TDA8920CJ/N1,112 Datasheet TDA8920CTH/N1,118, TDA8920CJ/N1,112 | P7-P9

Product data sheet Rev. 02 — 11 June 2009 7 of 39

NXP Semiconductors

TDA8920C

2 × 110 W class-D power ampliﬁer

To ensure the coupling capacitors at the inputs (C

in Figure 10) are fully charged before

the outputs start switching, a delay is inserted during the transition from Mute to Operating

mode. An overview of the start-up timing is provided in Figure 5. For proper switch-off, the

MODE pin should be forced LOW at least 100 ms before the supply lines (V

DDA

and V

SSA

)

drop below 12.5 V.

(1) First

⁄

pulse down.

Upper diagram: When switching from Standby to Mute, there is a delay of approximately 100 ms

before the output starts switching. The audio signal will become available once V

MODE

reaches the

Operating mode level (see Table 8), but not earlier than 150 ms after switching to Mute. To start-up

pop noise-free, it is recommended that the time constant applied to pin MODE be at least 350 ms

for the transition between Mute and Operating modes.

Lower diagram: When switching directly from Standby to Operating mode, there is a delay of

100 ms before the outputs start switching. The audio signal becomes available after a second

delay of 50 ms. To start-up pop noise-free, it is recommended that the time-constant applied to pin

MODE be at least 500 ms for the transition between Standby and Operating modes.

Fig 5. Timing on mode selection input pin MODE

2.2 V < V

MODE

< 3 V

audio output

operating

standby

mute

50 %

duty cycle

> 4.2 V

0 V (SGND)

time

001aah657

MODE

100 ms

50 ms

modulated PWM

> 350 ms

2.2 V < V

MODE

< 3 V

audio output

operating

standby

mute

50 %

duty cycle

> 4.2 V

0 V (SGND)

time

MODE

100 ms

50 ms

modulated PWM

> 350 ms

(1)

Product data sheet Rev. 02 — 11 June 2009 8 of 39

NXP Semiconductors

TDA8920C

2 × 110 W class-D power ampliﬁer

8.2 Pulse-width modulation frequency

The ampliﬁer output signal is a PWM signal with a typical carrier frequency of between

250 kHz and 450 kHz. A 2nd-order LC demodulation ﬁlter on the output is used to convert

the PWM signal into an analog audio signal. The carrier frequency is determined by an

external resistor, R

OSC

, connected between pins OSC and VSSA. The optimal carrier

frequency setting is between 250 kHz and 450 kHz.

The carrier frequency is set to 345 kHz by connecting an external 30 kΩ resistor between

pins OSC and VSSA. See Table 9 on page 14 for more details.

If two or more class-D ampliﬁers are used in the same audio application, it is

recommended that an external clock circuit be used with all devices (see Section 13.4).

This will ensure that they operate at the same switching frequency, thus avoiding beat

tones (if the switching frequencies are different, audible interference known as ‘beat tones’

can be generated)

8.3 Protection

The following protection circuits are incorporated into the TDA8920C:

• Thermal protection:

– Thermal FoldBack (TFB)

– OverTemperature Protection (OTP)

• OverCurrent Protection (OCP)

• Window Protection (WP)

• Supply voltage protection:

– UnderVoltage Protection (UVP)

– OverVoltage Protection (OVP)

– UnBalance Protection (UBP)

How the device reacts to a fault conditions depends on which protection circuit has been

activated.

8.3.1 Thermal protection

The TDA8920C employes an advanced thermal protection strategy. A TFB function

gradually reduces the output power within a deﬁned temperature range. If the temperature

continues to rise, OTP is activated to shut down the device completely.

8.3.1.1 Thermal FoldBack (TFB)

If the junction temperature (T

) exceeds the thermal foldback activation threshold, the gain

is gradually reduced. This reduces the output signal amplitude and the power dissipation,

eventually stabilizing the temperature.

TFB is speciﬁed at the thermal foldback activation temperature T

act(th_fold)

where the

closed-loop voltage gain is reduced by 6 dB. The TFB range is:

act(th_fold)

− 5 °C < T

act(th_fold)

< T

act(th_prot)

The value of T

act(th_fold)

for the TDA8920C is approximately 153 °C; see Table 8 for more

details.

Product data sheet Rev. 02 — 11 June 2009 9 of 39

NXP Semiconductors

TDA8920C

2 × 110 W class-D power ampliﬁer

8.3.1.2 OverTemperature Protection (OTP)

If TFB fails to stabilize the temperature and the junction temperature continues to rise, the

ampliﬁer will shut down as soon as the temperature reaches the thermal protection

activation threshold, T

act(th_prot)

. The ampliﬁer will resume switching approximately 100 ms

after the temperature drops below T

act(th_prot)

The thermal behavior is illustrated in Figure 6.

8.3.2 OverCurrent Protection (OCP)

In order to guarantee the robustness of the TDA8920C, the maximum output current that

can be delivered at the output stages is limited. OCP is built in for each output power

switch.

OCP is activated when the current in one of the power transistors exceeds the OCP

threshold (I

ORM

= 9.2 A) due, for example, to a short-circuit to a supply line or across the

load.

The TDA8920C ampliﬁer distinguishes between low-ohmic short-circuit conditions and

other overcurrent conditions such as a dynamic impedance drop at the loudspeaker. The

impedance threshold (Z

) depends on the supply voltage.

How the ampliﬁer reacts to a short circuit depends on the short-circuit impedance:

• Short-circuit impedance > Z

: the ampliﬁer limits the maximum output current to I

ORM

but the ampliﬁer does not shut down the PWM outputs. Effectively, this results in a

clipped output signal across the load (behavior very similar to voltage clipping).

• Short-circuit impedance < Z

: the ampliﬁer limits the maximum output current to I

ORM

and at the same time discharges the capacitor on pin PROT. When C

PROT

is fully

discharged, the ampliﬁer shuts down completely and an internal timer is started.

The value of the protection capacitor (C

PROT

) connected to pin PROT can be between

10 pF and 220 pF (typically 47 pF). While OCP is activated, an internal current source is

enabled that will discharge C

PROT

(1) Duty cycle of PWM output modulated according to the audio input signal.

(2) Duty cycle of PWM output reduced due to TFB.

(3) Ampliﬁer is switched off due to OTP.

Fig 6. Behavior of TFB and OTP

001aah656

act(th_fold)

− 5°C)

act(th_fold)

(°C) T

act(th_prot)

Gain

(dB)

30 dB

24 dB

0 dB

12 3

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TDA8920CJ/N1,112

Mfr. #:

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NXP Semiconductors

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TDA8920CJ/N1,112

TDA8920CJ/N1,112

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