AAT1185 Datasheet, PDF (14/16 Pages) Skyworks Solutions Inc. – High Voltage Step-Down Controller

DATA SHEET
AAT1185
High Voltage Step-Down Controller
AAT1185 Design Example
Specifications
V_O = 3.3V @ 10A, Pulsed Load I_LOAD = 10A
V_IN = 12V
F_S = 490kHz
T_AMB = 85°C in TSOPJW-14 Package
Output Inductor
For Epcos inductor B82559A0392A013, 3.9μH, DCR = 4.8m max.
ΔI
=
V_OUT
L₁ · F_S
·
1-
V_OUT
V_IN
=
3.3V
· 1 - ^3.3V
3.9μH · 490kHz
12V
= 1.25A
ΔI
I_PK1 = I_OUT1 + ₂ = 10A + 0.6A = 10.6A
P_L1
=
I²
OUT1
·
DCR
=
10.6A²
·
4.8mΩ
=
539mW
Output Capacitor
V_DROOP = 0.6V
C_OUT =
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 10A _{= 102μF; use 2x47μF}
0.6V · 490kHz
I_RMS(MAX)
=
1
2·
3
·
V_OUT · (V_IN(MAX) - V_OUT)
L · F_S · V_IN(MAX)
=¹ ·
2· 3
3.3V · (24V - 3.3V)
3.9μH · 490kHz · 24V
= 430mA_RMS
P_RMS = ESR · I_RMS2 = 5mΩ · (430mA)² = 0.9mW
Input Capacitor
Input Ripple V_PP = 60mV
C_IN =
1
=
V_PP
I_OUT
- ESR
· 4 · F_S
1
= 510μF
60mV
10A
- 5mΩ
· 4 · 490kHz
For low cost applications, a 470μF/25V electrolytic capacitor in parallel with a 10μF/25V ceramic capacitor is used to
reduce the ESR.
I_RMS
=
I_OUT1
2
=
5A
P = ESR · (I_RMS)² = 5mΩ · (5A)² = 125mW
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
14
202001A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 31, 2012