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AN4233 Datasheet(PDF) 3 Page - STMicroelectronics |
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AN4233 Datasheet(HTML) 3 Page - STMicroelectronics |
3 / 12 page AN4233 Description Doc ID 024143 Rev 1 3/12 1 Description As mentioned, this test methodology allows measuring with high accuracy Rth j-a of the Sound Terminal® amplifier when it is assembled in a PCB. 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. High precision resistor (Rsense): four sense resistors with very low resistive value (for instance 0.1 Ω) must be connected in series between each output and the load. These will be used to read the current (Iout = VRsense/Rsense) 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 across each sense resistor. This equipment will be used to measure VRsense and Vout. 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, |
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