AAT1123IJS-1.2-T1 Advanced Analog Technology, Inc., AAT1123IJS-1.2-T1 Datasheet - Page 11

• Manufacturer Part Number: AAT1123IJS-1.2-T1
• Description: 1MHz Step-Down Converter
• Manufacturer: Advanced Analog Technology, Inc.

The maximum input capacitor RMS current is:
The input capacitor RMS ripple current varies with
the input and output voltage and will always be less
than or equal to half of the total DC load current.
for V
1123.2007.02.1.6
I
RMS(MAX)
V
V
IN
IN
Figure 2: AAT1123 Evaluation Board
O
= 2 x V
=
I
RMS
· 1 -
⎛
⎝
I
2
O
= I
V
O
V
O
IN
O
·
⎞
⎠
=
V
V
Top Side.
IN
O
D · (1 - D) =
· 1 -
⎛
⎝
V
V
IN
O
⎞
⎠
Figure 4: AAT1123 Evaluation Board
0.5
2
=
1
2
Bottom Side.
The term
age ripple and input capacitor RMS current equations
and is a maximum when V
the input voltage ripple and the input capacitor RMS
current ripple are a maximum at 50% duty cycle.
The input capacitor provides a low impedance loop
for the edges of pulsed current drawn by the
AAT1123. Low ESR/ESL X7R and X5R ceramic
capacitors are ideal for this function. To minimize
stray inductance, the capacitor should be placed
as closely as possible to the IC. This keeps the
high frequency content of the input current local-
ized, minimizing EMI and input voltage ripple.
The proper placement of the input capacitor (C2) can
be seen in the evaluation board layout in Figure 2.
Figure 3: Exploded View of Evaluation
1MHz Step-Down Converter
V
V
O
IN
· 1 -
Board Top Side Layout.
⎛
⎝
V
V
IN
O
⎞
⎠
appears in both the input volt-
O
is twice V
AAT1123
IN
. This is why
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