AAT4250_06 ANALOGICTECH [Advanced Analogic Technologies], AAT4250_06 Datasheet - Page 10

• Manufacturer Part Number: AAT4250_06
• Description: Slew Rate Controlled Load Switch
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

High Peak Output Current Applications
Some applications require the load switch to oper-
ate at a continuous nominal current level with short
duration, high-current peaks.
specification in the Absolute Maximum Ratings
table to ensure the AAT4250’s maximum pulsed
current rating is not exceeded. The duty cycle for
both output current levels must be taken into
account. To do so, first calculate the power dissi-
pation at the nominal continuous current level, and
then add the additional power dissipation due to
the short duration, high-current peak scaled by the
duty factor.
For example, a 4V system using an AAT4250 oper-
ates at a continuous 100mA load current level and
has short 2A current peaks, as in a GSM applica-
tion. The current peak occurs for 576µs out of a
4.61ms period.
First, the current duty cycle is calculated:
% Peak Duty Cycle: X/100 = 576µs/4.61ms
% Peak Duty Cycle = 12.5%
The load current is 100mA for 87.5% of the 4.61ms
period and 2A for 12.5% of the period. Since the
Electrical Characteristics do not report R
4V operation, it must be approximated by consulting
the chart of R
R
derive the R
= 183mΩ. Derated for temperature: 183mΩ x (1 +
0.002800 x (125°C -25°C)) = 235mΩ. The power
dissipation for a 100mA load is calculated as follows:
P
P
P
P
P
P
10
D(MAX)
D(100mA)
D(100mA)
D(87.5%D/C)
D(87.5%D/C)
D(87.5%D/C)
DS
can be scaled by the ratio seen in the chart to
= I
= (100mA)
= 2.35mW
2
OUT
= %DC x P
= 0.875 x 2.35mW
= 2.1mW
DS
DS(ON)
for 4V V
x R
DS
vs. V
2
x 235mΩ
D(100mA)
IN
IN
: 175mΩ x 120mΩ/115mΩ
. The R
Refer to the I
DS
reported for 5V
DS(MAX)
for
DM
Slew Rate Controlled Load Switch
The power dissipation for 100mA load at 87.5%
duty cycle is 2.1mW. Now the power dissipation for
the remaining 12.5% of the duty cycle at 2A is cal-
culated:
P
P
P
P
P
P
The power dissipation for 2A load at 12.5% duty
cycle is 117mW. Finally, the two power figures are
summed to determine the total true power dissipa-
tion under the varied load.
P
P
P
The maximum power dissipation for the AAT4250
operating at an ambient temperature of 85°C is
267mW. The device in this example will have a total
power dissipation of 120mW. This is well within the
thermal limits for safe operation of the device; in fact,
at 85°C, the AAT4250 will handle a 2A pulse for up
to 28% duty cycle. At lower ambient temperatures,
the duty cycle can be further increased.
Printed Circuit Board Layout
Recommendations
For proper thermal management, and to take
advantage of the low R
circuit board layout rules should be followed: V
and V
traces, and GND should be connected to a ground
plane. For best performance, C
be placed close to the package pins.
D(MAX)
D(2A)
D(2A)
D(12.5%D/C)
D(12.5%D/C)
D(12.5%D/C)
D(total)
D(total)
D(total)
OUT
= (2A)
= 940mW
= P
= 2.1mW + 117.5mW
= 120mW
= I
should be routed using wider than normal
2
D(100mA)
OUT
= %DC x P
= 0.125 x 940mW
= 117.5mW
2
x 235mΩ
x R
DS
+ P
D(2A)
DS(ON)
D(2A)
of the AAT4250, a few
IN
AAT4250
and C
4250.2006.03.1.3
OUT
should
IN