Datasheet

LTC3816
39
3816f
Figure 22. Sense Resistor and Inductor DCR
Kelvin Current Sensing
applicaTions inForMaTion
As can be seen from the above equation, the biggest portion
of the output ripple comes from the ESR of the capacitor.
This is why low ESR capacitors are so important in low
voltage, high current applications.
PC B
OARD LAYOUT CHECKLIST
When laying out the printed circuit board, start with the
power devices. Be sure to orient the power circuitry so
that a clean flow of the power path is achieved. Conductor
widths should be maximized and lengths minimized. After
you are satisfied with the power path, the control circuitry
should be laid out. It is much easier to find routes for the
relatively small traces in the control circuits than it is to
find circuitous routes for high current paths. After the
layout, the following checklist should be used to ensure
proper operation of the LTC3816.
1.
K
eep the GND and BSOURCE traces separate. The signal
ground consists of the LTC3816 GND pin and the (–)
terminal of V
OUT
. The power ground consists of the
BSOURCE pin, the Schottky diode anode, the source
of the bottom side MOSFET, and the (–) terminal of the
input capacitor. Also, try to connect the (–) terminal
of the output capacitor as close as possible to the (–)
terminals of the input capacitor. Place the LDO ceramic
capacitor C
INTVCC
next to the IC, between INTV
CC
and
GND. The negative terminals of C
IN
, C
OUT
and C
INTVCC
should be as close as possible to one another.
2. The
high di/dt loop formed by the top MOSFET, the
bottom MOSFET and the C
IN
capacitor should have
short leads and PC trace lengths to minimize high
frequency noise and voltage stress from inductive
ringing.
3.
Connect the drain of the topside MOSFET directly to the
(+) plate of C
IN
, and connect the source of the bottom
side MOSFET directly to the (–) terminal of C
IN
. This
capacitor provides the AC current to the MOSFETs.
4. The
charge pump capacitor, C
B
, should also be next
to the IC between BOOST and SW.
5. Place
the small-signal components away from high
frequency switching nodes (BOOST, SW, TG and
BG).
6. The AITC amplifier external components should be
placed close to the LTC3816. Only the NTC or PTC
thermistor should be placed near the inductor.
7.
Are the V
CC(SEN)
and V
SS(SEN)
, I
SENP
and I
SENN
leads
routed together with minimum PC trace spacing? The
filter capacitor between V
CC(SEN)
and V
SS(SEN)
and the
filter capacitor between I
SENP
and I
SENN
should be as
close as possible to the LTC3816. Ensure accurate
current sensing with Kelvin connections as shown in
Figure 22.
8.
To prevent I
MON
current from affecting the output
voltage kelvin sense accuracy, the I
MON
resistor and
V
SS(SEN)
should be connected to the CPU V
SS(SEN)
pin
using separate PCB traces.
9. Since
the IC ground will normally return to the ground
planes on the PCB through an array of vias, be sure
to avoid having any high di/dt power path currents
flowing under the IC.
10. Any
external small-signal components that are con-
nected to ground should be located as close as pos-
sible to the IC, with local connections to GND or the
ground plane using vias.
I
SENP
LTC3816
INDUCTOR
OUTPUT CAPACITOR
SENSE
RESISTOR
I
SENN
C
ISR
R
ISR
C
ISR
R
ISR
INDUCTOR
3816 F22
OUTPUT CAPACITOR
SW
I
SENP
LTC3816
I
SENN