TDF8591TH datasheet(16/34 Pages) NXP

16 / 34 page

TDF8591TH_1

Product data sheet

Rev. 01 — 5 March 2008

16 of 34

NXP Semiconductors

TDF8591TH

× 100 W SE (4 Ω) or 1 × 310 W BTL (4 Ω) class-D ampliﬁer

Peak output current, internally limited to 12 A:

SE:

BTL:

Variables:

RL = load resistance

Rs(L) = series resistance of the ﬁlter coil

RDSon(hs) = high side drain source on-state resistance (temperature dependent)

RDSon(ls) = low side drain source on-state resistance (temperature dependent)

fosc = oscillator frequency

tw(min) = minimum pulse width (typical 150 ns, temperature dependent)

VP = single sided supply voltage [or 0.5 (VDD + |VSS|)]

Po(0.5%) = output power at the onset of clipping

IOM should be below 12 A (see Section 6.4.3). IOM is the sum of the current through the

load and the ripple current. The value of the ripple current is dependent on the coil

inductance and voltage drop over the coil.

12.3 External clock

If two or more class-D ampliﬁers are used it is recommended that all devices run at the

same switching frequency. This can be realized by connecting all OSC pins together and

feed them from an external oscillator.

The internal oscillator requires an external Rext(OSC) and Cext(OSC) between pins OSC and

VSSA. For application of an external oscillator it is necessary to force OSC to a DC level

above SGND. The internal oscillator is disabled and the PWM modulator will switch with

the external frequency. The duty cycle of the external clock should be between 47.5 %

and 52.5 %.

The noise contribution of the internal oscillator is supply voltage dependent. In low noise

applications running at high supply voltage an external low noise oscillator is

recommended.

12.4 Noise

Noise should be measured using a high-order low-pass ﬁlter with a cut-off frequency of

20 kHz. The standard audio band pass ﬁlters used in audio analyzers do not suppress the

residue of the carrier frequency sufﬁciently to ensure a reliable measurement of the

audible noise. Noise measurements should preferably be carried out using AES 17 (Brick

Wall) ﬁlters or the Audio Precision AUX 0025 ﬁlter, which was designed especially for

measuring switching (class-D) ampliﬁers.

w min

()

–

osc

----------





DSon hs

()

-------------------------------------------------------------

wmin

()

osc

---------

–





DSon hs

()

DSon ls

()

() 2R

()

-------------------------------------------------------------------------------------------

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