AAT1126 AAT, AAT1126 Datasheet - Page 13

• Manufacturer Part Number: AAT1126
• Description: Step-Down Converter
• Manufacturer: AAT

Thermal Calculations
There are three types of losses associated with the
AAT1126 step-down converter: switching losses,
conduction losses, and quiescent current losses.
1126.2006.05.1.1
Table 2: Adjustable Resistor Values For Use
V
OUT
1.85
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
2.0
2.5
3.3
(V)
With 0.6V Step-Down Converter.
GND
V
OUT
10µF
R2 = 59kΩ Ω
C1
R1 (kΩ Ω )
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
Figure 5: AAT1126 Adjustable Evaluation Board Schematic.
JP1
Enable
LX
R1
118K
R2
59K
1
2
3
R2 = 221kΩ Ω
R1 (kΩ Ω )
4.7µH
1000
L1
150
187
221
261
301
332
442
464
523
715
113
75
1
2
3
AAT1126
GND
EN
LX
600mA, 1MHz Step-Down Converter
Conduction losses are associated with the R
characteristics of the power output switching
devices. Switching losses are dominated by the
gate charge of the power output switching devices.
At full load, assuming continuous conduction mode
(CCM), a simplified form of the losses is given by:
I
The term t
down converter switching losses.
For the condition where the step-down converter is
in dropout at 100% duty cycle, the total device dis-
sipation reduces to:
Q
P
OUT
VIN
TOTAL
is the step-down converter quiescent current.
5
4
+ (t
=
I
P
O
sw
sw
2
TOTAL
· (R
· F · I
is used to estimate the full load step-
DSON(HS)
= I
O
O
+ I
2
C2
4.7µF
· R
Q
) · V
· V
V
DSON(HS)
C2 4.7µF 10V 0805 X5R
C1 10µF 6.3V 0805 X5R
U1 AAT1126 SOT23-5
L1 CDRH3D16-4R7
IN
O
IN
+ R
V
IN
DSON(LS)
+ I
AAT1126
Q
· V
· [V
IN
IN
- V
DS(ON)
O
])
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