AAT1151IKS-1.0-T1 AnalogicTech, AAT1151IKS-1.0-T1 Datasheet - Page 10

• Manufacturer Part Number: AAT1151IKS-1.0-T1
• Description: DC to DC Converter, 850kHz 700mA Synchronous Buck DC/DC Converter, Tape and Reel
• Manufacturer: AnalogicTech

Thermal Calculations
There are two types of losses associated with the
AAT1151 output switching MOSFET, switching loss-
es and conduction losses. The conduction losses
are associated with the R
output switching device. At the full load condition,
assuming continuous conduction mode (CCM), a
simplified form of the total losses is given by
where I
10
+ (t
P =
SW
I
O
q
·
2 · (R
F I
is the AAT1151 quiescent current.
·
O
DSON(HS)
·
V
Figure 4: QFN Evaluation Board
IN
+ I
Figure 2: MSOP Evaluation
· V
Q
) · V
O
Board Top Layer
V
DS(ON)
+ R
IN
IN
Top Side
DSON(LS)
characteristics of the
· (V
IN
850kHz 700mA Synchronous Buck DC/DC Converter
· V
O
))
Once the total losses have been determined the
junction temperature can be derived from the θ
for the MSOP-8 package.
Adjustable Output
For applications requiring an output other than the
fixed available, the 1V version can be programmed
externally. Resistors R3 and R4 of figure 5 force
the output to regulate higher than 1 Volt. R4 should
be 100 times less than the 1MΩ internal resistance
of the FB pin (recommended 10kΩ). Once R4 is
selected R3 can be calculated. For a 1.25 Volt out-
put with R4 set to 10.0kΩ, R3 is 2.55kΩ.
R3 = (V
Figure 5: QFN Evaluation Board
Figure 3: MSOP Evaluation
Board Bottom Layer
O
- 1) · R4 = 0.25 · 10kΩ = 2.55kΩ
Bottom Side
T
J
= P · θ
JA
+ T
AMB
AAT1151
1151.2003.11.0.91
JA