AN4233

Description

Doc ID 024143 Rev 1

3/12

1

Description

To perform the test it is not necessary to modify the hardware in the final application

although some registers must be configured in order to have the appropriate setup of the

device.

Setting the registers to have ternary modulation and with no input signal (or amplitude

< –60 dBFs), each output of the power stage will be set to GND. Connecting the output to a

positive source and with a resistor connected in series to limit the current, it is possible to

sink a DC current from the output. A reliable and cheap method to measure the output

current is to convert the current to voltage using a high-precision sense resistor (for instance

0.1

Ω) connected in series to each output. Using a voltmeter it is possible to also measure

the voltage level on the output of each bridge and this information, along with the current

level, allows calculating with high accurancy the RDSon of each power output (only for the

low-side portion of the output bridge).

1.1

Equipment needed and HW and SW configuration

To perform the measurement, the equipment and the settings are summarized as follows:

Register setting: the device must be set to have TERNARY modulation scheme.

Output loads: four dummy resistors must be connected to each bridge output and

connected to a positive supply voltage (Vdd or Vcc).

Input signal: it must be null or < –60 dBFs.

instance 0.1

Ω) must be connected in series between each output and the load. These

Current meter (DC): a current meter must be inserted in series to each supply

sources; specifically Vdd (+3.3 V) and Vcc must be monitored. The series resistance of

this equipment must be very low to avoid adding any unwanted voltage drop.

Voltmeters (DC): a voltmeter will be used to measure both Vdd and Vcc after the

current meter and to measure the voltage across each sense resistor. The accuracy of

this equipment must be precise enough to measure the low voltage levels present

Thermal camera: a thermal camera must be used to measure the device temperature.

Care must be taken to avoid any possible mistake during the temperature

measurement; it is mandatory to define the right emission coefficient and to avoid

reflection from the device package (special paint could be used or a small portion of

non-reflective tape could be applied on top of the case). It is mandatory to use a

thermal camera with a resolution high enough to discriminate the surface of the device.

It is not recommended to use an IR thermometer because with this tool it is not

possible to measure with sufficient precision the device due to the optical angle and

also the position of the beam.

From the description above it is clear that all the measurements have been performed in the

DC domain. This aspect is very important because whatever parasitic effects due to the

PWM switching signal will be cancelled as well as the losses in the snubber networks,