About the SSM2211 operating voltage

Hello Tsuyoshi -san,

First I need to mention that this part was designed a very long time ago! The first release date is 2002 so 23 years ago! This means it was designed before that!

There is nobody around who was part of that design team that I can ask questions to. I took a look at the datasheet and I will use my experience being on design teams and characterizing parts to supply some answers but a lot of this is my observations and opinions. 

Everywhere in the datasheet the operating voltages are between 2.7V and 5V. This tells me that this was the intended operational range. They did characterize it some to a lower voltage because it was designed for battery operation. So hence the chart in figure 46. 

According to that chart the part will put out around 100mW of power at 1.8V. That is super small!!! 

This part seems to be to be entirely analog with only the shutdown pin being somewhat of a logic function. So I suspect it would work fine to power up and initialize at 1.8V. The performance should align with the graph in figure 46. 

But, I worry with most of the datasheet talking about the min Vbat voltage is 2.7V that running it lower than that most of the time is questionable. 

We have other class-D amps. Shall I refer you over to one of our engineers who works on those parts more than I? 

Are you tying to operate the amp from a 1.8V power supply that is available on some designs? 

You can also contact our local Field Engineers close to you and they can help you work out a design? Then you can share what your application is. 

Thanks,

Dave T  

Hello Dave-san,

Thank you very much for your prompt and detailed reply.
For your reference, I am a DFAE based in Japan.

To give you some background, our customer is currently considering a competitor's 1W Class AB amplifier,
and operation at a low voltage (around 2.0V) was mentioned as a key benefit for their application.
Based on this, I considered the SSM2211 with its similar architecture as the first candidate,
which is why I inquired about its low-voltage operation.
I will share this information with the customer,
making it clear that it is for their reference and represents your expert view.

However, I have received additional information that the customer plans to use this amplifier only for driving a buzzer. Therefore, I now also plan to propose the MAX9705 (Class D amp) as an alternative.
Although its minimum operating voltage is 2.5V, its high efficiency and ultra-low EMI are very attractive for this application.

I will reconfirm with the customer what their specific performance requirements are around 2.0V.
If any further questions arise after that, I will reach out to you again.

Thank you again for your support.

Best regards,
Tsuyoshi Tokumoto

The cleanest answers I can provide are:

1) Can the SSM2211 reliably power on and initialize correctly
     if the supply voltage VDD is 1.8V at the moment of startup?

MN=>Since it is a linear amplifier, it likely can operate at 1.8V.  The performance however is not guaranteed as we are deviating from the rated voltage.  The supply voltage rating not only includes design simulation and measured results on bench and ATE, but it also accounts for variation in the fab process and temperature.  So, it might work just fine outside of rated supply voltage, but you could also encounter a situation a year or more later where the part might not behave as expected.

This is the answer I must provide to anyone wanting to operate our parts outside of rated conditions.  We simply can't guarantee performance or long-term reliability.

2) If it can successfully start up at 1.8V, can we expect its amplifier
    performance to align with the trend shown in Figure 46 of the datasheet?

MN=> Yes, this is just Ohm's law.  While there is some minor output impedance, otherwise, the output power is just a function of V^2/R.

Hello Mike-san,

Thank you very much for your clear and definitive answers regarding the SSM2211.
I greatly appreciate you taking the time to provide such a detailed technical explanation.

I clearly understand your official position: while the SSM2211 may function at 1.8V,
its performance and long-term reliability cannot be guaranteed outside of the rated conditions.
This is a very important clarification for us.

Based on your advice, I will inform my customer that operating the SSM2211
at 1.8V is not a recommended solution and carries a reliability risk.

I truly appreciate your excellent support.

Best regards,
Tsuyoshi Tokumoto