Production Data

WM9010

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PD, February 2011, Rev 4.0

7

DEVICE DESCRIPTION

INTRODUCTION

The WM9010 is a low power stereo headphone driver designed for mobile handset and portable

media player (PMP) applications. It is packaged in a 12-pin CSP.

The device comprises two analogue input pins, each accepting line signals up to 1Vrms. The signal

path gain is fixed at 0dB. The headphone output drivers deliver up to 28mW into a 32Ω load.

The WM9010 incorporates Class G technology to achieve high efficiency and low quiescent current.

An integrated charge pump circuit is used to generate the split (positive and negative) power rails

from a single VDD supply. The ground-referenced headphone driver design reduces the device

power consumption and also eliminates external DC-blocking capacitors on the audio output path.

The WM9010 is enabled when a logic high level is detected on ENA. Note that the ENA pin can

support digital logic levels up to 2.7V.

Wolfson’s Silent Switch™ technology is incorporated in order to minimise ‘pop’ noise whenever the

WM9010 is enabled or disabled.

A power on reset circuit ensures correct start-up and shut-down when VDD is switched on or off. The

WM9010 is held in reset when the ENA pin is held low, offering a low-power standby state.

Short circuit and thermal protection is also provided.

HEADPHONE DRIVER

The WM9010 has two analogue input pins, INL and INR. The input signals are referenced to the

INREF pin, which is provided as a quiet ground reference connection. The maximum analogue input

signal level varies with VDD, but is typically 0dBV (1Vrms) when VDD = 1.8V. This is suitable for

single-ended connection to line level input signals.

The headphone output drivers are capable of driving up to 28mW into a 32Ω load such as a stereo

headset or headphones. The outputs are ground-referenced, eliminating any requirement for AC

coupling capacitors. This is achieved by having separate positive and negative supply rails powered

by an on-chip charge pump.

A pop-suppression circuit ensures that DC offsets are minimised, suppressing ‘pop’ noise and

reducing power consumption. To obtain optimal DC offsets, the device should be powered on with no

signal on the input pins.

It is recommended to connect a zobel network to the headphone output pins HPOUTL and HPOUTR

for best audio performance in all applications. The components of the zobel network have the effect

of dampening high frequency oscillations or instabilities that can arise outside the audio band under

certain conditions. Possible sources of these instabilities include the inductive load of a headphone

coil or an active load in the form of an external line amplifier. The capacitance of lengthy cables or

PCB tracks can also lead to amplifier instability. The zobel network should comprise of a 20

Ω resistor

and 100nF capacitor in series with each other, as illustrated in Figure 1.

Figure 1 External Connections for HPOUTL and HPOUTR