PRODUCT DATASHEET
AAT2789
SystemPowerTM
Low Noise, High Frequency Dual Step-Down Converter
Channel 1 Output Capacitor
VDROOP= 0.12V
3 · ΔILOAD
VDROOP · FS
3 · 1.5A
COUT3
=
=
= 20.8µF; use 22µF
0.12V · 1.8MHz
VOUT · (VIN(MAX) - VOUT
)
1
1.2V · (4.2V - 1.2V)
1
·
= 92mA
IRMS(MAX)
=
·
=
1.5µH · 1.8MHz · 4.2V
L · FS · VIN(MAX)
2· 3
2· 3
PESR = ESR · IRMS2 = 5mΩ · 24mA2 = 3µW
Channel 2 Output Capacitor
VDROOP= 0.1V
3 · ΔILOAD
VDROOP · FS
3 · 0.5A
COUT3
=
=
= 7.5µF; use 10µF
0.1V · 2MHz
VOUT · (VIN(MAX) - VOUT
)
1
3.3V · (4.2V - 3.3V)
3.3µH · 2MHz · 4.2V
1
·
= 30mA
IRMS(MAX)
=
·
=
L · FS · VIN(MAX)
2· 3
2· 3
PESR = ESR · IRMS2 = 5mΩ · 30mA2 = 4.5µW
Input Capacitor
Input Ripple VPP1 = 50mV, VPP2 = 25mV
1
1
CIN1
=
=
= 4.9µF
⎛ VPP1
⎝ IO1
⎞
⎛ 50mV
⎝ 1.5A
⎞
⎠
- ESR · 4 · FS
- 5mΩ · 4 · 1.8MHz
⎠
1
1
CIN2
=
=
= 3µF
⎛ VPP2
⎝ IO2
⎞
⎛ 25mV
⎝ 0.5A
⎞
- ESR · 4 · FS
- 5mΩ · 4 · 2MHz
⎠
⎠
CIN = CIN1+ CIN2 = 4.9μF+3μF= 7.9μF; use 10μF
IO1 + IO2
IRMS(MAX)
=
= 1A
2
P = ESR · IRMS2 = ESR · (1A)2 = 5mW
w w w . a n a l o g i c t e c h . c o m
2789.2008.03.1.0
19
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
