AAT1120IES-0.6-T1 Advanced Analog Technology, Inc., AAT1120IES-0.6-T1 Datasheet - Page 13

• Manufacturer Part Number: AAT1120IES-0.6-T1
• Description: 500mA Step-Down Converter
• Manufacturer: Advanced Analog Technology, Inc.

Thermal Calculations
There are three types of losses associated with
the AAT1120 step-down converter: switching loss-
es, conduction losses, and quiescent current loss-
es. Conduction losses are associated with the
R
ing devices. Switching losses are dominated by
the gate charge of the power output switching
devices. At full load, assuming continuous conduc-
tion mode (CCM), a simplified form of the losses is
given by:
I
The term t
down converter switching losses.
1120.2007.01.1.0
Q
GND
DS(ON)
P
VIN
TOTAL
is the step-down converter quiescent current.
characteristics of the power output switch-
=
+ (t
I
sw
O
sw
2
· (R
is used to estimate the full load step-
· F
C1
4.7μF
S
DS(ON)H
· I
O
+ I
· V
Q
) · V
O
+ R
IN
V
DS(ON)L
IN
1
2
3
4
VP
VIN
GND
FB
· [V
Figure 1: AAT1120 Schematic.
AAT1120
IN
- V
U1
O
])
PGND
N/C
EN
LX
8
7
6
5
LX
For the condition where the step-down converter is
in dropout at 100% duty cycle, the total device dis-
sipation reduces to:
Since R
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range.
Given the total losses, the maximum junction tem-
perature can be derived from the θ
STDFN22-8 package which is 50°C/W.
500mA Step-Down Converter
L1
DS(ON)
P
TOTAL
T
J(MAX)
, quiescent current, and switching
C2
4.7μF
= I
= P
O
2
· R
TOTAL
DS(ON)H
R2
59kΩ
R1
Adj.
· Θ
JA
+ I
+ T
AAT1120
Q
· V
AMB
C3
(optional)
100pF
IN
JA
+VOUT
GND
for the
13