UCD74106: Requested information about current monitoring

Do all boards have this issue, or only one board has this issue?

1. If only one board has this issue, check if there is load somewhere else on the board (such as damaged cap, etc.)

2. If all boards have the same issue, it may be related to design or UCD9246 setting.

At zero amp load, the current out of IMON pin should be typically 22.1uA. Please check if it is true. 

(1) If IMON outputs 22.1uA at zero amp load, and Fusion GUI reads 0.5A, the issue is most likely calibration setting in UCD9246. You can calibrate IOUT_CAL_GAIN and IOUT_CAL_OFFSET using Fusion GUI to get correct reading.

(2) If IMON outputs more than 22.1uA at zero load, it may be a UCD74106 issue.

Regards,

Zhiyuan

Hi Zhiyuan,

We got the problem only on few board about 4 at this time.

As mentioned in my previous email; I performed some measure with no load on the P1V0 power supply output and the consumption indicated in the Power Design Tool interface (using the UCD9246 ) is about 500 mA.
In order to perform this measure, the board has been modified by disconnecting the P1V0 from loads.
Only the coil (L304), the capacitor (C305) and the resistor(R302) are kept on the board to produce and monitor the P1V0 power supply (referred to the schematic that I attached on the last email ).

At zero load, the output current is 500mA, so we think that it is an UCD74106 issue; and we would like to know if you can get information explaining this issue.

Moreover, addition information has been transmitted to us by our Production Centre; the UCD74106 has been replaced on one board being in trouble with the over current consumption, after the UCD74106 replacement the consumption come back to the normal one.

Hi Zhiyuan,

We got the problem only on few board about 4 at this time.

As mentioned in my previous email; I performed some measure with no load on the P1V0 power supply output and the consumption indicated in the Power Design Tool interface (using the UCD9246 ) is about 500 mA.
In order to perform this measure, the board has been modified by disconnecting the P1V0 from loads.
Only the coil (L304), the capacitor (C305) and the resistor(R302) are kept on the board to produce and monitor the P1V0 power supply (referred to the schematic that I attached on the last email ).

At zero load, the output current is 500mA, so we think that it is an UCD74106 issue; and we would like to know if you can get information explaining this issue.

Moreover, addition information has been transmitted to us by our Production Centre; the UCD74106 has been replaced on one board being in trouble with the over current consumption, after the UCD74106 replacement the consumption come back to the normal one.

The problem is that the Iout calibration data for the UCD74106 is missing from the UCD9222 configuration file, see GUI reference box below.

If the problem only exists on a few boards then its likely that it was deleted from the configuration of those particular controllers by mistake and reapplying the original configuration file should resolve the issue.

If it is missing from the original configuration file then you can use the information below to recreate it.

The UCD74106 has a built in offset that allows the controller to measure negative current.

From the UCD74106 datasheet:

The Imon pin sources 22.1uA at no load, with the standard 22.6K ohm resistor to ground connected to the Imon pin the resulting offset is ~0.5V .

This information along with the Imon gain of 4.32uA/A is entered into the Fusion GUI for Iout Calibration (if the Design section of the GUI was filled out then this information is automatically populated into the configuration section of the GUI when the Write to Hardware button is pressed).

The GUI performs a bit of math to get the values needed as the PMBus commands require a specific format.

First:  Iout_Cal_Gain is the UCD74106 Imon gain multiplied by the Rcs2 resistance (resistor to ground on Imon pin), 4.32uA/A * 22.6K ohm = 97.6 mV/A or mohm.

Second:  Iout_Cal_Offset is defined as the current when the UCD74106 output is at 0V, which would occur when the Imon output is sourcing 0A into Rcs2.  This would require that rail output would be sinking current into the UCD74106 sufficient to cancel the Imon zero load offset of 22.1uA, (-22.1uA * 22.6K ohm) / 97.6 mohm = -5.117 A.

If you are using a different value for Rsc2 then just substitute in the equations above.

Images were cropped from last response.