8
FN6458.2
October 17, 2007
Detailed Description
The Intersil ISL54000, ISL54001, ISL54002 family of devices
are integrated audio power amplifier systems designed to
drive 8 speaker loads. They can operate with a supply
voltage of +2.7V to +5V and provide good quality audio, while
requiring minimal external components. Its low 0.4% THD+N
while driving 800mW into an 8 speaker ensures clean, low
distortion amplification of the audio signals. The devices are
offered in a 20 Ld 4x4 TQFN package. Targeted applications
include handheld equipment such as cell-phones, MP3
players, and games/toys.
The ISL54000, ISL54001, ISL54002 parts contain two class
AB bridge-tied (BTL) type power amplifiers for driving stereo
8 speakers. When powered with a 5V supply, each BTL is
capable of delivering 941mW (typ) of continuous average
power to an 8speaker load with 1% THD+N performance.
When the speaker load is connected across the positive and
negative terminals of the BTL driver, the voltage is doubled
across the load and the power is quadrupled.
The ISL54001 and ISL54002 feature a 2:1 stereo input
multiplexer front-end. This allows selection between two
stereo sources. The INS control pin determines which stereo
input is active. Applying a logic “0” to the INS control pin
selects stereo input 1 (R
1
and L
1
). Applying a logic “1” to the
INS control pin selects stereo input 2 (R
2
and L
2
).
The ISL54002 has the capability of mixing the two stereo
inputs. When in MIX Mode (MIX = “1”) the ISL54002 mixes
the R
1
input with the R
2
input and sends the combined
signal to the OUTR_ BTL driver and it mixes the L
1
input
with the L
2
input and sends the combined signal to the
OUTL_ BTL driver.
All devices in this family feature low power shutdown,
thermal overload protection and click/pop suppression. The
click and pop circuitry prohibits switching between input
channels until the audio input signals are at their lowest
point, which eliminates audible transients in the speakers
when changing 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 on page 6 and 7.
DC Bias Voltage
The ISL54000, ISL54001, ISL54002 have internal DC bias
circuitry, which DC offsets the incoming audio signal at
V
DD
/2. When using a 5V supply, the DC offset will be 2.5V.
When using a 3.6V supply, the DC offset will be 1.8V.
Since the signal gets biased internally at V
DD
/2, the audio
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
0.22
µF will pass a signal as low as 7.2Hz. The formula
required to calculate the capacitor value is shown in
Equation 1:
The 100k
is the impedance looking into the input of the
ISL54000, ISL54001, and ISL54002 devices.
BTL Speaker Amplifiers
The ISL54000, ISL54001, and ISL54002 contain two
bridge-tied load (BTL) amplifiers designed to drive a speaker
load differentially. The output from one BTL is OUTL+ and
OUTL-. The output of the other BTL is OUTR+ and OUTR-.
A single BTL driver consists of 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
OUTL+ and OUTL- have the same amplitude but are 180°
out-of-phase. The same is true of OUTR+ and OUTR-. The
speaker load gets connected between the + terminal and
- terminal outputs.
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.
The outputs of each BTL are biased at V
DD
/2. When the
load 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.
Low Power Shutdown
With a logic “1” at the SD control pin the device enters the
low power shutdown state. When in shutdown the output
amplifiers go into an high impedance state and supply
current is reduced to 26
µA (typ).
In shutdown mode before the amplifiers enter the high
impedance/low current drive state, the bias voltage of V
DD
/2
remains connected at the output through a 100k resistor.
This resistor is not present during active operation of the
drivers but gets switched in when the SD pin goes high and
disconnected when the SD pin goes low.
Leaving the DC bias voltage connected through this 100k
resistor reduces the transient that is generated across the
speaker, while going into or out of shutdown, to a level that
does not produce clicking or popping in the speaker.
QFN Thermal Pad Considerations
The QFN package features an exposed thermal pad on its
underside. This pad lowers the package’s thermal resistance
by providing a direct heat conduction path from the die to the
PCB. Connect the exposed thermal pad to GND by using a
(EQ. 1)
C 1 6.28 f 100k
ISL54000, ISL54001, ISL54002
