MP7758

– 18V, 2x15W, STEREO BTL, INDUCTORLESS CLASS-D AUDIO AMPLIFIER

MP7758 Rev. 1.0

www.MonolithicPower.com

15

12/3/2020

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2020 MPS. All Rights Reserved.

EN

Audio

Signal Input

InAbsence

Output

Signal Detected

Enable

Delay Time

SW

PVCC

Start-

Up

No Input Signal

Detected

signal

Detected

Figure 3: Enable On (Audio Signal Present)

Adjustable Power Limit

The MP7758 features power limiting and anti-

clipping control. The voltage on the PLIMIT pin

can limit the power below levels that would be

possible based on the supply rail.

Connect a resistor divider from AVCC to GND

to set the power limit. Connect the resistor

divider directly to AVCC to remove the power

limit.

An external reference may also be used if

tighter tolerance is required. In this scenario,

place

a 1μF capacitor from PLIMIT to ground.

The PLIMIT circuit sets a limit on the output

peak-to-peak voltage. The is accomplished by

limiting the duty cycle to fixed maximum value.

This limit acts as a virtual voltage rail that is

lower than the supply connected to PVCC. This

virtual rail is 9 times the voltage at the PLIMIT

pin. The output voltage can be used to calculate

the

maximum

output

power

for

a

given

maximum input voltage and speaker impedance

(see Figure 4).

Figure 4: PLIMT Circuit Operation

For unclipped power, the output power can be

calculated with Equation (1):

2

L

P

LS

OUT

L

R

V

R

2 R

P

2R





















(1)

Where RS is the total output series resistance

(including RDS(ON) and the resistance of the

output filter), RL is the load resistance, and VP is

the peak amplifier of the output voltage.

If the PLIMIT voltage times 8 is below the

PVCC voltage, VP can be estimated with

Equation (2):

VP = 9 x PLIMIT Voltage

(2)

The value for clipped output power can be

calculated with Equation (3):

OUT

OUT

P

@10%THD 1.25 unclipped P



(3)

Table 2 lists typical power limit values.

Table 2: Typical Power Limit Operation

Test Conditions

PLIMIT

Voltage

Output

Voltage (VPP)

Output Power

(10% THD)

VDD = 12V, VIN = 1VRMS,

load = 8

Ω, gain = 20dB

0.80V

14.9

5.0W

VDD = 16V, VIN = 1VRMS,

load = 8

Ω, gain = 20dB

0.80V

14.9

5.0W

VDD = 16V, VIN = 1VRMS,

load = 8

Ω, gain = 20dB

1.44V

23.6

10.0W

VDD = 18V, VIN = 1VRMS,

load = 8

Ω, gain = 20dB

1.44V

23.6

10.0W