LTC4000_15 Datasheet, PDF (29/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging and Power Management

LTC4000
Applications Information
This same procedure is then repeated for the other four
loops: the input current 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 routing
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 must be Kelvined back to where the
battery output and the battery ground are located respec-
tively. Figure 19 shows this Kelvin sense configuration.
For accurate current sensing, the sense lines from R_IS
and R_CS (Figure 19) 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 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 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 currents
from the LTC4000 section of the board as much as pos-
sible by using good board layout practices. These include
separating noisy power and signal grounds, having a good
low impedance ground plane, shielding whenever neces-
sary, and routing sensitive signals as short as possible
and away from noisy sections of the board.
SWITCHING
CONVERTER
GND ITH
R_C
ITH
CLN
R_IS
IN
C_C
CC IID _IGATE
CSP
LTC4000
CSN
BGATE
BAT
V_IN
BFB
GND
FBG
SYSTEM LOAD
R_CS
R_BFB1
R_BFB2
4000 F19
Figure 19. Kelvin Sense Lines Configuration for LTC4000
For more information www.linear.com/LTC4000
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