AAT2522 Datasheet, PDF (17/19 Pages) Skyworks Solutions Inc. – Dual High-Current, Low-Noise, Step-Down Regulator

DATA SHEET
AAT2522
Dual High-Current, Low-Noise, Step-Down Regulator
Step-Down Converter Output Capacitor
V_DROOP = 0.2V
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 2A
0.2V · 1.4MHz
= 21.4μF; use 22μF
I = _RMS(MAX)
1
2·
· ^{VOUT2 · (VIN(MAX) - VOUT2)}
3
L · F_S · V_IN(MAX)
=¹
2·
·
3
1.2V
1.5μH
·
·
(5.5V - 1.2V)
1.4MHz · 5.5V
=
129mA_RMS
P_RMS = ESR · I_RMS2 = 5mΩ · (129mA)² = 83μW
Step-Down Converter Input Capacitor
Input Ripple V_PP = 50mV
C_IN =
1
=
V_PP
I_O
- ESR
· 4 · F_S
1
= 9μF; use 10μF
50mV _{- 5mΩ · 4 · 1.4MHz}
0.2A
I_RMS
=
I_OUT
2
=
1A
P = ESR · (I_RMS2) = 5mΩ · (1A)² = 5mW
AAT2522 Losses
All values assume at 85°C ambient temperature and thermal resistance of 50°C/W in the TDFN34-16 package.
P_TOTAL
=
I_OUT12
·
(R_DS(ON)H
·
V_OUT1 +
V_IN
R_DS(ON)L
·
[V_IN
-V_OUT1])
+
(t_sw
·
F_S
·
I_OUT1
+
I_Q1)
·
V_IN
+
I_OUT22
·
(R_DS(ON)H
·
V_OUT2 +
V_IN
R_DS(ON)L
·
[V_IN
-V_OUT2])
+
(t_sw
·
F_S
·
I_OUT2
+
I_Q2)
·
V_IN
P_{TOTAL =} ^{1A2 · (0.12Ω · 3.3V + 0.085Ω · [3.6V - 3.3V])} _{+ (5ns · 1.4MHz · 1A + 84μA) · 3.6V}
3.6V
+ ^{2A2 · (0.12Ω · 1.2V + 0.085Ω · [3.6V - 1.2V])} + (5ns · 1.4MHz · 2A + 84μA) · 3.6V
3.6V
P_{TOTAL = 0.58W}
T_J(MAX) = T_AMB + Θ_JA · P_LOSS = 85°C + (50°C/W) · 0.58mW = 114°C
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012
17