LTC4040_15 Datasheet, PDF (23/26 Pages) Linear Technology – 2.5A Battery Backup Power Manager

LTC4040
natural least-area path, excessive voltage will build
up and radiated emissions will occur. So every effort
should be made to keep the hot-loop current path as
unbroken as possible.
3586 F04
Figure 4. High Frequency Ground Currents Follow Their Incident Path.
Slices in the Ground Plane Cause High Voltage and Increased EMI
3. The other important components that need to be placed
close to the pins are the C_BAT capacitor and the inductor
L1. Even though the current through these components
is continuous, they can change very abruptly due to a
sudden change in load demand. Also, their traces should
be wide enough to handle currents as high as the NMOS
current limit (typ. 6.5A) in backup boost mode.
4. Locate the V_SYS dividers for BSTFB and RSTFB near the
part but away from the switching components. Kelvin
the top of the resistor dividers to the positive terminal of
C_SYS. The bottom of the resistor dividers should return
to the ground plane away from the hot-loop current
path. The same is true for the PFI divider.
5. The exposed pad on the backside of the LTC4040 pack-
age must be securely soldered to the PC board ground
and also must have a group of vias connecting it to the
ground plane for optimum thermal performance. Also
this is the only ground pin in the package, and it serves
as the return path for both the control circuitry and the
switching converter.
6. The IGATE pin for controlling the gates of the external
pass transistors has extremely limited drive current.
Care must be taken to minimize leakage to adjacent
PC board traces. To minimize leakage, the trace can be
guarded on the PC board by surrounding it with V_SYS
connected metal.
Typical Application
5V Backup System with 12V Buck for Automotive Application
(Charge Current Setting: 1A, Input Current Limit Setting: 2A)
V_IN
12V
4.7µF
V_IN
EN/UV
BST
10nF
PG LT8610
SYNC
TR/SS
SW
BIAS
1µF
FB
INTV_CC
RT PGND GND
0.1µF
4.7µH
1M
10pF
18.2k
243k
V_OUT
5V
47µF
178k
60.4k
R_S
12mΩ
MN2
V_IN CLN
OVSNS
PFI
IGATE
V_SYS
BSTFB
RSTFB
FAULT
PFO
RST
CHRG
CLPROG
LTC4040
CHGOFF BSTOFF GND F0 F1 F2
SW
BAT
NTC
PROG
2k
V_SYS
5V
1690k
324k
2.2µH
V_OUT
SYSTEM
LOAD
100µF
10µF
+
NTC
Li-Ion
4.1V
4040 TA02
L1: COILCRAFT XAL-5030-222
MN2: VISHAY/SILICONIX SIR424DP-T1-GE3
4040fa
For more information www.linear.com/LTC4040
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