EUP8202-4.2/8.4
Board Layout Suggestions
∆I
)
)
When laying out the printed circuit board, the following
considerations should be taken to ensure proper operation
of the EUP8202.
L
(
max
2
V
=
=
OUT(RIPPLE)
GATE pin rise and fall times are 20ns and 50ns
respectively (with CGATE = 2000pF). To minimize
radiation, the catch diode, pass transistor and the input
bypass capacitor traces should be kept as short as
possible. The positive side of the input capacitor should
be close to the source of the P-channel MOSFET; it
provides the AC current to the pass transistor. The
connection between the catch diode and the pass
transistor should also be kept as short as possible. The
SENSE and BAT pins should be connected directly to the
sense resistor (Kelvin sensing) for best charge current
accuracy. Avoid routing the NTC PC board trace near the
MOSFET switch to minimize coupling switching noise
into the NTC pin.
(0.94A)(0.1Ω)
= 47mV
2
For dual cells charge,
VIN = 5V to 20V, VBAT = 8V nominal, IBAT =3A,
fOSC = 500kHz, IEOC=0.45A,
100mV
R
=
= 33mꢀ
SENSE
3A
Choose the inductor for about 50% ripple current at the
maximum VIN:
8V
500kHz)(0.5)(3A
8V
20V
L =
1 −
= 6.4µH
(
)
The compensation capacitor connected at the COMP pin
should return to the ground pin of the IC or as close to it
as possible. This will prevent ground noise from
disrupting the loop stability. The ground pin also works
as a heat sink, therefore use a generous amount of copper
around the ground pin. This is especially important for
high VCC and/or high gate capacitance applications.
Selecting a standard value of 6.8µH results in a
maximum ripple current of :
8V
8V
20V
∆I
=
1 −
= 1.441A
L
(
500kHz)(6.8µH
)
∆I
1.441A
2
L
ILPK = I
+
= 3A +
≈ 3.720A
CHG
2
The maximum power dissipation with VIN = 9V and VBAT
= 8V at 50℃ ambient temperature is:
2
(
3A) (55mΩ)(8V
)
P
=
= 0.44W
D
9V
TJ = 50℃ + (0.44W)(65℃/W) = 78.6℃
∆I
)
L
(
max
2
V
=
=
OUT(RIPPLE)
( )
= 72mV
2
The Schottky diode D2 shown in Figure 2 conducts
current when the pass transistor is off. In a low duty
cycle case, the current rating should be the same or
higher than the charge current. Also it should withstand
reverse voltage as high as VIN.
DS8202 Ver 1.1 Nov.2007
19
EUTECH [ EUTECH MICROELECTRONICS INC ]
