SwitchReg TM
Figure 5: AAT1184ITP Evaluation Board Figure 6: AAT1184ITP Evaluation Board Top Layer. Bottom Layer.
Specifications
V OUT = 5.0V @ 1.2A, Pulsed Load ΔI LOAD = 1.2A
V IN = 12V F S = 490kHz
T AMB = 85°C in TSOPJW-12 Package
Output Inductor
For TDK inductor SLF7045T-4R7M2R0-PF , 4.7μH, DCR = 30m Ω max.
ΔI = · 1 - = · 1 - = 1.2A
I PK = I OUT + = 1.2A + 0.6A = 1.8A
P L1 = I OUT 2
· DCR = 1.8A 2 · 11.7m Ω = 37.9mW
V OUT L 1 · F S ΔI
2
5V 4.7μH · 490kHz Output Capacitor
V DROOP = 0.33V (10% Output Voltage)
5.0V · (24V - 5.0V) 4.7μH · 490kHz · 24V RMS(MAX)I L · F S · V IN1(MAX)3 · ΔI LOAD V DROOP · F S
3 · 1.2A
0.33V · 490kHz C OUT =
== 22.3μF; use 22μF · = 496mA RMS V OUT
· (V IN(MAX) - V OUT1)P RMS = ESR · I RMS 2 = 5m Ω · (496mA)
2 = 1.2mW
Input Capacitor
Input Ripple V PP
= 25mV
C IN =
=
= 32μF
For low cost applications, a 100μF/25V electrolytic capacitor in parallel with a 1μF/25V ceramic capacitor is used to reduce the ESR.
I
OUT 2
RMS I P = ESR · (I RMS )2 = 5m Ω · (0.6A)2 = 1.8mW
== 0.6A