DESCRIPTION
These modules are unique in that they combine both a DC-DC converter to accept a wide input voltage range coupled with an LDO linear regulator to provide a well regulated output.
PACKAGE INCLUDES:
- DD38LOSA 3.3V DC-DC / LDO Module
KEY FEATURES OF DD38LOSA 3.3V DC-DC / LDO MODULE:
- 3.3V Output
- 8 to 40V Input
- 700mA continuous current independent of input voltage
- Up to 1A intermittent current
- Short circuit and thermal protection built-in
- Small package compatible with standard 3 pin TO-220 regulator pinout
THEORY OF OPERATION:
The DC-DC input section can take a range of 8 to 40V on its input.
It uses the ME3116 switching regulator IC that operates at 550kHz and is configured to provide a fixed output voltage set to 6.3V. Efficiency of this section is 85-90%.
The 6.3V is then feed to an LDO 1117A-5 linear regulator. This regulator trims the 6.3V down to the final 3.3V output while also helping to filter the ripple and noise on the output of the DC-DC section. Efficiency of this section is 71-78% giving an overall efficiency of 60-70% for the module.
The final output has a ripple of 12-20mV under most conditions. It doesn’t remove it completely due to the tight circuit coupling between the DC-DC converter and linear sections on the small board. It is still 2-10x better than what most DC-DC converters can provide when used alone. Measurements were done with a 100uF bulk capacitor on the output.
Because the linear regulator is always dropping a minimal voltage amount, it can operate at its full 700mA current rating independent of the input voltage.
Module Connections
There is a 3-pin right angle header for making connections.
1 x 3 Header
- I = Vin – Connects to 8 – 40V
- G = Ground
- O = 3.3V output
OUR EVALUATION RESULTS:
These are handy modules that can help resolve some common problems related to trying to generate a fairly clean 3.3V from a relatively high input voltage without having to derate the output current based on the input voltage like when using a linear regulator alone.
We tested these over over the full range of 8 to 40V at 700mA load without any issues. At full load the module does run quite warm as expected.
The modules can handle up to 1A for short periods of time and we have tested to 800mA for extended periods at 25C ambient.
One quirk we have seen in our testing is that if the load is more than 600mA without any bulk capacitance on its output, the output can go into a current limit or other shutdown mode when power is first applied. We have only seen this when testing using electronic dummy loads. Add even a 10uF capacitor on the output resolves this, so it is not expected to be an issue under normal circuit conditions.
One thing to be aware of whenever using any breadboard friendly power module is that while the module may be able to handle 700+mA, the typical breadboard jumper wires will have a fairly significant voltage loss passing that much current. When using with higher current loads you may need to double-up on the wires or use heavier gauge wires on the output voltage connections to minimize the voltage drop.
