MP7720 - Monolithic Power Systems, Inc.

MP7720

20W Class D Mono

Single Ended Audio Amplifer

12/04, Rev. 1.6 www.MonolithicPower.com 1

Monolithic Power Systems

DESCRIPTION

The MP7720 is a mono 20W Class D Audio

Amplifier. It is one of MPS’ second generation

of fully integrated audio amplifiers which

dramatically reduces solution size by integrating

the following:

180m power MOSFETs

Startup / Shutdown pop elimination

Short circuit protection circuits

Mute / Standby

The MP7720 utilizes a single ended output

structure capable of delivering 20W into 4

speakers. MPS Class D Audio Amplifiers exhibit

the high fidelity of a Class A/B amplifier at

efficiencies greater than 90%. The circuit is

based on the MPS’ proprietary variable

frequency topology that delivers excellent

PSRR, fast response time and operates on a

single power supply.

EVALUATION BOARD REFERENCE

Board Number Dimensions

EV0030 2.4”X x 3.5”Y x 1.2”Z

FEATURES

• 20W Output at VDD = 24V into a 4 load

• THD+N = 0.04% at 1W, 8

• 93% Efficiency at 20W

• Low Noise (190µV Typical)

• Switching Frequency Up to 1MHz

• 9.5V to 24V Operation from a Single Supply

• Integrated Startup and Shutdown Pop

Elimination Circuit

• Thermal Protection

• Integrated 180m Switches

• Mute/Standby Modes (Sleep)

• Available in Tiny 8-Pin SOIC and PDIP Packages

APPLICATIONS

• Surround Sound DVD Systems

• Televisions

• Flat Panel Monitors

• Multimedia Computers

• Home Stereo Systems

, “MPS”, “Monolithic Power Systems”, and “The Future of Analog IC

Technology” are Registered Trademarks of Monolithic Power Systems, Inc.

AAM (Analog Adaptive Modulation) is a Trademark of Monolithic Power

Systems, Inc.

TYPICAL APPLICATION

AUDIO

INPUT

OFF ON

MP7720

PGND

VDD

NIN

AGND

MP7720_TAC_S01

0.1

0.01

THD+N (%)

0.1 1 10 30

POWER (W)

MP7720-TPC01

THD+N vs

Power (24V, 1KHz)

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

12/04, Rev. 1.6 www.MonolithicPower.com 2

PACKAGE REFERENCE

NIN

AGND

PGND

VDD

TOP VIEW

MP7720_PD01-SOIC8-PDIP8

Part Number* Package Temperature

MP7720DS SOIC8

–40°C to +85°C

MP7720DP PDIP8

–40°C to +85°C

* For Tape & Reel, add suffix –Z (eg. MP7720DS–Z)

For Lead Free, add suffix –LF (eg. MP7720DS–LF–Z)

ABSOLUTE MAXIMUM RATINGS (1)

Supply Voltage VDD...................................... 26V

BS Voltage.................. VSW – 0.3V to VSW + 6.5V

Enable Voltage VEN........................ –0.3V to +6V

VSW, VPIN, VNIN ........................... –1V to VDD + 1V

AGND to PGND.......................... –0.3V to +0.3V

Junction Temperature............................... 150°C

Lead Temperature ....................................260°C

Storage Temperature ..............–65°C to +150°C

Recommended Operating Conditions (2)

Supply Voltage VDD.......................... 9.5V to 24V

Operating Temperature TA.........–40°C to +85°C

Thermal Resistance (3) θJA θJC

SOIC8.................................... 105 ..... 50... °C/W

PDIP8 ..................................... 95 ...... 55... °C/W

Notes:

1) Exceeding these ratings may damage the device.

2) The device is not guaranteed to function outside of its

operating conditions.

3) Measured on approximately 1” square of 1 oz copper.

ELECTRICAL CHARACTERISTICS

VDD = 24V, VEN = 5V, TA = 25°C, unless otherwise noted.

Parameters Symbol Condition Min Typ Max Units

Supply Current

Standby Current VEN = 0V 1 5 µA

Quiescent Current 1.5 3.0 mA

Output Drivers

SW On Resistance Sourcing and Sinking 0.18 

Short Circuit Current Sourcing and Sinking 5.0 A

Inputs

PIN, NIN Input Common Mode

Voltage Range 0 VDD

2 VDD - 1.5 V

PIN, NIN Input Current VPIN = VNIN = 12V 1 5 µA

EN Rising 1.4 2.0 V

EN Enable Threshold Voltage V

EN Falling 0.4 1.2 V

EN Enable Input Current V

EN = 5V 1 µA

Thermal Shutdown

Thermal Shutdown Trip Point TJ Rising 150 °C

Thermal Shutdown Hysteresis 30 °C

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

12/04, Rev. 1.6 www.MonolithicPower.com 3

OPERATING SPECIFICATIONS

Circuit of Figure 1, VDD = 24V, VEN = 5V, TA = 25°C, unless otherwise noted.

Parameters Symbol Condition Min Typ Max Units

Standby Current VEN = 0V 130 µA

Quiescent Current 13 mA

f = 1KHz, THD+N = 10%,

4 Load 20 W

Power Output

f = 1KHz, THD+N = 10%,

8 Load 10 W

POUT = 1W, f = 1KHz, 4

Load 0.08 %

THD+ Noise

POUT = 1W, f = 1KHz, 8

Load 0.04 %

f = 1KHz, POUT = 1W, 4

Load 90 %

Efficiency

f = 1KHz, POUT = 1W, 8

Load 95 %

Maximum Power Bandwidth 20 KHz

Dynamic Range 93 dB

Noise Floor A-Weighted 190 µV

Power Supply Rejection f = 1KHz 60 dB

PIN FUNCTIONS

Pin # Name Description

1 PIN

Amplifier Positive Input. PIN is the positive side of the differential input to the amplifier. Use a

resistive voltage divider to set the voltage at PIN to VDD/2. See Figure 1.

2 NIN

Amplifier Negative Input. NIN is the negative side of the differential input to the amplifier. Drive

the input signal and close the feedback loop at NIN. See Figure 1.

3 AGND Analog Ground. Connect AGND to PGND at a single point.

4 EN Enable Input. Drive EN high to turn on the amplifier, low to turn it off.

5 BS

High-Side MOSFET Bootstrap Input. A capacitor from BS to SW supplies the gate drive

current to the internal high-side MOSFET. Connect a 0.1µF capacitor from SW to BS. Place a

6.2V zener diode from BS to SW to prevent overstressing of the internal circuitry.

6 VDD

Power Supply Input. VDD is the drain of the high-side MOSFET switch, and supplies the

power to the output stage and the MP7720 internal control circuitry. In addition to the main

bulk capacitor, bypass VDD to PGND with a 1µF X7R capacitor placed close to pins 6 and 8.

7 SW

Switched Power Output. SW is the output of the MP7720. Connect the LC filter between SW

and the output coupling capacitor. See Figure 1.

8 PGND Power Ground. Connect PGND to AGND at a single point.

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

12/04, Rev. 1.6 www.MonolithicPower.com 4

TYPICAL PERFORMANCE CHARACTERISTICS

POUT (W)

5 101520253035

VDD (V)

MP7720-TPC10

OUT

100

EFFICIENCY (%)

0 5 10 15 20 25 30

OUTPUT POWER (W)

MP7720-TPC09

Efficiency vs

OUT

-2

-4

-6

-8

-10

AMPLITUDE (dBr)

20 10K 40K1K100

FREQUENCY (Hz)

MP7720-TPC08

Frequency Response

(Ref=2Vrms, A

=8.2)

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

AMPLITUDE (dBr)

100 1K 10K

FREQUENCY (Hz)

MP7720-TPC07

-20

-40

-60

-80

-100

-120

-140

AMPLITUDE (dBV)

20 100 1K 10K

FREQUENCY (Hz)

MP7720-TPC06

THD+N (%)

FREQUENCY (Hz)

MP7720-TPC05

100

0.1

0.01

THD+N (%)

20 100 1K 10K

FREQUENCY (Hz)

MP7720-TPC04

THD+N (%)

POUT (W)

MP7720-TPC03

0.1

0.01

0.1

0.01

THD+N (%)

0.1 1 10 30 0.1 1 10 30

POUT (W)

MP7720-TPC02

f=1KHz

f=10KHz f=10KHz

f=100Hz f=100Hz

f=1KHz

100

0.1

0.01

20 100 1K 10K

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

12/04, Rev. 1.6 www.MonolithicPower.com 5

OPERATION

The MP7720 is a single-ended Class D audio

amplifier. It uses the Monolithic Power Systems

patented Analog Adaptive ModulationTM to

convert the audio input signal into pulses.

These pulses drive an internal high-current

output stage and, when filtered through an

external inductor-capacitor filter, reproduce the

input signal across the load. Because of the

switching Class D output stage, power

dissipation in the amplifier is drastically reduced

when compared to Class A, B or A/B amplifiers

while maintaining high fidelity and low

distortion.

The amplifier uses a differential input to the

modulator. PIN is the positive input and NIN is

the negative input. The common mode voltage

of the input is set to half the DC power supply

input voltage (VDD/2) through the resistive

voltage divider formed by R2 and R3. The input

capacitor C1 couples the AC signal at the input.

The amplifier voltage gain is set by the

combination of R1 and R4 and is calculated by

the equation:

AV −

The output driver stage uses two 180m

N-Channel MOSFETs to deliver the pulses to

the LC output filter which in turn drives the load.

To fully enhance the high-side MOSFET, the

gate is driven to a voltage higher than the

source by the bootstrap capacitor between SW

and BS. While the output is driven low, the

bootstrap capacitor is charged from VDD through

an internal circuit on the MP7720. The gate of

the high-side MOSFET is driven high from the

voltage at BS, forcing the MOSFET gate to a

voltage higher than VDD and allowing the

MOSFET to fully turn on, reducing power loss in

the amplifier.

Pop Elimination

The capacitor C9 passes only AC currents to

the load. To insure that the amplifier passes low

frequency signals, the time constant of

C9*RLOAD needs to be long. However, when EN

is asserted, the capacitor charges over a long

period and in a normal amplifier can result in a

turn on and/or turn off “pop.” The MP7720

includes integrated circuitry that eliminates the

turn on and turn off pop associated with the

charging of the AC coupling capacitor.

Short Circuit/Overload Protection

The MP7720 has internal overload and short

circuit protection. The currents in both the high-

side and low-side MOSFETs are measured and

if the current exceeds the 5.0A short circuit

current limit, both MOSFETs are turned off. The

MP7720 then restarts with the same power up

sequence that is used for normal starting to

prevent a pop from occurring after a short

circuit condition is removed.

Mute/Enable Function

The MP7720 EN input is an active high enable

control. To enable the MP7720, drive EN with a

2.0V or greater voltage. To disable the

amplifier, drive it below 0.4V. While the MP7720

is disabled, the VDD operating current is less

than 5µA and the output driver MOSFETs are

turned off. The MP7720 requires approximately

500ms from the time that EN is asserted (driven

high) to when the amplifier begins normal

operation.

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

12/04, Rev. 1.6 www.MonolithicPower.com 6

APPLICATION INFORMATION

COMPONENT SELECTION

The MP7720 uses a minimum number of

external components to complete a Class D

audio amplifier. The circuit of Figure 1 is

optimized for a 24V power supply and a 1.5V

RMS maximum input signal. This circuit should

be suitable for most applications. However, if

this circuit is not suitable, use the following

sections to determine how to customize the

amplifier for a particular application.

Setting the Voltage Gain

The maximum output voltage swing is limited by

the power supply. To achieve the maximum

power out of the MP7720 amplifier, set the gain

such that the maximum input signal results in

the maximum output voltage swing.

The maximum output voltage swing is ±VDD/2.

For a given input signal voltage, where VIN(pk)

is the peak input voltage, the maximum voltage

gain is:

)pk(V2

)MAX(A

V×

This voltage gain setting results in the peak

output voltage approaching it’s maximum for

the maximum input signal. In some cases the

amplifier is allowed to overdrive slightly,

allowing the THD to increase at high power

levels, and so a higher gain than AV (max) is

required.

Setting the Switching Frequency

The idle switching frequency is a function of

VDD, the capacitor C3 and the feedback resistor

R4. Lower switching frequencies result in more

inductor ripple, causing more quiescent output

voltage ripple and increasing the output noise

and distortion. Higher switching frequencies

result in more power loss. The optimum

quiescent switching frequency is approximately

600KHz to 700KHz. Refer to the Operating

Specifications for recommended values.

Table 4: Switching Frequency vs. Integrating

Capacitor and Feedback Resistor (see Figure 1)

Gain

(V/V)

Gain

(dB)

(Ω)

(Ω) C3 F

SW VDD

(V)

3.9 15.0 39k 10k 6.8nF 660KHz 12

8.2 18.3 82k 10k 3.3nF 660KHz 12

8.3 21.5 39k 4.7k 6.8nF 660KHz 12

12.0 21.6 120k 10k 2.2nF 610KHz 12

17.4 24.8 82k 4.7k 3.3nF 660KHz 12

25.5 28.1 120k 4.7k 2.2nF 610KHz 12

5.6 15.0 56k 10k 8.2nF 670KHz 24

8.2 18.3 82k 10k 5.6nF 720KHz 24

11.9 21.5 56k 4.7k 8.2nF 670KHz 24

12.0 21.6 120k 10k 4.7nF 620KHz 24

17.4 24.8 82k 4.7k 5.6nF 720KHz 24

25.5 28.1 120k 4.7k 4.7nF 620KHz 24

33.0 30.4 330k 10k 1.8nF 700KHz 24

Choosing the LC Filter

The Inductor-Capacitor (LC) filter converts the

pulse train at SW to the output voltage that

drives the speaker. Typical values for the LC

filter are shown in Figure 1, 10µH inductor and

0.47µF capacitor.

The characteristic frequency of the LC filter

needs to be high enough to allow high

frequency audio to the output, yet needs to be

low enough to filter out high frequency products

of the pulses from SW. The characteristic

frequency of the LC filter is:

()

LC2

The voltage ripple at the output is approximated

by the equation:

⎟

⎠

⎞

⎜

⎝

⎛

×≅

DDRIPPLE f

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

12/04, Rev. 1.6 www.MonolithicPower.com 7

The quality factor (Q) of the LC filter is

important. If this is too low, output noise will

increase, if this is too high, then peaking may

occur at high signal frequencies reducing the

passband flatness. The circuit Q is set by the

load resistance (speaker resistance, typically

4 or 8). The Q is calculated as:

Q00 ××π=×ω=

ω0 is the characteristic frequency in radians per

second and f0 is in Hz. Use an LC filter with Q

between 0.7 and 1

The actual output ripple and noise is greatly

affected by the type of inductor and capacitor

used in the LC filter. Use a film capacitor and

an inductor with sufficient power handling

capability to supply the output current to the

load. The inductor should exhibit soft saturation

characteristics. If the inductor exhibits hard

saturation, it should operate well below the

saturation current. Gapped ferrite, MPP,

Powdered Iron, or similar type toroidal cores

are recommended. If open or shielded bobbin

ferrite cores are used for multi-channel designs,

make sure that the start windings of each

inductor line up (all starts going toward SW pin,

or all starts going toward the output) to prevent

crosstalk or other channel-to-channel

interference.

Output Coupling Capacitor

The output AC coupling capacitor C9 serves to

block DC voltages and thus passes only the

amplified AC signal from the LC filter to the

load. The combination of the coupling capacitor,

C9 and the load resistance results in a first-

order high-pass filter. The value of C9 should

be selected such that the required minimum

frequency is still allowed to pass. The output

corner frequency (-3dB point), fOUT, can be

calculated as:

9CR2

LOAD

OUT ××π×

Set the output corner frequency (fOUT) at or

below the minimum required frequency.

The output coupling capacitor carries the full

load current, so a capacitor should be chosen

such that its ripple current rating is greater than

the maximum load current. Low ESR aluminum

electrolytic capacitors are recommended.

Input Coupling Capacitor

The input coupling capacitor C1 is used to pass

only the AC signal at the input. In a typical

system application, the source input signal is

typically centered around the circuit ground,

while the MP7720 input is at half the power

supply voltage (VDD/2). The input coupling

capacitor transmits the AC signal from the

source to the MP7720 while blocking the DC

voltage. Choose an input coupling capacitor

such that the corner frequency (fIN) is less than

the passband frequency. The corner frequency

is calculated as:

1C1R2

fIN ××π×

Power Source

For maximum output power, the amplifier circuit

requires a regulated external power source to

supply the power to the amplifier. The higher

the power supply voltage, the more power can

be delivered to a given load resistance,

however if the power source voltage exceeds

the maximum operating voltage of 24V, the

MP7720 may sustain damage. The power

supply rejection of the MP7720 is excellent

(typically 60dB), however noise at the power

supply can get to the output, so care must be

taken to minimize power supply noise within the

pass-band frequencies. Bypass the power

supply with a large capacitor (typically

aluminum electrolytic) along with a smaller 1µF

ceramic capacitor at the MP7720 VDD supply

pins.

Circuit Layout

The circuit layout is critical for optimum

performance and low output distortion and

noise. Place the following components as close

to the MP7720 as possible:

Power Supply Bypass, C5

C5 carries the transient current for the switching

input stage. To prevent overstressing of the

MP7720 and excessive noise at the output,

place the power supply bypass capacitor as

close to pins 6 (VDD) and 8 (PGND) as

possible.

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

12/04, Rev. 1.6 www.MonolithicPower.com 8

Output Catch Diode, D1

D1 carries the current over the dead-time while

both MOSFET switches are off. Place D1

between pins 7 (SW) and 8 (PGND) to prevent

the voltage at SW from swinging excessively

below ground.

Input Modulator Capacitor, C3

C3 is used to set the amplifier switching

frequency and is typically on the order of a few

nanofarads. Place C3 as close to the differential

input pins (1 and 2) as possible to reduce

distortion and noise.

Reference Bypass Capacitor, C2

C2 filters the ½ VDD reference voltage at the

PIN input (pin 1). Place C2 as close to PIN as

possible to improve power supply rejection and

reduce distortion and noise at the output.

Use two separate ground planes, analog

ground (AGND) and power ground (PGND),

and connect the two grounds together at a

single point to prevent noise injection into the

amplifier input to reduce distortion. Power

components (C5, D1, C6 and C8) connect to

the power ground. The quiet analog

components (C2, C3, R2, and the input source

ground) connect to the analog ground.

Place the input and feedback resistors R1 and

R4 as close to the NIN input as possible. Make

sure that any traces carrying the switching node

(SW) voltage are separated far from any input

signal traces. If multiple amplifiers are used on

a single board, make sure that each channel is

physically separated to prevent crosstalk. If it is

required to run the SW trace near the input,

shield the input with a ground plane between

the traces. Make sure that all inductors used on

a single circuit board have the same orientation.

If multiple channels are used on a single board,

make sure that the power supply is routed from

the source to each channel individually, not

serially. This prevents channel-to-channel

coupling through the power supply input.

Electro-Magnetic Interference (EMI)

Considerations

Due to the switching nature of the Class D

amplifier, care must be taken to minimize the

effects of electromagnetic interference from the

amplifier. However, with proper component

selection and careful attention to circuit layout,

the effects of the EMI due to the amplifier

switching can be minimized.

The power inductors are a potential source of

radiated emissions. For the best EMI

performance, use toroidal inductors, since the

magnetic field is well contained inside the core.

However toroidal inductors can be expensive to

wind. For a more economical solution, use

shielded gapped ferrite or shielded ferrite

bobbin core inductors. These inductors typically

do not contain the field as well toroidal

inductors, but usually can achieve a better

balance of good EMI performance with low

cost.

The size of high-current loops that carry rapidly

changing currents needs to be minimized. To

do this, make sure that the VDD bypass

capacitor (C5) is as close to the MP7720 as

possible.

Nodes that carry rapidly changing voltage, such

as SW, need to be made as small as possible.

If sensitive traces run near a trace connected to

SW, place a ground shield between the traces.

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

12/04, Rev. 1.6 www.MonolithicPower.com 9

TYPICAL APPLICATION CIRCUIT

AUDIO

INPUT

OFF ON

VDD

9.5V to 24V

MP7720

PGND

VDD

NIN

AGND

MP7720_F01

C10

390pF

6.2V

30V

10pF

5.6nF

Figure 1—20W Mono Typical Application Circuit

MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

NOTICE: MPS believes the information in this document to be accurate and reliable. However, it is subject to change without

notice. Contact MPS for current specifications. MPS encourages users of its products to ensure that third party Intellectual

Property rights are not infringed upon when integrating MPS products into any application. MPS cannot assume any legal

responsibility for any said applications.

MP7720 Rev. 1.6 Monolithic Power Systems, Inc. 10

12/29/04 983 University Avenue, Building A, Los Gatos, CA 95032 USA

PACKAGE INFORMATION

SOIC8

NOTE:

1) Control dimension is in inches. Dimension in bracket is millimeters.

0.016(0.410)

0.050(1.270)

0o-8o

DETAIL "A"

0.011(0.280)

0.020(0.508) x 45

SEE DETAIL "A"

0.0075(0.191)

0.0098(0.249)

0.229(5.820)

0.244(6.200)

SEATING PLANE

0.001(0.030)

0.004(0.101)

0.189(4.800)

0.197(5.004)

0.053(1.350)

0.068(1.730) 0.049(1.250)

0.060(1.524)

0.150(3.810)

0.157(4.000)

PIN 1 IDENT.

0.050(1.270)BSC

0.013(0.330)

0.020(0.508)

PDIP8