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LV49821VH

For Portable Electronic Device Use 1.4W × 2ch BTL Power Amplifier

ON Semiconductor 

Usage Note

LV49821VH

1. Input coupling capacitor (C1 and C2)

C1 and C2 are input coupling capacitors that are used to cut the DC component. The input coupling capacitors C1, C2

and the input resistors R1 and R3 make up the high-pass filter, attenuating the bass frequency. Therefore, the

capacitance value must be selected with due consideration of the cut-off frequency.

The cut-off frequencies are expressed by the following formulas.

1ch  fc1 = 1/(2π × C1 × R1)

2ch  fc2 = 1/(2π × C2 × R3)

This capacitor affects the pop sound at startup. Note with care that increasing the capacitance value lengthens the

charging time of the capacitor, which will make the pop sound louder.

2. BTL voltage gain

The voltage gain of the first amplifier is determined by the ratio between the resistors R1 and R2 (R3 and R4).

1ch  Vg1 = 20 × log(R2/R1) …unit: dB

2ch  Vg2 = 20 × log(R4/R3) … unit: dB

Therefore, the BTL voltage gain is expressed by the following formulas.

1ch  VgBTL1 = 6 + 20 × log(R2/R1) … unit: dB

2ch  VgBTL2 = 6 + 20 × log(R4/R3) … unit: dB

The BTL voltage gain must be set in the range of 0 to 26 dB.

3. Beep signal input pin (pin 3)

This pin is connected to the non-inverting input block of the first amplifier of the BTL amplifier, and is biased

internally by a 50kΩ resistor. The input coupling capacitor C4 and the bias resistor make up a high-pass filter that

attenuates bass band signals, so when determining the C4 capacitance value, the value must be set with due

consideration of the cut-off frequency. The cut-off frequency is expressed by the following formula.

fc3 = 1/(2π× C4 × 50000)

In addition, when input from Pin 3, the BTL voltage gain is expressed by the following formulas.

1ch  VgBTL1 = 6 + 20 × log(1+R2/(R1 + ro)) … unit: dB

2ch  VgBTL2 = 6 + 20 × log(1+R4/(R3 + ro)) … unit: dB

When setting the signal level, the signal should be attenuated and input as shown in Fig.1.

When not using this input pin, connect it to pin 4 as shown in Application Circuit Example-2.

other IC

OUT

ro

LV49821VH

13

C1

R2

1

R1

C4

3

Beep signal in

4

C3

VREF

Fig.1

4. pin 4 capacitor (C3)

This capacitor is a ripple filter capacitor. The internal resistors (100kΩ + 450kΩ) and C3 make up a low-pass filter that

is used to reduce the power supply ripple component and increase the ripple rejection ratio.

Note that inside the IC, the rising-transient-response-characteristic of the pin 4 voltage (reference voltage) is used to

activate the automatic pop sound reduction circuit. Therefore, when reducing the C3 capacitance value to increase the

voltage rise speed, the design should take into account that the pop sound increases during voltage rise.

5. Power supply line capacitor (C7and C8)

The bypass capacitor C8 is used to remove the high frequency component that cannot be eliminated by the power

supply capacitor C7 (chemical capacitor). Place the bypass capacitor C8 as near to the IC as possible, and use a

ceramic capacitor with good high frequency characteristics.

When using a stabilized power supply, these capacitors can also be combined into a single 2.2μF ceramic capacitor.

Note that when the power supply line is relatively unstable, the power supply capacitor C7 capacitance value must be

increased.

No.A1468-7/15

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