System

VDD

XSMT

7.25kO

2.75kO

12V

supply

0.9 * DVDD

0.1 * DVDD

2.0 V

1.2 V

XSMT

Digital Attenuation Followed by Analog Mute

Analog Mute

PCM5100, PCM5101, PCM5102

www.ti.com

SLAS764

– MAY 2011

External Power Sense Undervoltage Protection mode

The XSMT pin can also be used to monitor a system voltage, such as the 24VDC LCD TV backlight, or 12VDC

system supply using a potential divider created with two resistors. (See Figure 35 )

•

If the XSMT pin makes a transition from

“1” to “0” over 6ms or more, the device will switch into external

under-voltage protection mode. In this mode, two trigger levels are used.

•

When XSMT pin level reaches 2V, soft mute process begins.

•

When XSMT pin level reaches 1.2V, analog mute will engage, regardless of digital audio level, and analog

shut down will begin. (i.e. DAC circuitry will power down etc).

A timing diagram to show this is shown in Figure 36.

NOTE

The XSMT input pins voltage range is from -0.3V to DVDD + 0.3V.The ratio of external

resistors must be considered within this input range. Any increase in power supply (such

as power supply positive noise/ripple) can pull the XSMT pin higher than DVDD+0.3V.

For example, if the PCM510x is monitoring a 12V input, and dividing the voltage by 4, then the voltage at XSMT

during ideal power supply conditions will be 3V. If the voltage spikes any higher than 14.4V, then XSMT will see

a voltage in excess of 3.6V (DVDD+0.3), potentially damaging the device.

Providing the divider is set appropriately, any DC voltage can be monitored.

Figure 35. XSMT in External UVP Mode

Figure 36. XSMT Timing for Undervoltage Protection

Copyright

© 2011, Texas Instruments Incorporated

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