Myrra builds on the success of the 47000 series with the new AC/DC converter series 48000. Let’s check some of its features in the given example.
Converter has to supply electronic device with micro controller with nominal supply voltage of 3.3V. Ambient temperature range is -20 to 80?C. Current consumption is 20uA in sleep mode, max consumption is 250mA.
We have two options in this case: using model 48021 or 48022 + linear or switching voltage regulator 5/3.3V.
Model 48021
1. output voltage accuracy: E1 = ?5%
2. output voltage load regulation: E2 = ?5%
3. dynamic response, 50-100% load change: ?10% rated output voltage
4. output voltage line regulation: E3 = ?5%
5. ripple & noise: 200mV p-p.
Microcontroller?s maximal operating voltage is typically 3.6V, absolute max voltage is typically 4V. Voltage higher than 4V can damage the microcontroller.
In the worst case scenario, DC output voltage can be 3.3V + E1 + E2 + E3 = 3.795V > 3.6V. When we add ?0.33V overshoots and ripple 200mV p-p, output voltage can reach 4.325V > 4V.
Brief worst case analysis has shown us that model 48021 is not suitable for our device.
Model 48022 + Voltage Regulator 5/3.3V
This variant is more expensive but it will certainly meet all requirements. We need to determine if we are going to use linear or switching voltage regulator 5/3.3V. Linear regulator is cheaper but are we able to provide adequate heatsink for it?
In the worst case, DC output voltage of 48022 can be Vout=5V + E1 + E2 + E3= 5 + 5% + 5% + 3% = 5.65V. Power dissipation at max current consumption 250mA is 0.25*(5.65 ? 3.3) =0.59W.
Let?s consider max chip (junction) temperature 105?C to avoid overheating of components in the close vicinity of the regulator. For ambient temperature 80?C, we need the thermal resistance between the junction and the environment to be less than (105-80)/0.59=42.4K/W. When we use regulator housed in WDFN-6 with exposed pad (thermal resistance between junction and pad 5.4K/W), we will need approximately 13.5cm2 of 4-layer PCB (AN-2020 Thermal Design By Insight, Not Hindsight).
In this case, it is not necessary to use switching voltage regulator, PCB required for cooling the linear regulator is acceptable. This solution is therefore technically feasible.
If you are interested in 48000 Series or in any of Myrra products, or you need more information, we are ready to help at myrra@soselectronic.com
