AAT2146W Datasheet, PDF (13/18 Pages) Skyworks Solutions Inc. – Low-Noise, Fast Transient 600mA Step-Down Converter

DATA SHEET
AAT2146W
Low-Noise, Fast Transient 600mA Step-Down Converter
V_OUT (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
R2 = 59k
R1 (k)
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
R2 = 221k
R1 (k)
75
113
150
187
221
261
301
332
442
464
523
715
1000
Table 2: Adjustable Resistor Values For Use With
0.6V Step-Down Converter.
Thermal Calculations
There are three types of losses associated with the
AAT2146W step-down converter: switching losses, con-
duction losses, and quiescent current losses. Conduction
losses are associated with the R_DS(ON) characteristics of
the power output switching devices. Switching losses are
dominated by the gate charge of the power output
switching devices. A simplified form of the losses is given
by:
P_TOTAL
=
I_O2
·
(R_DS(ON)HS
·
V_O
+ R_DS(ON)LS
V_IN
·
[V_IN
-
V_O])
+ (t_sw · f_sw · I_O + I_Q) · V_IN
I_Q is the step-down converter quiescent current. The
term t_sw is used to estimate the full load step-down con-
verter switching losses.
For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
P_TOTAL = I_O2 · R_DS(ON)HS + I_Q · V_IN
Since R_DS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be inves-
tigated over the complete input voltage range.
Given the total losses, the maximum junction tempera-
ture can be derived from the _JA for the SC70JW-8 pack-
age which is 160°C/W.
T_J(MAX) = P_TOTAL · Q_JA + T_A
1
2
3
Enable
V_IN
C4
100pF
V_OUT =1.8V
R1
L1 ^118k
4.7µH
C1
10µF
C3
n/a
R2
59k
GND
LX
U1
AAT2146W
1
8
EN PGND
2
7
OUT PGND
3
6
VIN PGND
4
5
LX AGND
C2
4.7µF
U1 AAT2146W SC70JW-8
L1 CDRH3D16-4R7
C2 4.7µF 10V 0805 X5R
C1 10µF 6.3V 0805 X5R
Figure 5: AAT2146W Adjustable Evaluation Board Schematic.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202008A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
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