LTC4000-1
32
40001fa
For more information www.linear.com/LTC4001-1
applicaTions inForMaTion
This same procedure is then repeated for the other four
loops: the input voltage regulation, the output voltage
regulation, the battery float voltage regulation and finally
the charge current regulation when V
OFB
> V
OUT(INST_ON)
.
Note that the resulting optimum values for each of the loops
may differ slightly. The final values of C
C
and R
C
are then
selected by combining the results and ensuring the most
conservative response for all the loops. This usually entails
picking the largest value of C
C
and the smallest value of
R
C
based on the results obtained for all the loops. In this
particular example, the value of C
C
is finally set to 47nF
and R
C
= 14.7kΩ.
BOARD LAYOUT CONSIDERATIONS
In the majority of applications, the most important param-
eter of the system is the battery float voltage. Therefore,
the user needs to be extra careful when placing and rout-
ing the feedback resistor R
BFB1
and R
BFB2
. In particular,
the battery sense line connected to R
BFB1
and the ground
return line for the LTC4000-1 must be Kelvined back
to where the battery output and the battery ground are
located respectively. Figure 27 shows this
Kelvin sense
configuration.
For accurate current sensing, the sense lines from R
IS
and R
CS
(Figure 27) must be Kelvined back all the way
to the sense resistors terminals. The two sense lines of
each resistor must also be routed close together and away
from noise sources to minimize error. Furthermore, cur-
rent filtering capacitors should be placed strategically to
ensure that very little AC current is flowing through these
sense resistors as mentioned in the applications section.
The decoupling capacitors C
IN
and C
BIAS
must be placed as
close to the LTC4000-1 as possible. This allows as short
a route as possible from C
IN
to the IN and GND pins, as
well as from C
BIAS
to the BIAS and GND pins.
In a typical application, the LTC4000-1 is paired with an
external DC/DC converter. The operation of this converter
often involves high dV/dt switching voltage as well as
high currents. Isolate these switching voltages and cur-
rents from the LTC4000-1 section of the board as much
as possible by using good board layout practices. These
include separating noisy power and signal grounds, having
a good low impedance ground plane, shielding whenever
necessary, and routing sensitive signals
as short as pos-
sible and away from noisy sections of the board.
Figure 27. Kelvin Sense Lines Configuration for LTC4000-1
40001 F27
V
IN
CSN
CLN
IN
CSP
BAT
GND
LTC4000-1
R
C
ITHGND
SWITCHING
CONVERTER
BGATE
ITH
IIDCC
C
C
IGATE
R
BFB1
R
IS
R
CS
R
BFB2
BFB
FBG
SYSTEM LOAD
