Tool/software:
Hi team,
Is there a defined start-up sequence and shutdown sequence for this device, respectively?
I am concerned about any conditions that could destroy it.
Best Regards,
Ryu.
Hey Ryu,
To have a seamless power on or off scheme on LM4950, pay attention to the HW cfg and signal path to the shutdown pin.
Page 18 of the DS describes a 'micro-power shutdown' feature controlled by the Shutdown pin. It is easy to toggle between power on and off as long as certain requirements are met. The shutdown pin voltage should range between 2V to Vdd/2. To power down the IC, a proper GND connection must be made to turn it off. A low enough GND path to this pin should allow about 40uA to 80uA through the Shutdown pin as 'Isd'. I have attached an image below from the DS. If this requirement isn't met, the device would not respond to a shutdown request and act abnormally. The micro power section explores different shutdown pin configurations you can consider. Powering on could be just as simple as flipping a switch or toggling between the hi and lo states.
Other things to consider are the Cybass and Cin values. In the "optimizing click and pop reduction performance" section, the right combination would ensure less click and pop noise during shutdown or power up. You want a high enough Cbypass cap and small Cin cap to reflect the closed loop gain you are targeting in your application. There is also info on how the selection of Cbypass can affect turn on time. I have attached images below.
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Expected Isd; appropriate high and low states for the Shutdown pin.
How to select Cin and Cbypass correctly.
Turn on time based off Cybypass.
Hope this was informative. While we're here, please share your end equipment and customer.
Regards,
Ore.
