AAT3680 Advanced Analogic Technologies, AAT3680 Datasheet - Page 11

• Manufacturer Part Number: AAT3680
• Description: Lithium-Ion Linear Battery Charge Controller
• Manufacturer: Advanced Analogic Technologies

2. The next step is to determine which size package
is needed to keep the junction temperature below its
rated value, T
mum ambient temperature inside the system T
calculate the thermal resistance R
It is recommended to choose a package with a lower
R
package would be an acceptable choice, as it has an
R
quately sized copper pad soldered to the heat tab.
3. Choose a drain-source (V
greater than the input voltage. In this example, V
is 5.0V, so a 12V device is acceptable.
4. Choose a MOSFET with a drain current rating at
least
I
select a device with at least 1.125A rating.
3680.2003.4.0.91
CHARGE(REG)
JA
JA
P
P
P
D
D
D
of 62.5°C/W when mounted to a PCB with ade-
than the number calculated above. A SOT223
= (V
= (5.5V - 0.1V - 0.4V - 3.1V) · 750mA
= 1.4W
50%
P(MAX)
R
R
R
value.
J(MAX)
VP
Figure 5: Typical Applications Schematic Using P-Channel Power MOSFET
greater
JA
JA
JA
- V
=
=
= 79°C/W
. Using this value, and the maxi-
(T
(150 - 40)
CS
J(MAX)
In this example we would
- V
1.4
than
D
P
- V
- T
D
MIN
A(MAX)
C1
4.7 F
R
100k
the
0.2
DS
SENSE
R4
) · I
JA
) voltage rating
)
required:
CHARGE(REG)
programmed
RFD10P03L
Lithium-Ion Linear Battery Charge Controller
Q1
R1
1k
A(MAX)
P
,
DRV
CSI
VP
VSS
AAT3680
5. Calculate the required threshold voltage to deliv-
er I
where V
vided by the AAT3680, V
sense resistor, V
DRV pin, and V
(assuming 10% tolerance on the 5V supply). Choose
a MOSFET device with sufficiently low V
device will conduct the desired I
6. Calculate the worst case maximum allowable
R
Select a P-Channel Power MOSFET with R
lower than 197m
In summary, select a P-Channel MOSFET with ratings
V
V
STAT
BAT
T2X
DS
GS
DS(ON)
TS
CHARGE(REG)
= -4.3V in a SOT223 (or better thermal) package.
D1
R2
1k
V
V
V
12V, R
GS
GS
GS
GS
at worst case V
R
R
R
DS(ON)
DS(ON)
DS(ON)
= (V
= (0.1V + 0.1V) - 4.5V
= -4.3V
is the available gate to source voltage pro-
JA
CS
:
P(MIN)
OL@DRV
VP
=
=
= 197m
+ V
RT1
(V
RT2
(4.5V - 0.11V - 4.242V)
79°C/W and R
at V
P(MIN)
C2
10 F
OL@DRV
is the worst case input voltage
is the rated low voltage at the
GS
GS
BATT+
BATT-
CS
TEMP
I
CHARGE(REG)
- V
= -4.3V.
voltage:
0.75A
is the voltage across the
) - V
Battery
CS(MAX)
Pack
CHARGE(REG)
P(MIN)
DS(ON)
AAT3680
- V
GS(TH)
BAT(MAX)
197m
.
so the
DS(ON)
)
11
at