TDF8541JSSLASHN2 datasheet(11/54 Pages) NXP

11 / 54 page

TDF8541

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Product data sheet

Rev. 3 — 13 December 2011

11 of 54

NXP Semiconductors

TDF8541

I2C-bus controlled 4

 45 W power amplifier

switched off. If several channels have a short across the load at the same time, the

channels are switched on one by one to prevent high supply current switching with four

shorts across the load at the same time. The 15 ms cycle reduces power dissipation. To

prevent audible distortion, the channel with the short can be disabled via the I2C-bus.

7.4.2 Loss-of-ground/loss of VP

Loss-of-ground/loss of VP is a double fault condition: the ground (or VP) wire of the set is

not connected and the ground (or VP) wire is connected to one of the loudspeaker

outputs. In this situation the supply capacitor in the set is charged through the body diode

of the output power transistor. This body diode (between the drain and source of the

power transistor) is always present in amplifiers with MOS output stages. The capacitor

charge current depends on the series impedance of the supply lines, the output

impedance of the loss-of-ground tester and the value of the capacitor; see Figure 7. To

simulate a worst-case condition, the loss-of-ground tester is equipped with a buffer

capacitor of 116 mF to simulate a very low output impedance. With a RS of 63 m, peak

currents of more than 70 A have been measured.

(1) Capacitor can be 2200

F to 10000 F.

(2) Amplifier output stage.

Fig 7.

Test circuit for loss-of-ground test

Cbuffer

116 mF

NMOS

80N03L

2200 μF

Vpulse

(1)

(2)

001aam695

Loss-of-ground tester

DUT in application

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