MAX4410 Datasheet, PDF(15/20 Page) Maxim Integrated Products – 80mW, DirectDrive Stereo Headphone Driver with Shutdown

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MAX4410 Datasheet, PDF (15/20 Pages) Maxim Integrated Products – 80mW, DirectDrive Stereo Headphone Driver with Shutdown

◁

80mW, DirectDrive Stereo Headphone Driver

with Shutdown

Powering Other Circuits from a

Negative Supply

An additional benefit of the MAX4410 is the internally

generated, negative supply voltage (-VDD). This voltage

is used by the MAX4410 to provide the ground-refer-

enced output level. It can, however, also be used to

power other devices within a design. Current draw from

this negative supply (PVSS) should be limited to 5mA,

exceeding this will affect the operation of the head-

phone driver. The negative supply voltage appears on

the PVSS pin. A typical application is a negative supply

to adjust the contrast of LCD modules.

When considering the use of PVSS in this manner, note

that the charge-pump voltage at PVSS is roughly pro-

portional to -VDD and is not a regulated voltage. The

charge-pump output impedance plot appears in the

Typical Operating Characteristics.

Component Selection

Gain-Setting Resistors

External feedback components set the gain of the

MAX4410. Resistors RF and RIN (see Typical Application

Circuit) set the gain of each amplifier as follows:

ï£«

â ï£ï£¬

RIN

ï£¶

ï£¸ï£·

To minimize VOS, set RF equal to 10kâ¦. Values other

than 10kâ¦ increase VOS due to the input bias current,

which in turn increases the amount of DC current flow

to the speaker.

Compensation Capacitor

The stability of the MAX4410 is affected by the value of

the feedback resistor (RF). The combination of RF and

the input and parasitic trace capacitance introduces an

additional pole. Adding a capacitor in parallel with RF

compensates for this pole. Under typical conditions

with proper layout, the device is stable without the

additional capacitor.

Input Filtering

The input capacitor (CIN), in conjunction with RIN, forms a

highpass filter that removes the DC bias from an incom-

ing signal (see Typical Application Circuit). The AC-cou-

pling capacitor allows the amplifier to bias the signal to

an optimum DC level. Assuming zero-source impedance,

the -3dB point of the highpass filter is given by:

â3dB=

2ÏRINCIN

Choose RIN according to the Gain-Setting Resistors sec-

tion. Choose the CIN such that f-3dB is well below the

lowest frequency of interest. Setting f-3dB too high affects

the low-frequency response of the amplifier. Use capaci-

tors whose dielectrics have low-voltage coefficients,

such as tantalum or aluminum electrolytic. Capacitors

with high-voltage coefficients, such as ceramics, may

result in increased distortion at low frequencies.

Other considerations when designing the input filter

include the constraints of the overall system and the

actual frequency band of interest. Although high-fidelity

audio calls for a flat-gain response between 20Hz and

20kHz, portable voice-reproduction devices such as

cellular phones and two-way radios need only concen-

trate on the frequency range of the spoken human voice

(typically 300Hz to 3.5kHz). In addition, speakers used

in portable devices typically have a poor response

below 150Hz. Taking these two factors into considera-

tion, the input filter may not need to be designed for a

20Hz to 20kHz response, saving both board space and

cost due to the use of smaller capacitors.

Charge-Pump Capacitor Selection

Use capacitors with an ESR less than 100mâ¦ for opti-

mum performance. Low-ESR ceramic capacitors mini-

mize the output resistance of the charge pump. For

best performance over the extended temperature

range, select capacitors with an X7R dielectric. Table 1

lists suggested manufacturers.

Flying Capacitor (C1)

The value of the flying capacitor (C1) affects the load

regulation and output resistance of the charge pump. A

C1 value that is too small degrades the deviceâs ability

to provide sufficient current drive, which leads to a loss

of output voltage. Increasing the value of C1 improves

load regulation and reduces the charge-pump output

resistance to an extent. See the Output Power vs.

Charge-Pump Capacitance and Load Resistance

graph in the Typical Operating Characteristics. Above

2.2ÂµF, the on-resistance of the switches and the ESR of

C1 and C2 dominate.

Table 1. Suggested Capacitor Manufacturers

SUPPLIER

PHONE

FAX

Taiyo Yuden

800-348-2496

847-925-0899

TDK

847-803-6100

847-390-4405

Note: Please indicate you are using the MAX4410 when contacting these component suppliers.

WEBSITE

www.t-yuden.com

www.component.tdk.com

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