AAT2153 Datasheet, PDF (15/17 Pages) Advanced Analogic Technologies – 2.5A Low Noise Step-Down Converter

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PRODUCT DATASHEET
AAT2153
2.5A Low Noise Step-Down Converter
Design Example
Specifications
V_O 3.3V @ I_O = 2.5A, Pulsed Load ΔI_LOAD = 2.4A
V_IN 2.7V to 4.2V (3.6V nominal)
F_S 1.4MHz
T_AMB 85°C in QFN33-16 Package
Output Inductor
L = V_O (μH) = 3.3μH; see Table 2.
For Wurth inductor 7447789003 3.3μH DCR = 30mΩ max.
ΔI =
V_O
L · F_S
·
1-
V_O
V_IN
=
3.3V
3.3µH · 1.4MHz
·
1-
3.3V
4.2V
= 153mA
I_PK
=
I_O
+
ΔI
2
= 2.5A + 0.077A = 2.577A
P_L = I_O2 · DCR = 2.5A² · 30mΩ = 188mW
Output Capacitor
V_DROOP = 0.2V
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 2.4A
0.2V · 1.4MHz
= 25.7µF; use 2x22µF
I = _RMS(MAX)
1
2·
· ^{(VOUT) · (VIN(MAX) - VOUT)}
3
L · F_S · V_IN(MAX)
=¹
2·
3
·
3.3V · (4.2V - 3.3V)
3.3µH · 1.4MHz · 4.2V
= 44mArms
P_esr = esr · I_RMS2 = 5mΩ · (44mA)² = 9.8µW
Input Capacitor
Input Ripple V_PP = 50mV
C_IN =
1
=
V_{PP - ESR}
I_O1 + I_O2
· 4 · F_S
1
= 11.9µF; use 2x10µF
50mV
1.4A
- 5mΩ
· 4 · 1.2MHz
I = _RMS(MAX)
I_O
2
= 1.25Arms
P = esr · I_RMS2 = 5mΩ · (1.25A)² = 6.25mW
2153.2008.09.1.0
www.analogictech.com
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