Diodes PAM8908 User Manual

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25mW TRUE CAP FREE STEREO HEADPHONE AMPLIFIER

Description

The PAM8901 / PAM8908 stereo headphone driver is designed for
portable equipment where board space is at a premium. The
PAM8901 / PAM8908 uses a unique, patent pending architecture to
produce a ground-referenced output from a single supply, eliminating
the need for large DC-blocking capacitors, saving cost, board space,
and component height.

The PAM8901 / PAM8908 delivers up to 25mW per channel into a
16Ω load and has low 0.03% THD+N. A high power-supply rejection
ratio (80dB at 1kHz) allows this device to operate from noisy digital
supplies without an additional linear regulator.

The PAM8901 / PAM8908 operates from a single supply from 2.5V t o

5.5V, has short-circuit and over temperature protection. Shutdown
mode reduces supply current to less than 1µA.

Features

• Patent Pending 3 Phase Power Line Shift Charge Pump
Eliminates Need for DC-Blocking Capacitors

• TrueCapFree Architecture, Output Biased at 0V (System
Ground)

• Excellent Low Frequency Fidelity

• 80dB PSRR at 1kHz

• Less than 1uA Shutdown current

• Support both Fully differential and Single-Ended Inputs

• Short Circuit and Over Temperature Protection

• Selectable Gain settings:-6dB,0dB,3dB and 6dB

• Available in Space Saving Packages: TQFN3x3-16L

Typical Applications Circuit

Typical Applcation Configuration with Differential Input Signals

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Pin Assignments

Applications

• Smart Phones/Cellular Phones

• Notebook Computers

• Portable DVD Player

• Personal Digital Assistants (PDAs )

• Electronic Dictionaries

• Digital Still Cameras

• Portable Gaming

PAM8901 / PAM8908

PAM8901/

PAM8908

PAM8901 / PAM8908

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Typical Applications Circuit (cont.)

Typical Applcation Configuration with Single-Ended Input Signal

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PAM8901 / PAM8908

PAM8901/

PAM8908

Pin Descriptions

Pin Number

PAM8901 PAM8908

1
2
3
4
5

1 INL-
2 INL+
3 INR+
4 INR-
6 G0

6 7 G1 I
7

5 OUTR

8 8 HPVSS P

9 10 PGND P
10 9 CAP- O
11 11 CAP+ O
12 14 PVDD P Power V
13 12 HPVDD O Positive power supply for headphone amplifiers. Charge pump positive half V
14 16 OUTL O
15 15 SGND I
16 13 EN I

PAM8901 / PAM8908

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T-QFN3x3-16L

Pin Name

I/O/P Function

Inverting left input for differential signals.

I

Non-inverting left input for differential signals.

I

Inverting right input for differential signals.

I

Non-inverting right input for differential signals.

I

Gain select bit 0

I

Gain select bit 1
Right headphone amplifier output. Connect to right terminal of headphone jack.

O

Charge pump output and negative power supply for output amplifiers; connect 1µF
capacitor to GND

Power Ground
Charge pump negative flying cap.
Charge pump positive flying cap.

.

DD

Left headphone ampli fier output. Connect to left terminal of headphone jack.
Amplifier reference voltage.
Amplifier enabled. Connect to logic low to shutdown; connect to logic high to activate

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Functional Block Diagram

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PAM8901 / PAM8908

Absolute Maximum Ratings (@T

These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may
affect device reliability. All voltages are with respect to ground.

Parameter Rating Unit

Supply Voltage (PVDD)
Input Voltage (INR+, INR-, INL+, INL-)
Control Interface Voltage (G0, G1, EN)
Storage Temperature -65 to +150
Maximum Junction Temperature 150

Soldering Temperature 250, 10sec

= +25°C, unless otherwise specified.)

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Recommended Operating Conditions (@T

Parameter Rating Unit

Supply Voltage Range 2.5 to 5.5 V
Ambient Temperature Range -40 to +85

Junction Temperature Range -40 to +125

6.0 V

HPV

-0.3 to HPVDD +0.3

SS

-0.3 to PV

= +25°C, unless otherwise specified.)

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+0.3

V
V

°C

°C

Thermal Information

Parameter Symbol Package Max Unit

Thermal Resistance (Junction to Ambient)
Thermal Resisitance (Junction to Case)

θ

JA

θ

JC

PAM8901 / PAM8908

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TQFN3x3-16 35 °C/W
TQFN3x3-16 14 °C/W

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Electrical Characteristics (@T

Parameter Symbol Test Conditions Min Typ Max Units

Supply Voltage
Quiescent Current

Output Power per Channel
Shutdown Current

EN High Level Input Voltage VIH 1.4 V
EN Low Level Voltage VIL 0.6 V
G0, G1 High Level Input Voltage VGH 1.4 V
G0, G1Low Level Voltage VGL 0.6 V
Output Offset Voltage

Closed-Loop Voltage Gain AV

Power Supply Rejection Ratio PSRR Input A C-GND, f + 1KHz, VPP = 200mV 75 dB
Total Harmonic Distortion Plus Noise THD+N PO = 20mW, f = 1kHz 0.03 %
Signal to Noise Ratio SNR PO = 20mW, into 16Ω 100 dB
Noise Output Voltage EN A-Weighted 10
Crosstalk CS PO = 15mW, f = 1kHz 80 dB
Chargepump Switching Frequency

Start-Up Time
Thermal Shutdown OTP Threshold 150 °C
Thermal Shutdown Hystersis OTPH Hysteresis 20 °C

PAM8901 / PAM8908

Document number: DSxxxxx Rev. 1 - 1

= +25°C, PVDD = 3.6V, RL = 16Ω unless otherwise specified.)

A

PV

V

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I

Q

P
I

SD

OS

OSC

t

ON

DD

EN = PVDD, No Load
THD = 1%, f = 1kHz, R

O

THD = 1%, f = 1kHz, RL = 32Ω 25 mW
EN = 0V, PVDD = 2.5V to 5.5V 0.1 1 µA

1 5 mV

G0 =0V, G1 = 0V -6 dB
G0 =PVDD, G1 = 0V 0 dB
G0 =0V, G1 = PVDD 3 dB
G0 =PVDD, G1 = PVDD 6 dB

1.2 1.5 1.8 MHz
EN from low to high 0.4 Ms

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= 16Ω 35

L

2.5 5.5 V
4 mA

µV

RMS

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Typical Performance Characteristics (@T

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PAM8901 / PAM8908

= +25°C, PVDD=3.6V, f =1kHz, Gain = 6dB, unless otherwise specified.)

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PAM8901 / PAM8908

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Typical Performance Characteristics (cont.) (@T

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PAM8901 / PAM8908

=+25°C, PVDD=3.6V, f =1kHz, Gain=6dB, unless otherwise specified.)

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PAM8901 / PAM8908

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Typical Performance Characteristics (cont.) (@T

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PAM8901 / PAM8908

= +25°C, CIN=10µF, CO=10µF, L=4.7µH, unless otherwise specified.)

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PAM8901 / PAM8908

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Application Information

The basic PAM8901 / PAM8908 application circuit is shown in page 1 and page 2.

Gain Control

The PAM8901 / PAM8908 has four gain settings which are controlled with pins G0 and G1. The following table gives an overview of the gain
function.

G0 Voltage G1 Voltage Amplifier Gain

≤0.6V ≤0.6V -6dB
≥1.4V ≤0.6V 0dB
≤0.6V ≥1.4V 3dB
≥1.4V ≥1.4V 6dB

Input Coupling Capacitors

Input coupling capacitors block any DC bias from the audio source and ensure maximum dynamic range. Input coupling capacitors also minimize
PAM8901 / PAM8908 turn-on pop to an inaudible level. The input capacitors are in series with PAM8901 / PAM8908 internal input resistors,
creating a high-pass filter. The following Equation calculates the highpass filter corner frequency.

1

The input impedance, RIN, is dependent on device gain. Larger input capacitors decrease the corner frequency. See the following table for input
impedance values.

G0 Voltage G1 Voltage

For a given high-pass cutoff frequency, the minimum input coupling capacitor is found as:

=

f

C

TT

R2

≤0.6V ≤0.6V 26.4kΩ
≥1.4V ≤0.6V 19.8kΩ
≤0.6V ≥1.4V 16.5kΩ
≥1.4V ≥1.4V 13.2kΩ

=

C

IN

TT

C

IN

IN

R

IN

1

Rf2

INC

Example: Design for a 20Hz corner frequency with a PAM8901 / PAM8908 gain of +6dB. The input impedance table gives RIN as 13.2kΩ. The C
Equation shows the input coupling capacitors must be at least 0.6µF to achieve a 20Hz highpass corner frequency. Choose a 0.68µF standard
value capacitor for each PAM8901 / PAM8908 input (X5R material or better is required for best performance).

IN

Charge Pump Flying Capacitor, HPVDD Capacitor and HPVSS Capacitor

The PAM8901 / PAM8908 uses a built-in charge pump to generate a positive and negative voltage supply for the headphone amplifiers. The
charge pump flying capacitor connects between CAP+ and CAP-. It transfers charge to generate the positive and negative supply voltage. The
HPVDD capacitor or HPVSS capacitor must be at least equal in or larger than value to the flying capacitor to allow maximum charge transfer.
Use low equivalent-series-resistance (ESR) ceramic capacitors (X5R material or better is required for best performance) to maxi mize charge
pump efficiency. Typical values are 1µF for the HPVDD, HPVSS and flying capacitors.

Power Supply Decoupling Capacitors

The PAM8901 / PAM8908 TrueCapFree headphone amplifier requires adequate power supply decoupling to ensure that output noise and total
harmonic distortion (THD) remain low. Use good low equivalent-series-resistance (ESR) ceramic capacitors (X5R material or better is required
for best performance). Place a 2.2µF capacitor within 5mm of the PVDD pin. Reducing the distance between the decoupling capacitor and PVDD
minimizes parasitic inductance and resistance, improving PAM8901 / PAM8908 supply rejection performance. Use 0402 or smaller size
capacitors if possible.

Power Supply Sequencing

Use input coupl ing capaci tors to ensure inaudible turn-on pop. Activate the PAM8901 / PAM8908 after all audio s ources have been activated
and their output voltages have settled. On powerd own, deactivate the PAM8901 / PAM8908 before deactivating the audio input source. The EN
pin controls device shutdown: Set to 0.6V or lower to deactivate the PAM8901 / PAM8908; set to 1.4V or higher to activate.

PAM8901 / PAM8908

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Application Information (cont.)

TrueCapFree Headphone Amplifiers

The TrueCapFree amplifier architecture operates from a single supply voltage and uses two internal charge pumps to generate a positive supply
and a rail for the headphone amplifier. The output voltages are centered around 0V and are capable of positive and negative voltage swings as
shown in the following drawing.

TrueCapFree amplifiers require no output DC-blocking capacitors. The headphone connector shield pin connects to ground and will interface
with headphones and non-headphone accessories. The PAM8901 / PAM8908 is a TrueCapFree amplifier.

LAYOUT RECOMMENDATIONS

Exposed Pad on PAM8901 / PAM8908

Solder the exposed metal pad on the PAM8901 / PAM8908 TQFN package to the landing pad on the PCB. Connect the landing pad to ground or
leave it electrically unconnected (floating). Do not connect the landing pad to PVDD or to any other power supply voltage.If the pad is grounded,
it must be connected to the same ground as the PGND. Soldering the thermal pad is required for mechanical reliability and enhances thermal
conductivity of the package.

GND Connections

The SGND pin is an input reference and must be connected to the headphone ground connector pin. This ensures no turn-on pop and minimizes
output offset voltage. Do not connect more than ±0.3V to SGND.
PGND is a power ground. Connect supply decoupling capacitors for PVDD, HPVDD, and HPVSS to PGND.

Power Supply Connections

Connect the supply voltage to the PVDD pin and decouple it with an X5R or better capacitor. Place both PVD D capacitor within 5mm of PVDD
pin on the PAM8901 / PAM8908. Ensure that the ground connection of PVDD capacitor has a minimum length return path to the dev ice. Failure
to properly decouple the PAM8901 / PAM8908 may degrade audio or EMC performance.

PAM8901 / PAM8908

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Ordering Information

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PAM8901 / PAM8908

Part Number Package Type Standard Package

PAM8901JER TQFN3x3-16L 3000 Units/ Tape & Reel
PAM8908JER TQFN3x3-16L 3000 Units/ Tape & Reel

Marking Information

PAM8901 / PAM8908

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Package Outline Dimensions (All dimensions in mm.)

TQFN3x3mm-16

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PAM8901 / PAM8908

Notes: 1. Controlling dimensions are in millimeters (angles in degrees).

2. Coplanarity applies to the exposed pad as well as the terminals.

3. DAP is 1.90 x 1.90mm.

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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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IMPORTANT NOTICE

LIFE SUPPORT

PAM8901 / PAM8908

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