TIOL111: Power issue

Hi Harsh,

The TIOL111 has two supply pins that can be powered in any order, but requires both to be present for proper operation. There is a known behavior with this device is both supplies are not properly supplied.

There are three versions of the TIOL111where two of them output the internal LDO voltage, and the other version uses an externally supplied voltage on the VCC_IN pin.  The core design of all these three devices is basically the same except in the use of the LDO and how some internal signals are referenced through pullup resistors, etc.  The issue comes in how the device determines what version it is and whether to enable the internal LDO or use an external voltage on the VCC_IN pin.

The TIOL111 (non-LDO) version of the device has an internal connection between the VCC_IN pin and a version selection node.  If the device detects a voltage on this node, then it will disable the LDO and use the external voltage on the VCC_IN pin.

The TIOL1113 and TIOL1115 versions do not have this connection to the version selection node since the VCC_IN is now an output of the internal LDO voltage.  Therefore, the digital core will see this version node as floating and enable the LDO.

When the TIOL111 VCC_IN pin is left unpowered while VCC is powered, the device will NOT detect a voltage on the internal version node and enable the LDO just as if this was a TIOL1113/5 device.  As the LDO powers up, the enable signal will go low and cause the LDO enable signal to oscillate between On and Off until the VCC_IN voltage is applied.  Since the TIOL111 version is not intended to use the internal LDO, the internal power is being supplied through these various pullup resistors and the frequency of oscillation will be dependent on the load capacitance on the VCC_IN pin.  Varying the capacitance will change the RC constant.  If you add more capacitance to the VCC_IN pin, it will take longer to charge and therefore the internal voltage thresholds will take longer to cross causing a slower oscillation.  Observing this pin with an oscilloscope will display a waveform that resembles a sawtooth.  If measured with a voltage meter, the average value of the voltage will be returned and read close to the 1V you are reporting.

The TIOL111 was not intended to be functional or used in applications where only one supply is active at a time and therefore it assumes that both supplies will be supplied and active within a short period of time.  The exact timing of how these are supplied is not critical because once a voltage is supplied to the VCC_IN pin, the internal LDO will be disabled.

The voltage threshold output on the VCC_IN pin in this scenario should not exceed 3.46V before it disabled because this is the maximum 3.3V LDO output voltage.  However once it is disabled the voltage will drop until it is approximately 1.1V which is the lower threshold and the LDO will once again be enabled.  Unfortunately this cannot be disabled in the current version of the device.  Adding capacitance will slow this oscillation down until the VCC_IN can be supplied, otherwise you could always use the LDO version of the device to make sure this rail is always powered when VCC is powered.  This could be used independently of the 3.3V or 5V rail you are using for the rest of your board.

I hope this explains the situation you are seeing.

This is being corrected in the next version of the device but the solution is to ensure that both supplies are properly supplied to the device and one of them is not left floating.

Regards,

Jonathan