AAT1154(2003) 데이터 시트보기 (PDF) - Analog Technology Inc
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AAT1154 Datasheet PDF : 16 Pages
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Sumida inductor Series CDRH6D38.
∆I = VO
L·F
1- VO =
VIN
3.3V
1.5µH ·1MHz
1-
3.3V
5.25V
= 0.82A
I PK
=
IOUT +
∆I
2
=
3A + 0.41A = 3.41A
AAT1154 Junction Temperature
PON = IO2
·
RDS(ON)
VIN
·
VO
+ tSW
·
F·
2
IO
+
IQ
·
VIN
=
32
·
65mΩ
5V
·
3.3V
+
20ns
·
1MHz
2
·
3A
+
750µA
·
5V
=
0.539 Watts
TJ(MAX)= TAMB + ΘJA · P =
70°C +110°C /W · 0.54W = 129°C
Diode
IDIODE= IO · 1-
VO
VIN
=
3A · 1 -
3.3V
5V
= 1.02A
VFW = 0.35V
PDIODE =VFW · IDIODE =
0.35V ·1.01A = .354W
AAT1154
1MHz 3A Buck DC/DC Converter
Given a case to ambient thermal resistance of
120°C/W from the manufacturer's data sheet,
TJ(MAX) of the diode is
TJ(MAX)= TAMB + ΘJA · P =
70°C +120°C /W · 0.354W=
112°C
Output Capacitor
The output capacitor value required for sufficient
loop phase margin depends on the type of capaci-
tor selected. For a low ESR ceramic capacitor a
minimum value of 200µF is required. For a low
ESR tantalum capacitor lower values are accept-
able. While the relatively higher ESR associated
with the tantalum capacitor will give more phase
margin and a more damped transient response, the
output voltage ripple will be higher.
The 120µF Vishay 594D tantalum capacitor has an
ESR of 85 mΩ and a ripple current rating of 1.48
Arms in a C case size. Although smaller case sizes
are sufficiently rated for this ripple current, their
ESR level would result in excessive output ripple.
The ESR requirement for a tantalum capacitor can
be estimated by
ESR ≤VRIPPLE=100mV= 121mΩ
∆I 0.82A
IRMS =
1
2·
3
· (VOUT+ VFWD)· (VIN
L · F · VIN
-
VOUT) =
1 · 3.65V·1.7V = 240mArms
2· 3 1.5µH· 1MHz·5V
Two or three 1812 X5R 100uF 6.3V ceramic
capacitors in parallel also provide sufficient phase
margin. The low ESR and ESL associated with
ceramic capacitors also reduces output ripple sig-
nificantly over that seen with tantalum capacitors.
Temperature rise due to ESR ripple current dissi-
pation is also reduced.
1154.2003.08.0.91
13
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