⎟ –
⎠
= 0.25µA •
⎛
⎜
⎝
R
R
BFB2
BFB1
• V
R
R
FBG
CS
CL
4000f
⎞
⎟
⎠