ISL54003, ISL54005, ISL54006

FN6514 Rev 2.00

Page 9 of 16

October 30, 2007

pop circuitry prohibits switching between input channels until

the audio input signals are at there lowest point which

eliminates audible transients in the speakers when changing

the audio input sources. The click/pop circuitry also keeps

speaker transients to an inaudibile level when entering and

leaving shutdown.

“Typical Application Circuits and Block Diagrams” for each

device in the family are provided on page 7 and page 8. Truth

tables for each device are provided on page 3.

DC Bias Voltage

The ISL54003, ISL54005, and ISL54006 have internal DC bias

circuitry, which DC offsets the incoming audio signal at

When using a 3.6V supply, the DC offset will be 1.8V.

signals need to be AC coupled to the inputs of the device. The

value of the AC coupling capacitor depends on the low

frequency range required for the application. A capacitor of

0.22µF will pass a signal as low as 7.2Hz. The formula

required to calculated the capacitor value is shown in Equation

1:

The 100k

 is the impedance looking into the input of the

ISL54003, ISL54004, ISL54006 devices.

BTL Speaker Amplifier

The ISL54003, ISL54005, and ISL54006 contain one

bridge-tied load (BTL) amplifier designed to drive an 8



speaker load differentially. The output to the BTL amplifier are

SPK+ and SPK-. The speaker load gets connected across

these terminals.

A single BTL driver consists of an inverting and non-inverting

power op amps. The AC signal out of each op amp are equal in

magnitude but 180° out-of-phase, so the AC signal at SPK+

and SPK- have the same amplitude but are 180° out-of-phase.

Driving the load differentially using a BTL configuration

doubles the output voltage across the speaker load and

quadruples the power to the load. In effect you get a gain of

two due to this configuration at the load as compared to driving

the load with a single-ended amplifier with its load connected

between a single amplifier’s output and ground.

gets connected across the + and - terminal of the BTL the mid

supply DC bias voltage at each output gets cancelled out

eliminating the need for large bulky output coupling capacitors.

Headphone (Single-Ended) Amplifiers

The ISL54003, ISL54005, and ISL54006 contains two single-

ended (SE) headphone amplifiers for driving the left and right

channels of a 32

 or 16 headphone speaker.

One SE amplifier drives the right speaker of the headphone

and other SE amplifier drives the left speaker of the

headphone. The speaker load gets connected between the

output of the amplifier and ground.

The audio signal at the output of each SE driver is biased at

its differential connection, a capacitor is required at the output

of each SE drivers to remove this DC voltage from the

headphone load.

This coupling capacitor along with the resistance of the

speaker load creates a high pass filter that sets the amplifier’s

lower bandpass frequency limit. The value of this AC coupling

capacitor depends on the low frequency range required by the

application. The formula required to calculate the capacitor

value is shown in Equation 2:

For an application driving a 32

 headphone with a lower

frequency requirement of 150Hz, the required capacitor value

would be determined by using Equation 3:

Use the closest standard value.

Headphone Sense Function

With a logic “1” at the HP control pin while the HO control pin is

low will activate the headphone drivers and disable the BTL

driver.

The “Typical Application Circuits and Block Diagrams” on

page 7 and page 8 show the implementation of the headphone

control function using a common headphone jack.

The HP pin gets connected to the mechanical wiper blade of

the headphone jack. Two external resistors are required for

proper operation. A 100k

 pull-up resistor from the HP pin to

pin to ground of the jack signal pin to which the wiper is

connected. See the block diagrams on page 7 and page 8.

When no headphone plug is inserted into the jack, the voltage

at the HP pin gets set at a low voltage level due to the 10k



resistor and 100k

When a headphone is inserted into the jack, the 10k

 resistor

gets disconnected from the HP control pin and the HP pin gets

drivers are activated.

A microprocessor or a switch can be used to drive the HP pin

rather than using the headphone jack contact pin.

Note: With a logic “1” at the HO pin, the BTL driver remains

active regardless of the voltage level at the HD pin. This allows

a headphone to be plugged into the headphone jack without

activating the HP drivers. Music will continue to play through

the internal 8

 speaker rather than the headphones.

(EQ. 1)

C 1 6.28 f 100k











(EQ. 2)

C 1 6.28 f Rspeaker









(EQ. 3)

C 1 6.28 150 32

33

F

=







