TDF8599B datasheet(9/54 Pages) NXP

9 / 54 page

TDF8599B_1

Product data sheet

Rev. 01 — 29 July 2009

9 of 54

NXP Semiconductors

TDF8599B

I2C-bus controlled dual channel class-D power ampliﬁer

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.

The frequency swings between 0.95

× fosc and 1.05 × fosc; see Figure 7.

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

sets the oscillator frequency (fosc). In I2C-bus mode, this frequency can be varied by

± 10 %. Set bit IB1[D4] to logic 1 and bit IB1[D3] to either logic 0 (0.9 × fosc) or logic 1

(1.1

× fosc).

SSM

10 %

------------------------------------------------------ Hz

[]

a. Off

b. On

Fig 6.

Spread spectrum mode

001aai773

100

µA

Rosc

SSM

Cosc

OSCSET

001aai774

100

µA

ISSM

Rosc

SSM

Cosc

CSSM

OSCSET

Fig 7.

Spread spectrum operation in Master mode

001aai775

t (ms)

OSCIO

max(V)

min(V)

SSM

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