AAT1123 Datasheet, PDF (13/20 Pages) Advanced Analogic Technologies – 1MHz 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 = 59kΩ
R1 (kΩ)
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
R2 = 221kΩ
R1 (kΩ)
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
AAT1123 step-down converter: switching losses,
conduction losses, and quiescent current losses.
AAT1123
1MHz Step-Down Converter
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.
At full load, assuming continuous conduction mode
(CCM), a simplified form of the losses is given by:
P_TOTAL
=
I_O2
·
(R_DSON(HS)
·
V_O
+ R_DSON(LS)
V_IN
·
[V_IN
-
V_O])
+ (t_sw · F · 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 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:
P_TOTAL = I_O2 · R_DSON(HS) + I_Q · V_IN
1
2
3
V_IN
Enable
V_OUT
C1
22μF
GND
R1 118k
L1
4.7μH
R2
59k
U1
AAT1123
1 _{EN PGND} 8
2 _{OUT PGND} 7
3 _{VIN PGND} 6
4 _{LX AGND} 5
C2
4.7μF
GND2
LX
U1 AAT1123 SC70JW-8
L1 CDRH3D16-4R7
C1 22μF 6.3V 0805 X5R
C2 4.7μF 6.3V 0805 X5R
Figure 5: AAT1123 Adjustable Evaluation Board Schematic.
1123.2006.05.1.5
13