AAT1156
1MHz 700mA Step-Down DC-DC Converter
Output Capacitor Ripple Current:
VOUT · (VIN - VOUT
)
1
2.5V · (4.2V - 2.5V)
= 62mArms
4.7µH · 1MHz · 4.2V
1
·
IRMS
=
·
=
L·F·V
2· 3
2· 3
IN
Pesr = esr · IRMS2 = 5mΩ · (62 mA)2 = 19µW
AAT1156 Dissipation:
IO2 · (RDSON(HS) · VO + RDSON(LS) · (VIN -VO))
PTOTAL
=
+ (tsw · F · IO + IQ) · VIN
VIN
(0.7A)2 · (0.17Ω · 2.5V + 0.16Ω · (4.2V - 1.5V))
=
+ (20nsec · 1MHz · 0.7A + 300µA) · 4.2V = 0.141W
4.2V
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + 50°C/W · 0.141W = 92°C
U1
AAT1156
AAT1156 Efficiency
(VOUT = 0.8V; L = 2.2µH; CDRH3D16)
INPUT
0.8V
12
11
10
7
4
VP
FB
LX
R3
15
14
13
16
3
100
90
80
70
60
50
40
30
20
R1
100
19.6k
VP
L1
2.2µH
VP
LX
C1
10µF
VIN = 2.7V
EN
LX
9
VCC
LL
N/C
VIN = 4.2V
R4
59k
C3, C4
6
PGND
PGND
PGND
2 x 22µF
VIN = 3.6V
C2
0.1 µF
8
2
N/C
SGND
5
1
C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
C3, C4 MuRata 22µF 6.3V GRM21BR60J226ME39L X5R 0805
L1 Sumida CDRH3D16-2R2NC
1
10
100
1000
Output Current (mA)
Figure 5: 0.8V Solution.
12
1156.2005.11.1.2
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
