TDF8599B datasheet(9/54 Pages) NXP

9 / 54 page

NXP Semiconductors

TDF8599B

I2C-bus controlled dual channel 43 W/2 Ohm, single channel 85 W/1 Ohm class-D power amplifier with

load diagnostics

TDF8599B

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 2 — 23 August 2016

9 / 54

8.3.2 Spread spectrum mode (Master mode)

Spread spectrum mode is a technique of modulating the oscillator frequency with a

slowly varying signal to broaden the switching spectrum, thereby reducing the spectral

density of the EMI. Connecting a capacitor (CSSM) to pin SSM enables Spread spectrum

mode (see Figure 6). When pin SSM is connected to pin AGND, Spread spectrum mode

is disabled.

The capacitor on pin SSM (CSSM) sets the spreading frequency when Spread spectrum

mode is active. The current (ISSM) flowing in and out of pin SSM is typically 5 μA.

This gives a triangular voltage on pin SSM that sweeps around the voltage set by pin

OSCSET ± 5 %. The voltage on pin SSM is used to modulate the oscillator frequency.

The spread spectrum frequency (fSSM) can be calculated using Equation 2:

(2)

where the voltage on pin OSCSET = V1 and is calculated as 100 μA × Rosc (V) with

ISSM = 5 μA.

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100 µA

Rosc

SSM

Cosc

OSCSET

a. Off

Figure 6. Spread spectrum mode

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100 µA

5 µA

ISSM

Rosc

SSM

Cosc

CSSM

OSCSET

b. On

The frequency swings between 0.95 × fosc and 1.05 × fosc. See Figure 7.

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t (ms)

OSCIO

max(V)

min(V)

SSM

Figure 7. Spread spectrum operation in Master mode

8.3.3 Frequency hopping (Master mode)

Frequency hopping is a technique used to change the oscillator frequency for AM tuner

compatibility. In Master mode, the resistor connected between pins OSCSET and AGND

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