AAT1110_06 Datasheet, PDF (14/19 Pages) Advanced Analogic Technologies – Fast Transient 800mA Step-Down Converter

AAT1110
Fast Transient 800mA Step-Down Converter
The adjustable version of the AAT1110, combined
with an external feedforward capacitor (C4 in
Figure 1), delivers enhanced transient response for
extreme pulsed load applications. The addition of
the feedforward capacitor typically requires a larg-
er output capacitor C1 for stability.
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
75K
113K
150K
187K
221K
261K
301K
332K
442K
464K
523K
715K
1.00M
Table 2: Adjustable Resistor Values For Use
With 0.6V Step-Down Converter.
Thermal Calculations
There are three types of losses associated with
the AAT1110 step-down converter: switching loss-
es, conduction losses, and quiescent current loss-
es. Conduction losses are associated with the
R_DS(ON) characteristics of the power output switch-
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 LDO
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.
V_IN
V_OUT
C1
10μF
GND
1
2
3
Enable
R1
118k
L1
4.7μH
R2
59k
U1
AAT1110
1 _{EN PGND} 8
2 _{OUT PGND} 7
3 _{VIN PGND} 6
4 _{LX AGND} 5
C2
4.7μF
GND2
LX
U1 AAT1110 SC70JW-8
L1 CDRH3D16-4R7
C1 10μF 10V 0805 X5R
C2 4.7μF 10V 0805 X5R
Figure 5: AAT1110 Adjustable Evaluation Board Schematic.
14
1110.2006.04.1.0