AVDD is an abbreviation for Analog Psu.
Other names that are sometimes used for the term AVDD are:
• VAA
• VS(A)
• VDDA
• VMAIN
The AVDD voltage is between 10v to 20v with a current of around 3 to 4A.
For small screens with Vcc input 5v, the AVDD voltage is generally around 12v.
For screens 32 and above with Vcc input 12v, the AVDD voltage is generally around 17v.
The AVDD voltage is generated by a "DC-DC Step-Up" or "BOOST CONVERTER" circuit to increase the Vcc Tcon input voltage. The Boost Converter itself is part of the Multi Psu ic found in the Tcon module which also functions to generate other voltages such as VDD 3.3v, VGH, and VGL. This circuit works similarly to how a high frequency switching regulator works. AVDD output voltage is used to supply:
• Gamma IC
• VGH voltage generator circuit by increasing the AVDD voltage approximately 2x.
The AVDD generator circuit schematic can be found by downloading the Datasheet of the Multi Psu IC used. The AVDD circuit is easily identified by the presence of a switching coil, a large rectifier diode, and several large C SMD filters that are paralleled several times. The diode used is a special diode called a Schottky diode.
The AVDD circuit input receives voltage from the Motherboard via a FUSE which is generally located near the LVDS Connector. Some types of Tcon are sometimes found not directly input to the AVDD generator, but through a kind of on-off SWITCH IC.
The FET on the voltage output path functions to isolate the AVDD voltage from the Boost Converter circuit which works at a high frequency of around 750Khz or more.
Damage to the AVDD Generator.
• AVDD generators are generally equipped with Over Voltage Protector and Over Current Protector circuits.
• If the output load is short or half short, the DC Multi Psu IC will turn off protection, and the VGH and VGL voltages will also turn off protection.
• Conversely, if the VGH or VGL voltage is off protection, then the AVDD will also turn off protection.
• If the AVDD voltage and others are off protection, then the VDD 3.3v voltage will not be protected.
• If the measured AVDD voltage is the same as the input Tcon voltage, this indicates that the dc-dc step-up is not functioning, or the IC is damaged.
• AVDD voltage drops or turns off protection (zero voltage) can be caused by one of the C smd output filter sections being short, or the gamma IC being damaged.
Loss of AVDD voltage or input Tcon voltage on old type panels usually results in a blank white screen. On the latest models, the screen is usually blank and dark.