AAT1162
12V, 1.5A Step-Down DC/DC Converter
The external resistors set the output voltage
according to the following equation:
Inductor Selection
For most designs, the AAT1162 operates with
inductors of 2µH to 4.7µH. For output voltages
above 3.3V, the minimum recommended inductor is
3.8µH. For 3.3V and below, use a 2 to 2.2µH induc-
tor. For optimum voltage-positioning load transients,
choose an inductor with DC series resistance in the
15mꢁ to 20mꢁ range. For higher efficiency at
heavy loads (above 1A), or minimal load regulation
(but some transient overshoot), the resistance
should be kept below 18mꢁ. The DC current rating
of the inductor should be at least equal to the max-
imum load current plus half the ripple current to pre-
vent core saturation (1.5A + 263mA). Table 2 lists
some typical surface mount inductors that meet tar-
get applications for the AAT1162.
⎛
R1⎞
R2⎠
V
OUT = 0.6V 1 +
⎝
or
V
⎛
⎝
⎞
-1 · R2
⎠
OUT
R1 =
V
REF
Table 1 shows the resistor selection for different
output voltage settings.
R2 = 5.9(kΩ)
R1 (kΩ)
R2 = 59(kΩ)
R1 (kΩ)
Manufacturer's specifications list both the inductor
DC current rating, which is a thermal limitation, and
the peak current rating, which is determined by the
saturation characteristics. The inductor should not
show any appreciable saturation under normal load
conditions. Some inductors may meet the peak and
average current ratings yet result in excessive loss-
es due to a high DCR. Always consider the losses
associated with the DCR and its effect on the total
converter efficiency when selecting an inductor.
For example, the 3.7ꢀH CDR7D43 series inductor
selected from Sumida has an 18.9mΩ DCR and a
4.3ADC current rating. At full load, the inductor DC
loss is 28mW which gives only a 0.4% loss in effi-
ciency for a 1.5A, 5V output.
VOUT (V)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
5.0
1.96
2.94
3.92
4.99
5.90
6.81
7.87
8.87
11.8
12.4
13.7
18.7
26.7
43.2
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
432
Compensation
The AAT1162 step-down converter uses peak cur-
rent mode control with slope compensation
scheme to maintain stability with lower value induc-
tors for duty cycles greater than 50%. The regula-
tion feedback loop in the IC is stabilized by the
components connected to the COMP pin, as
shown in Figure 1.
Table 1: Resistor Selection for Different Output
Voltage Settings. Standard 1% Resistors are
Substituted for Calculated Values.
12
1162.2007.09.1.2
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