EYE ON NPI - Diodes Incorporated PAM8019E Class-D Audio Amplifier and Headphone Driver

Adafruit Industries

This week's EYE ON NPI is loud and proud - it's the Diodes Incorporated PAM8019E Class-D Audio Amplifier and Headphone Driver (https://www.digikey.com/en/product-highlight/d/diodes/pam8019e-class-d-audio-amplifiers), a combo audio amplifier that will add high quality analog audio output to your next design without breaking the bank. We've stocked and used the PAM series of audio amplifiers for over a decade, one of our best sellers is the PAM8302 (https://www.adafruit.com/product/2130) breakout which is a monophonic class D amp for basic projects. Things we like about it: its very inexpensive, it's rock solid, 3~5V power, hard to 'pop' and can drive 4~8 ohm output. But it's only one channel and we often get asked if we can stock a stereo Class D. Also, it's pretty common for us to get requests for headphone drivers. The PAM8019E (https://www.digikey.com/short/b3r00dw5) can do both, and has a lot of nice little details. First up, this is an analog in/out amplifier - no PDM or I2S or TDM. So this is good for either all-analog setups or when you have already converted your digital audio to 'line level', about 1Vpp. Since it's stereo out, there's also stereo input: don't worry about DC bias because you can couple in with 1uF and it will internally bias to half-VDD. Unlike the PAM8302 (https://www.digikey.com/en/products/detail/diodes-incorporated/PAM8302AASCR/4033281), this isn't differential input, reference is ground. You can use either the Headphone amp or Speaker amp, but not both: the selection is done with with a digital input pin which will do a smooth pop-free hand off. For the outputs, there's the stereo Class D outputs. These come as two tied-load bridges (https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers#Bridged_amplifier) which means you can just tie the two sides of each speaker to positive/negative without any capacitors. Class D is an efficient amplification architecture (https://en.wikipedia.org/wiki/Class-D_amplifier) and if done at a high enough frequency - in this case around 400KHz - the inductive load of the speaker acts as a filter so no separate RLC is required. For EMI purposes, the datasheet recommends a simple 100MHz 600ohm ferrite bead plus 1uF capacitor just to reduce the sharp square waves. For headphone, the chip uses a Class AB (https://en.wikipedia.org/wiki/Power_amplifier_classes#Class_AB). These are going to give cleaner output because there's no intermediate PWM stage: speakers tend not to be good enough to notice the hiss added from Class D, but headphones are much more sensitive. Also, at the ~50mW output we're talking about, there's not a lot of benefit to optimizing power. Since headphones are by design 'single ended', you will need 220uF caps on the output for high-pass filtering. Some modern audio amps have a 'floating' ground generated to sink the current for cap-less output but these tend to be more expensive and also wouldn't be compatible with line-level inputs. Some nice details we like to see in an amp, especially one this affordable: spread-spectrum so the high frequency PWM isn't centered on one spike, undervoltage-lockout, short-circuit on all outputs, pop-free, non-clip power limiting and separate not-in-line audio level selection. The last one is particularly nice because on the PAM8302 we have to put an analog rheostat in-line with the input pins to reduce the gain from 15x down to 1x or 2x. This would require a stereo pot, which can get scratchy and fail over time. On the PAM8019E (https://www.digikey.com/short/b3r00dw5), the gain is set with a DC voltage which means you can set it with a potentiometer or a DAC output, and you don't have to worry about jitter or scratchiness because there's hysteresis over 64 points. We've already ordered 10 pieces of the Diodes Inc PAM8019E (https://www.digikey.com/short/b3r00dw5) to design a breakout. DigiKey has tons in stock so we recommend you buy some too, at 34 cents a-piece, at reel quantity, it's hard to say no! They're available in 3x3mm or 4x4mm package sizes, both are QFN-20. Order today and you can be bumpin' and boppin' with either speakers or headphones by tomorrow. afternoon.