PRODUCT DATASHEET
AAT1217
SwitchRegTM
600mA, 1.2MHz, Micropower Synchronous Step-Up Converter
X7R and X5R ceramic capacitors are ideal for this func-
VIN · (VOUT - VIN)
IOUT · VOUT
IPEAK
=
+
tion. To minimize stray inductance, the capacitor should
be placed as close as possible to the IC. This keeps the
high frequency content of the input current localized,
minimizing EMI and input voltage ripple. Always exam-
ine the ceramic capacitor DC voltage coefficient charac-
teristics to get the proper value. For example, the
capacitance of a 10ꢀF, 6.3V, X5R ceramic capacitor with
5.0V DC applied is actually about 6ꢀF.
η · VIN
2L · FSW · VOUT
IPEAK Peak Inductor Current
IDC DC Component (Average) of the Inductor Current
ΔIL Peak-Peak Inductor Ripple Current
IOUT Output (Load) Current
VOUT Output Voltage
VIN Input Voltage
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the eval-
uation board input voltage pins. The inductance of these
wires, along with the low-ESR ceramic input capacitor,
can create a high Q network that may affect converter
performance. This problem often becomes apparent in
the form of excessive ringing in the output voltage dur-
ing load transients which can produce errors in loop
phase and gain measurements. Since the inductance of
a short printed circuit board (PCB) trace feeding the
input voltage is significantly lower than the power leads
from the bench power supply, most actual applications
do not exhibit this problem. In applications where the
input power source lead inductance cannot be reduced
to a level that does not affect the converter perfor-
mance, a high ESR tantalum or aluminum electrolytic
capacitor should be placed in parallel with the low ESR,
ESL bypass input ceramic capacitor. The introduction of
the high ESR capacitor dampens the high Q network and
stabilizes the AAT1217.
η
AAT1217 Efficiency (consult the performance graphs
in the “Typical Characteristics” section of the data
sheet)
D
Steady-State Duty Cycle
FSW Switching Frequency
Inductor Value
L
For a given chosen inductor value and application condi-
tions make sure the peak inductor current does not
exceed the maximum current rating of the selected ven-
dor’s inductor. For optimum load transient and efficien-
cy, low DCR inductors should be selected. Table 2 lists
some typical surface mount inductors that are suitable
for typical AAT1217 applications.
Input Capacitor
A surface mount 4.7μF or greater, X5R or X7R, ceramic
capacitor is suggested for the input capacitor. The input
capacitor provides a low impedance loop for the edges
of pulsed current drawn by the AAT1217. Low ESR/ESL
Part Number
L (μH)
Max DCR (mΩ)
Rated DC Current (A)
Size WxLxH (mm)
2.2
4.7
10
2.2
4.7
10
2.2
4.7
10
2.2
4.7
10
2.2
4.7
10
4.7
10
123
238
431
1.15
0.75
0.53
1.12
0.8
Sumida CDH28D11/S
3x3.3x1.2
140 (typ)
246 (typ)
446 (typ)
100
Coiltronics SD3112
TDK VLF3012A
Sumida CR43
3.1x3.1x1.2
2.8x2.6x1.2
4.3x4.8x3.5
0.55
1
190
410
0.74
0.49
1.75
1.15
1.04
2.04
1.32
1
71.2
108.7
182
31.3
72
128
45
90
Sumida CDRH4D28
Toko D53LC
5.0x5.0x3.0
5.0x5.0x3.0
1.87
1.33
Table 2: Typical Surface Mount Inductors.
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1217.2008.03.1.3
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