This repository is intended as a collection of precision power supplies for analog circuitry and noise sensitive applications, such as test and measurement or audio. The general guidelines are:
- Outputs: Bipolar supplies with at least +/- 9V and +/- 100mA output capability.
- Inputs: Support one or more common input voltages / USB-C power delivery output voltages (5V,12V,20V).
- Form factor: Compact layout (small current loops) & low height (to add shielding).
- Components: Avoid exotic or hard to solder parts unless mandatory for good implementation.
- PCB: 2 or 4 layer boards, stay within common manufacturing capabilites (no extra charges).
There are a few dual switcher ICs out there that can be applied in this context such as:
- TPS6513x (2.7V-5.5V Input, f_sw = 1.25MHz, good for battery or USB powered applications)
- LT3471 (2.4-16V Input, f_sw = 1.2MHz, similar to TPS6513x but more versatile and expensive)
- LT8582 (2.5-22V Input, f_sw <= 2.5MHz, very versatile and beefy 3A switches)
- LT8471 (2.6-50V Input, f_sw <= 2MHz, extremely versatile but not quite as beefy as LT8582)
LT3471 and TPS7A39 circuits are basically copied together from the respective datasheets / evaluation boards. This project is specifically aimed at replacing dual 9V batteries in portable projects. The idea is to be able to use any USB power bank that supports USB-PD in a formerly 9V battery powered project while maintaining reasonably low noise and not breaking the bank. Rev 01 / prototype layout is not very optimized but decent enough for 2 Layers, in general quite easy to implement and promising combo of ICs. Linear Technology offers their own split-rail LDO LT3032 that similar to TPS7A39, but it has a split thermal pad which can be annoying during assembly.
Changes for Rev 02:
- Change most 0603 passives to 0402
- Shrink & optimize overall layout
- Make it an easily implemented sub-assembly
LT8582 is a really interesting switcher IC. It features two multitopology DC/DC converters that can each be configured as boost, SEPIC, inverting or flyback regulators. The package however absoltely requires reflow soldering and to achieve a decent layout, extensive use of 0603 or even 0402 passives is as necessary as a 4-Layer PCB. While slightly more challenging to implement properly, this IC is too interesting to pass on, which is why I have decided to first design a prototype with a combination of Cuk and SEPIC topologies. With the goal of maximum miniaturization while avoiding 0402 components and maintaining good layout practices, I came up with this 35x35mm PCB:
It lacks any mounting holes and placing low noise LDOs right next to the inductors would heavily degrade their performance.
On the last page of the LT8471 datasheet datasheet we find another promising candidate: A combination of ZETA and Cuk converters, both of which are low-noise due to the second inductor being in series with the output and the general arrangement of switching and energy storage elements in these topologies.
I have seen few implementations of this application circuit, but it is next in line after a functional prototype of the LT8582 version is completed.