AAT1146IJS-0.6-T1 Analogic Tech, AAT1146IJS-0.6-T1 Datasheet - Page 11

• Manufacturer Part Number: AAT1146IJS-0.6-T1
• Description: Switching Converters, Regulators & Controllers Fast Transient 400mA DC/DC Converter
• Manufacturer: Analogic Tech

Specifications of AAT1146IJS-0.6-T1

• Output Voltage: 0.6 V (Adj.)
• Output Current: 400 mA (Max)
• Input Voltage: 2.7 V
• Switching Frequency: 1 MHz
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SC70JW-8
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

SwitchReg
Applications Information
Inductor Selection
The step-down converter uses peak current mode con-
trol with slope compensation to maintain stability for
duty cycles greater than 50%. The output inductor value
must be selected so the inductor current down slope
meets the internal slope compensation requirements.
The internal slope compensation for the adjustable and
low-voltage fixed versions of the AAT1146 is 0.24A/μsec.
This equates to a slope compensation that is 75% of the
inductor current down slope for a 1.5V output and 4.7μH
inductor.
This is the internal slope compensation for the adjust-
able (0.6V) version or low-voltage fixed versions. When
externally programming the 0.6V version to 2.5V, the
calculated inductance is 7.5μH.
In this case, a standard 6.8μH value is selected.
For high-voltage fixed versions (≥2.5V), m = 0.48A/
μsec. Table 1 displays inductor values for the AAT1146
fixed and adjustable options.
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 satura-
tion 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 losses 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.
The 4.7μH CDRH3D16 series inductor selected from
Sumida has a 105mΩ DCR and a 900mA DC current rat-
ing. At full load, the inductor DC loss is 17mW which gives
a 2.8% loss in efficiency for a 400mA, 1.5V output.
1146.2009.05.1.7
L =
m =
= 3
0.75 ⋅ V
0.75 ⋅ V
μsec
TM
A
m
L
⋅ 2.5V = 7.5μH
O
O
=
=
0.24A
0.75 ⋅ 1.5V
0.75 ⋅ V
4.7μH
μsec
A
O
≈
= 0.24
3
μsec
A
μsec
A
⋅ V
w w w . a n a l o g i c t e c h . c o m
O
Fast Transient 400mA Step-Down Converter
Input Capacitor
Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for
the input. To estimate the required input capacitor size,
determine the acceptable input ripple level (V
solve for C. The calculated value varies with input volt-
age and is a maximum when V
voltage.
Always examine the ceramic capacitor DC voltage coef-
ficient characteristics when selecting the proper value.
For example, the capacitance of a 10μF, 6.3V, X5R
ceramic capacitor with 5.0V DC applied is actually about
6μF.
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.
0.6V Adjustable With
External Feedback
Confi guration
Fixed Output
V
V
IN
I
O
V
V
RMS
IN
O
Table 1: Inductor Values.
· 1 -
C
⎛
⎝
· 1 -
IN(MIN)
= I
C
⎛
⎝
O
IN
V
V
·
=
=
IN
O
PRODUCT DATASHEET
V
V
Output Voltage
⎞
⎠
⎛
⎝
⎛
⎝
IN
O
V
V
V
V
V
V
=
⎞
⎠
0.6V to 3.3V
IN
I
O
I
IN
O
O
O
PP
PP
1.5V, 1.8V
2.5V, 3.3V
1V, 1.2V
=
· 1 -
· 1 -
D · (1 - D) =
- ESR · F
1
4
- ESR · 4 · F
⎛
⎝
⎛
⎝
for V
AAT1146
1
IN
V
V
V
V
⎞
⎠
⎞
⎠
IN
is double the output
O
IN
IN
O
⎞
⎠
⎞
⎠
= 2 × V
S
S
0.5
Inductor
O
2.2μH
4.7μH
6.8μH
4.7μH
2
=
PP
1
2
) and
11