1/20

STA575

July 2003

MONOCHIP BRIDGE STEREO AMPLIFIER

ON BASH

ARCHITECTURE

80+80W OUTPUT POWER @ R

= 4/8

THD = 0.5%

100+100W OUTPUT POWER @ R

= 4/8

THD = 10%

HIGH DYNAMIC PREAMPLIFIER INPUT
STAGES

EXTERNAL PROGRAMMABLE FEEDBACK
TYPE COMPRESSORS

AC COUPLED INPUT TO CLASS AB BRIDGE
OUTPUT AMPLIFIER

PRECISION RECTIFIERS TO DRIVE THE
DIGITAL CONVERTER

ON-OFF SEQUENCE/ TIMER WITH MUTE
AND STANDBY

PROPORTIONAL OVER POWER OUTPUT
CURRENT TO LIMIT THE DIGITAL
CONVERTER

ABSOLUTE POWER BRIDGE OUTPUT

TRANSISTOR POWER PROTECTION

ABSOLUTE OUTPUT CURRENT LIMIT

INTEGRATED THERMAL PROTECTION

POWER SUPPLY OVER VOLTAGE
PROTECTION

FLEXIWATT POWER PACKAGE WITH 27 PIN

BASH® LICENCE REQUIRED

DESCRIPTION

The STA575 is a fully integrated power module de-
signed to implement a BASH® amplifier when used
in conjunction with STABP01 digital processor.

FLEXIWATT27

100+100W STEREO

POWER AMPLIFIER

BLOCK DIAGRAM

ABSOLUTE

VALUE
BLOCK

OUTPUT BRIDGE

PEAK/2

DETECTOR

VOLTAGE

PROTECTION

SOA

DETECTOR

TURN-

ON/OFF

SEQUENCE

THERMAL

PROTECTION

PEAK/2

DETECTOR

COMPRESSOR

-1

V/l

Ict

ABSOLUTE

VALUE
BLOCK

OUTPUT BRIDGE

CD-2

CD+2

STBY/MUTE

PROT.

CD+

CD-1

OUT1-

OUT1+

CD+1

IN_PRE1

ATT_REL1

TRK_OUT

THRESH

ATT_REL2

IN_PRE2

PWR_INP1

TRK_1

OUT_ PRE1

-VS

GND

+VS

PWR_INP2

D01AU1263

TRK_2

OUT_ PRE2

OUT2-

OUT2+

-1

STA575

2/20

DESCRIPTION (continued)

Notice that normally only one Digital Converter is needed to supply a stereo or multi-channel amplifier system,
therefore most of the functions implemented in the circuit have summing outputs

The signal circuits are biased by fixed negative and positive voltages referred to Ground. Instead the final stag-
es of the output amplifiers are supplied by two external voltages that are following the audio signal . In this way
the headroom for the output transistors is kept at minimum level to obtain a high efficiency power amplifier.

The Compressor circuits, one for each channel, performs a particular transfer behavior to avoid the dynamic
restriction that an adaptive system like this requires. To have a high flexibility the attack / release time and the
threshold levels are externally programmable. The tracking signal for the external digital converter is generated
from the Absolute Value block that rectifies the audio signal present at the compressor output. The outputs of
these blocks are decoupled by a diode to permit an easy sum of this signal for the multichannel application. The
output power bridges have a dedicated input pin to perform an AC decoupling to cancel the compressor output
DC offset. The gain of the stage is equal to 4 (+12dB). A sophisticated circuit performs the output transistor pow-
er detector that , with the digital converter, reduces the power supply voltage . Moreover, a maximum current
output limiting and the over temperature sensor have been added to protect the circuit itself. The external volt-
age applied to the STBY/MUTE pin forces the two amplifiers in the proper condition to guarantee a silent turn-
on and turn-off.

ABSOLUTE MAXIMUM RATINGS

Note 1: V

CD-

must not be more negative than -Vs and V

CD+

must not be more positive than +V

Note 2: All pins withstand

2KV ESD but not pin 11

Symbol

Parameter

Value

Unit

Positive supply voltage referred to pin 13 (GND)

-V

Negative supply voltage referred to pin 13 (GND)

-24

CD+

Positive supply voltage tracking rail referred to pin 13 (GND)

CD+

Positive supply voltage operated to Vs+

(1)

0.3

CD-

Negative supply voltage referred to -Vs

(1)

-0.3

CD-

Negative supply voltage tracking rail referred to pin 13 (GND)

-22

Att_Rel1

Att_Rel2

Pin 3, 25 Negative & Positive maximum voltage referred to GND
(pin 13)

-0.5 to +20

Pwr_Imp1

Pwr_Imp2

Trk_1

Trk_2

Pin 7, 21, 18, 10 Negative & Positive maximum voltage referred to
GND (pin 13)

-20 to +20

In_pre1

In_pre2

Pin 8, 20 Negative & Positive maximum voltage referred to GND
(pin 13)

-0.5 to +0.5

threshold

Pin 17 Negative & Positive maximum voltage referred to GND (pin
13)

-7 to +0.5

stb-max

Pin 11 maximum input current (Internal voltage clamp at 5V)

500

stbymute

Pin 11 negative maximum voltage referred to GND (pin 13)

-0.5

out

Output current

7.7

3/20

STA575

THERMAL DATA

OPERATING RANGE

PIN CONNECTION

Note: Slug connected to pins n. 1 and 27

Symbol

Parameter

Value

Unit

Max Junction temperature

150

°C

th j_case

Thermal Resistance Junction to case

.............................. ..

max

C/W

Symbol

Parameter

Value

Unit

Positive supply voltage

+20 to +28

-V

Negative supply voltage

-10 to -23

Delta positive supply voltage

(Vs+ - VCD+)

10V

CD+

Positive supply voltage tracking rail

+3 to 20.7

CD-

Negative supply voltage tracking rail

-20.7 to -3

in_Max

Current at pin In_Pre1, In_Pre2, related to compressor behaviour

-1 to +1

mA peak

trheshold

Voltage at pin Threshold

-5 to 0

amb

Ambient Temperature Range

0 to 70

°C

sb_max

Pin 11 maximum input current (Internal voltage clmp at 5V)

200

D01AU1251

CD-1

-V

ATT-REL1

OUT1+

OUT1-

CD+1

PWR_INP1

IN_PRE1

OUT_PRE1

TRK_1

STBY/MUTE

PROTECTION

GND

CD+

TRK_OUT

THRESHOLD

TRK_2

OUT_PRE2

IN_PRE2

PWR_INP2

CD+2

OUT2-

OUT2+

ATT_REL2

CD-2

-Vs

STA575

4/20

PIN FUNCTION

N°

Name

Description

-Vs

Negative Bias Supply

CD-1

Channel 1 Time varying tracking rail negative power supply

Att_Rel1

Attack release rate for channel 1

Out1+

Channel 1 speaker positive output

Out1-

Channel 1 speaker negative output

CD+1

Channel 1 positive power supply

Pwr_Inp1

Input to channel 1 power stage

In_pre1

Pre-amp input for channel 1 (virtual ground)

Out_pre1

Output channel 1 pre-amp

Trk_1

Absolute value block input for channel 1

Stby/mute

Standby/mute input voltage control

Protection

Protection signal for STABP01 digital processor

Gnd

Analog Ground

+Vs

Positive Bias Supply

CD+

Time varying tracking rail positive power supply

Trk_out

Reference output for STABP01 digital processor

Threshold

Compressor threshold input

Trk_2

Absolute value block input for channel 2

Out_pre2

Output channel 2 pre-amp

In_pre2

Pre-amp input for channel 2 (virtual ground)

Pwr_Inp2

Input to channel 2 power stage

CD+2

Channel 2 positive power supply

Out2-

Channel 2 speaker negative output

Out2+

Channel 2 speaker positive output

Att_Rel2

Attack release rate for channel 2

CD-2

Channel 2 Time varying tracking rail negative power supply

-Vs

Negative Bias Supply

5/20

STA575

ELECTRICAL CHARACTERISTCS (Test Condition: Vs+ = 28V, Vs- = -23V, V

CD+

= 20V, V

CD-

= -20V, R

, external components at the nominal value f = 1KHz, Tamb = 25°C unless otherwise specified

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

PREAMPLIFIER AND COMPRESSOR

out clamp

Maximum Voltage at Out_pre pin

Vpeak

Audio input current

0.8

control

Voltage at Attack_Release pin

Attenuation = 0dB
Attenuation = 6dB
Attenuation = 26dB

0.35

0.5

0.65

V
V
V

omp_

Input voltage range for the
compression

-5

-1

Input impedance of Threshold pin

100

Voffset

Output Offset at Out_pre pin with:

CRT

= 0V; Attenuation = 0dB

CRT

= 0.5V; Attenuation = 6dB

CRT

= 9V; Attenuation = 26dB

-15

-250

-1000

250
450

mV
mV
mV

THD

Distortion at Out_pre:

CRT

= 0V; Attenuation = 0dB

CRT

= 0.5V; Attenuation = 6dB

CRT

= 9V; Attenuation = 26dB

0.01

0.1
0.5

%
%
%

Noise at Out_pre pin :

CRT

= 0V; Attenuation = 0dB

CRT

= 0.5V; Attenuation = 6dB

CRT

= 9V; Attenuation = 26dB

(2)

50
60

Attack time current at pin
Attack_release

0.5

1.5

1. This value is due to the thermal noise of the external resistors R

and R

TRACKING PARAMETERS

trk

Tracking reference voltage gain

trk_out

Tracking ref. output voltage

trk_out

Current capability

trk_in

Input impedance (T

RK1/2

)

OUTPUT BRIDGE

out

Half Output bridge gain

5.5

6.5

Output bridge differential gain

Output bridges gain mismatch

-0.5

0.5

out

Continuous Output Power

THD = 0.5%
THD = 10%

75
95

100

W
W

THD = 10%; R

= 4

; V

CD+

= 16V;

CD-

= -16V; V

S+

= 22V; V

S-

= -22V

100

THD

Total harmonic distortion of the
output bridge

Po = 5W

0.01

0.1

f = 20Hz to 20KHz; Po = 50W

0.2

Off

Output bridge D.C. offset

-70

STA575

6/20

Noise at Output bridge pins

f = 20Hz to 20KHz; Rg = 50

br_in

Input impedance

100

140

180

dson

Output power Rdson

= 1A

200

400

OLG

Open Loop Voltage Gain

100

Unity Gain Bandwidth

1.4

MHz

Slew Rate

PROTECTION

stby

Stby voltage range

0.8

mute

Mute voltage range

1.6

2.5

play

Play voltage range

First Over temperature threshold

130

°C

Second Over temperature
threshold

150

°C

Unbal.

Ground

Upper Unbalancing ground
threshold

Referred to (CD

- CD

)/2

Unbal.

Ground

Lower Unbalancing ground
threshold

Referred to (CD

- CD

)/2

-5

Under voltage threshold

|Vs+| + |Vs-|

d_reg.

Power dissipation threshold for
system regulation

prot

= 50

A; @ Vds = 10V

d_max

Switch off power dissipation
threshold

@ Vds = 10V

prot

Protection current slope

for Pd > Pd

reg

400

A/W

lct

Limiting Current threshold

6.3

7.5

I+Vs

Positive supply current

Stby (Vstby/mute pin = 0V)
Mute (Vstby/mute pin = 2.5V)
Play (Vstby/mute pin = 5V no signal)

20
20

35
35

50
50

mA
mA
mA

I-Vs

Negative supply current

Stby (Vstby/mute pin = 0V)
Mute (Vstby/mute pin = 2.5V)
Play (Vstby/mute pin = 5V no signal)

20
20

35
35

50
50

mA
mA
mA

ICD+

Positive traking rail supply current

Stby (Vstby/mute pin = 0V)
Mute (Vstby/mute pin = 2.5V)
Play (Vstby/mute pin = 5V no signal)

50
60
60

100
110
110

200
180
180

mA
mA

ICD-

Negative traking rail supply current Stby (Vstby/mute pin = 0V)

Mute (Vstby/mute pin = 2.5V)
Play (Vstby/mute pin = 5V no signal)

50
60
60

100
110
110

200
180
180

mA
mA

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

ELECTRICAL CHARACTERISTCS (continued)

7/20

STA575

FUNCTIONAL DESCRIPTION

The circuit contains all the blocks to build a stereo amplifier. Each single channel is based on the Output Bridge
Power Amplifier, and its protection circuit. Moreover, the compression function and a signal rectifier are added
to complete the circuit.

The operation modes are driven by The Turn-on/off sequence block. In fact the IC can be set in three states by
the Stby/mute pin:

Standby ( V

< 0.8V), Mute (1.6V < V

< 2.5V), and Play (V

> 4V).

In the Standby mode all the circuits involved in the signal path are in off condition, instead

in Mute mode the circuits are biased but the Speakers Outputs are forced to ground potential.

These voltages can be get by the external RC network connected to Stby/Mute pin.

The same block is used to force quickly the I.C. In standby mode or in mute mode when the I.C. dangerous
condition has been detected. The RC network in these cases is used to delay the Normal operation restore.

The protection of the I.C. are implemented by the Over Temperature, Unbalance Ground, Output Short circuit,
Under voltage, and output transistor Power sensing as shown in the following table:

Table 1. Protection Implementation

See the POWER PROTECTION paragraph for the details

Compression

An other important function implemented, to avoid high power dissipation and clipping distortion, is the Com-
pression of the signal input. In fact the preamplifier stage performs a voltage gain equal to 5, fixed by Ri and Rr
external resistor, but in case of high input signal or low power supply voltage, its gain could be reduced of 26dB.
This function is obtained with a feedback type compressor that , in practice, reduces the impedance of the ex-
ternal feedback network. The behavior of compression it's internally fixed but depends from the Audio input volt-
age signal level, and from the Threshold voltage applied to the Threshold pin. The attack and release time are
programmable by the external RC network connected to the Att_Rel pins.

The constraints of the circuit in the typical application are the following:

Vthreshold range

= -5 to 0

Vin peak max

= 8V

Vout peak max

= 10V

Fault Type

Condition

Protection strategy

Action time

Release time

Chip Over
temperature

Tj > 130 °C

Mute

Fast

Slow Related to
Turn_on sequence

Chip Over
temperature

Tj > 150 °C

Standby

Fast

Slow, Related to
Turn_on sequence

Unbalancing
Ground

|Vgnd| > ((CD+) -
(CD-))/2 + 5V

Standby

Fast

Slow, Related to
Turn_on sequence

Short circuit

Iout > 7A

Standby

Fast

Slow, related to
Turn_on sequence

Under Voltage

|Vs+| + |Vs-|< 20V

Standby

Fast

Slow, related to
Turn_on sequence

Extra power
dissipation
at output transistor

Pd tr. > 32W

Reducing DIGITAL
CONVERTER output
voltage.

Related to the
DIGITAL
CONVERTER

Maximum power
dissipation
at output transistor

Pd tr. > 60W

Standby

Fast

Slow, related to
Turn_on sequence

STA575

8/20

Gain without compression (G)

= 5

Max Attenuation ratio

= 26 dB

The following graph gives the representation of the Compressor activation status related to the Vthreshold and
the input voltage. The delimitation line between the two fields, compression or not, is expressed by the formula :

Where G is the preamplifier gain without compression.

In the compression region the gain of the preamplifier will be reduced

(G = 2·Vthreshold/Vin) to maintain at steady state the output voltage equal 2*|Vthreshold| .

Instead in the other region the compressor will be off (G = 5).

The delimitation line between the two fields can be related to the output voltage of the preamplifier: in this case
the formula is :

Figure 1. Compressor activation field

The relative attenuation introduced by the variable gain cell is the following :

The total gain of the stage will be:

Gdb = 20log5 + Attenuation

The maximum input swing is related to the value of input resistor, to guarantee that the input current remain
under Iin_Max value (1 mA).

Vth resho ld

200 mV

(

)

--------------------------------------------------------------------------

out

Vthre sho ld

200m V

(

)

G = 5

|Vthreshold|

PEAK

COMPRESSION

G < 5

D01AU1264

Atten uati on

2
5

---

log

200 m V

(

)

in_peak

------------------------------------------

in_peak

in_max

----------------------

9/20

STA575

Figure 2. Compressor attenuation vs. input amplitude

ABSOLUTE VALUE BLOCK

The absolute value block rectifies the signal after the compression to extract the control voltage for the external
digital converter. The output voltage swing is internally limited, the gain is internally fixed to 14.

The input impedance of the rectifier is very high , to allow the appropriate filtering of the audio signal before the
rectification (between Out_pre and Trk pins).

OUTPUT BRIDGE

The Output bridge amplifier makes the single-ended to Differential conversion of the Audio signal using two
power amplifiers, one in non-inverting configuration with gain equal to 2 and the other in inverting configuration
with unity gain. To guarantee the high input impedance at the input pins, Pwr_Inp1 and Pwr_Inp2, the second
amplifier stages are driven by the output of the first stages respectively.

POWER PROTECTION

To protect the output transistors of the power bridge a power detector is implemented (fig 3).

The current flowing in the power bridge and trough the series resistor Rsense is measured reading the voltage
drop between CD+1 and CD+. In the same time the voltage drop on the relevant power (Vds) is internally mea-
sured. These two voltages are converted in current and multiplied: the resulting current , Ipd, is proportional to
the instantaneous dissipated power on the relevant output transistor. The current Ipd is compared with the ref-
erence current Ipda, if bigger (dissipated power > 32W) a current, Iprot, is supplied to the Protection pin. The
aim of the current Iprot is to reduce the reference voltage for the digital converter supplying the power stage of
the chip, and than to reduce the dissipated power. The response time of the system must be less than 200

Sec

to have an effective protection. As further protection, when Ipd reaches an higher threshold (when the dissipated
value is higher then 60W) the chip is shut down, forcing low the Stby/Mute pin, and the turn on sequence is
restarted.

-24

-18

-12

-6

|Vinpk|

Attenuation(dB)

D01AU1265

|Vth=1|

|Vth=2.5|

|Vth=5|

STA575

10/20

Figure 3. Power Protection Block Diagram

In fig. 3 there is the power protection strategy pictures. Under the curve of the 32W power, the chip is in normal
operation, over 60W the chip is forced in Standby. This last status would be reached if the digital converter does
not respond quikly enough reducing the stress to less than 60W.

The fig.4 gives the protection current, Iprot, behavior. The current sourced by the pin Prot follows the formula:

for P

< P

d_av_th

the I

prot

= 0

Independently of the output voltage, the chip is also shut down in the folowing conditions:

When the currentthrough the sensing resistor, R

sense

, reaches 7A (Voltage drop (CD+) - (CD+1) = 700mV).

When the average junction temperature of the chip reaches 150°C.

When the ground potential differ from more than 5V from the half of the power supply voltage, ((CD+)-(CD-))/2

When the sum of the supply voltage

Vs+

| +

|Vs-| <20V

The output bridge is muted when the average junction temperature reaches 130°C.

V/I

ILOAD

I_PD

SENSE

MULTIPLIER

ILIM

CURRENT COMP

OC1

PDP1

IPROT

TO TURN-ON/OFF
SEQUENCE

TO PROT PAD

D01AU1266

IPDP

IPDA

IPD

V/I

OPA

OUT1-

OUT1+

OPA

CD-

CD+

CD+1

pr ot

d_av _th

)

(

5 10

1.25V

------------------------------------------------------------------

11/20

STA575

Figure 4. Power protection threshold

Figure 5. Protection current behaviour

Vds (V

Ids (

mA)

Pd_reg = 25W

Pd_M ax =

48W

Ilim = 6A

Standby

BucK

Limitation

Normal

Operation

Pd(W)

Iprot(mA)

D01AU1268

Iprot slope=0.4mA/W

Figure 6. Test Circuit for STA575 Stand-alone

INPUT1

IN_PRE1

OUT_PRE1

OUT1+

OUT1-

STBY/
MUTE

TRK_1

PWR_INP1

ATT_REL1

CD+1

CD+

CD+2

R16

R17

R24

C12

C17

R14

R13

R15

MUTE

STBY

R11

INPUT2

IN_PRE2

OUT_PRE2

TRK_2

PWR_INP2

ATT_REL2

C16

R10

R12

-V

GND

R22

R20

C13

C14

C15

C10

C11

CD-1

TRK-OUT

PROT

THRESH

PROT

THRESH

TRK-OUT

CD-2

CD-

R19

R18

OUT2+

OUT2-

D01AU1267

STA575

12/20

EXTERNAL COMPONENTS (refer to fig. 6)

Note: Vcontrol is the voltage at Att_Rel pin.

Name

Function

Value

Formula

R1 = R2

Input resistor

10K

(|G| = 5, Rr = 50K

)

R3 = R4

Feedback resistor

50K

(|G| = 5, Ri = 10K

Cac

C1 = C2

AC Decoupling capacitor

100nF

(fp = 16Hz,

Rac =100K

)

Cct

C3 = C4

Capacitor for the attack time

2.2

(Tattack = 13mSec,

Vcontrol = 9V,

Ict = 1.5mA)

R5 = R6

Release constant time Resistor

470K

(

= 1 Sec. ,

Cct = 2.2

F )

R7 = R8

Resistor for tracking input voltage
filter

10K

R9 = R10

Resistor for tracking input voltage
filter

56K

R11 = R12

Resistor for tracking input voltage
filter

10K

C5 = C6

Capacitor for Tracking input
voltage filter

1nF

C7 = C8

Dc decoupling capacitor

R13

Bias Resistor for Stby/Mute
function

10K

R14

Stby/Mute constant time resistor

30K

R15

Mute resistor

30K

Capacitor for Stby/Mute resistor

2.2

R16 = R17

Sensing resistor for SOA detector

100m

5% 4W

R18

Conversion resistor for threshold
voltage

100K

C10 = C11

Power supply filter capacitor

100nF

R22 = R24

Centering resistor

400

C12 = C13

Tracking rail power supply filter

680nF

R19

Protection

R20

TRK_out

40K

C14 = C15

Power supply filter capacitor

470

63V

C16 = C17

Feedback capacitor

100pF

Schottky diode

SB360

-------

Cac

fp Rac

---------------------------------

Cct

attack

Ict

Vcontrol

-------------------------

Rct

Cct

---------

13/20

STA575

APPLICATION HINTS (refer to fig. 6)

PREAMPLIFIER AND COMPRESSOR

In the test circuit showed in figure 6, R

(or R

) ratio fix the gain of the preamplifier.

If the input signal is very low, is possible to increase the gain fixing the product Vin

G = cost.

In that case is possible to increase G decreasing R

1,2

from 10K

until 2K

without relevant effetcs on the cir-

cuitbehavior and remaining in the operating range I

in_max

= V

in_max

1(2)

,<1mA.

So it is possible to increase the preamplifier gain until 25.

If no compression is present (equivalnt compressor Gm=0), the effects are:

The output voltage offset increase

The SNR decrease

The following table shows these variations:

3(4)

= 50K

and all the other external components are the same

Attenuation = 0 dB

If the compression is active the circuit behaviour is the same.

It"s also possible to eliminate the compressor. In this case the ATT_REL (1,2) pin must be connected to gnd.

STBY-MUTE CIRCUIT

In the suggested application circuit (figure 6), the resistor for Standby/Mute function (R

) is connected between

the Standby/Mute switches and 5V Supply.

It is possible to connect the resistor to another Supply Voltage level V

, but in that case also the resistor value

13,14

) must be changed according to the following formula (fixing V

STBY/MUTE

= 2.5V and R

= 10K

HEADROOM

In the suggested application circuit the supply voltage to obtain 75W (Power Output) on 8

load

)

is:

It is also possible to increase the system's efficiency forcing the headroom to follow the output signal (variable
drop insteadof a constant drop).

In that case:

1,2

IN MAX

OFFSET

10K

15mV

30mV

1.6V

75mV

4 V

(

)

4 V

(

)

suppl y

L M AX

D S on

sup ply

( )

D S on

STA575

14/20

Figure 7. BASH® module SAM351 5.1 with 2 x STA575 (see application note AN1656)

Power - On-Off sequences:

In order to avoid damages to the SAM261 board it is important to follow these sequences:

At Power-On apply in the first the Auxiliary Power Supply (±24V) and after the Main Power Supply
(+50V), in this condition the system is in "Mute state" and it can move in "play state" with the switch present
on the pcb.

At Power-Off is better to bring the SAM module in "Mute state" and after that to follow this order: switch-
off the Main Supply Voltage (+50V) and subsequently the Auxiliary Power Supply. (±24V).

System Description & Operating Rules

SAM351 is a BASH® 5.1 amplifier ( 6 x 100W) implementation utilizing the STA575 Integrated Circuit.

Specifically designed for multi-channel implementation in DVD - HTIB systems, Multi-Media systems, AV Re-
ceivers.
SAM351 is dimensioned to provide the maximum Output Power (THD=10 %) on two channels and instanta-
neously and 1/3 max Pout on the remaining Outputs, or 1/8 of max Pout continuous; this rule is important to
define the main Power Supply size (+50V).

Buck Regulator Description

The function of the buck regulator is to convert efficiently an input voltage to a lower voltage by adjusting the
ratio of the switching transistor's on-time to off-time. The resulting waveform is averaged by the output filter to
recover an analog signal.

In the BASH amplifier this output is in effect split in half by centering it on the audio ground to provide CD+ and
CD- rails.

To avoid the need for a high side driver for the transistor switch in the buck regulator the buck circuit recom-
mended has the switch in the return path. Hence the gate drive circuit (part of the STPB01) is referenced to the
negative return of the main supply that provides power for the buck regulator.

STA575

2 x100Watts

STA575

2 x 100Watts

Buck

Regulator

+50VDC

6 Ohm Loads

Audio

Inputs

STABP01

Controller

Dynamic Power Supply

(CD+ & CD

Signal Power Supply

+/-24V DC / 50

Signal Power Supply

Lines of Controls

STA575

2 x 100Watts

Audio

Input

STA575

2 x100Watts

STA575

2 x 100Watts

Buck

Regulator

+50VDC

6 Ohm Loads

Audio

Inputs

STABP01

Controller

Dynamic Power Supply

(CD+ & CD

Signal Power Supply

+/-24V DC / 50

Signal Power Supply

Lines of Controls

STA575

2 x 100Watts

Audio

Input

15/20

STA575

Interfacing STA575 to STPB01 (Feedback circuit)

This circuit produces a control signal current that is fed back to the STPB01 digital controller. The network used
in this example compares the track signal (STA575 track out) to a fixed ratio of buck regulator's output (CD+)
using a transistor. This method is effective because the controller's reference is the negative of the main DC
supply, which is not referenced to audio ground.

The tracking signal is generated inside the STA575 (track out) by taking the absolute value of the pre-amp's
output. The outputs of each channel and of each STA575 are then tied together in a diode-oring arrangement.
This means that the highest of any given output is the output that determines the tracking signal.

The absolute value circuit inside the STA575 has gain. This makes it possible to use an RC network and a re-
sistor divider to create a phase shift in the tracking signal at higher frequencies. This is also useful in optimizing
the alignment of the buck regulator's output with the output signal of the bridge amplifier at high frequency

This circuit first converts the buck switch current to a peak voltage. The control current is then converted to a
voltage (using a resistor) and added to the peak voltage. By doing this, the buck is better able to maintain the
desired headroom over a wide load range and output level.

Centering Network for CD+ & CD- Rails

The power rail of a bridge amplifier has no current flowing through the ground node, as the load is not connected
to ground. However there are several different small sources of dynamic and continuos ground currents flowing
from either CD+ or CD- to support the function of various things such as the control signal to the STABP01 con-
troller.

The centering network prevents these currents from shifting the CD+/- rails away from center i.e. away from a
symmetric split of the buck's output about ground. This is critical, even a small centering error requires an in-
crease in headroom which results in a significant drop in output losses. In its simplest form the centering network
could be a resistor divider from CD+ to CD- with its center tied to ground.

As long as the impedance is low enough (for example 200 ohms) this will swamp the smaller offset currents. It
is helpful to put this kind of passive network on the board with the STA575 devices to help when testing this
board on its own.

Power Amplifier Heatsink requirements

The heatsink requirements are dependent on several design goals. However there are two common references:
Pink noise at 1/8 of full power, all channels loaded. This would approximate a system with all channels repro-
ducing music at full volume with clipping occurring only occasionally. The second would be full power at 1kHz
for 5 minutes after a one hour pre-soak at 1/8 power.

The worse of these two is the full power test. A conservative approach is to assume that the heatsink would
come to thermal equilibrium after 5 minutes. Thus the Rth of the heatsink can be determined by:

For example in the STA575 the Rth jc is 1°C / W. R case-to-heatsink with grease is about 0.5°C / W. The max-
imum operating junction temperature is 130°C, which for margin should be derated to 120°C

Buck Regulator Heatsink

The Buck regulator heatsink can be designed in a similar manner and does not change by varying power supply.
In general the efficiency will be in the order of 85%. The thermal impedances from the junction(s) to the heatsink
may be lower and the maximum operating temperature will be higher.

Usually either the sub or the remaining channels are tested at full power. The result is that usually the Buck
heatsink is about ¼ the size of the linear heatsink, but this can be strongly affected by the design.

th heatsink

jm ax

am b

----------------------------------

th j ca se

th c as e to heatsink

STA575

16/20

Figure 8. PCBs AND COMPONENTS LAYOUT

SAM261 Specification

Parameter

Rating

Notes

Output Power

100Watts @10% - 6

see graphs

THD + N

< 0.05% @ 40 Watts
< 0.05% @ 75 Watts

Measured @ 1KHZ

SNR

-104 dB (relative to full power)
-113 dB (A-weighted)

Sensitivity

1 .3VRMS

Amplifier

Crosstalk

-76dB (relative to10W)

1KHz 8 Ohms,

Main Power Supply Inputs

60Volts @ 4 Amps

Maximum Voltage is 60V
Minimum Voltage is 50V

Aux Power Supply Inputs

+ 24 Volts @ 100mA
-24 Volts @ 100mA

Vs supply

Input Board

1 .3VRMS

Suplied to facilitate testing

4 Pin Harness

Power Supply Connections

9 Pin Harness

Audio Connections

Channel 1 and 2

50 VDC

Input

+/-24 VDC

Input

Mute

Channel 3 and 4

Channel 5

Channel 6

17/20

STA575

Figure 9. THD +N FR Channel

Figure 10. THD + N Frequency

Figure 11. Residual Noise vs. Frequency

Figure 12. Frequency Response

Audio Precision

0.01

0.02

0.05

0.1

0.2

0.5

140

100

110

120

130

Audio Precision

0.01

0.02

0.05

0.1

0.2

0.5

140

100

110

120

130

Audio Precision

0.01

0.02

0.05

0.1

0.2

0.5

20k

100

200

500

10k

Audio Precision

0.01

0.02

0.05

0.1

0.2

0.5

20k

100

200

500

10k

Pout = 80W

Pout = 30W

Pout = 5W

Audio Precision

-160

-140

-120

-100

-80

-60

-40

-20

dBr

20k

100

200

500

10k

Audio Precision

-160

-140

-120

-100

-80

-60

-40

-20

dBr

20k

100

200

500

10k

Audio Precision

+40

+10

+12

+14

+16

+18

+20

+22

+24

+26

+28

+30

+32

+34

+36

+38

dBr

40k

100

200

500

10k

20k

Audio Precision

+40

+10

+12

+14

+16

+18

+20

+22

+24

+26

+28

+30

+32

+34

+36

+38

dBr

40k

100

200

500

10k

20k

STA575

18/20

Figure 13. APPICATION BLOCK DIAGRAM

MUTE CONTROL &

THRESHOLD
REFERENCE

MUTE-BUCK

MUTE

OUT1+

OUT1-

OUT2+

OUT2-

OUT3+

OUT3-

OUT4+

OUT4-

IN1

IN2

IN3

IN4

-V

MUTE

BUCK CONTROLLER

300W BUCK

-V

DC++

GATE-DRIVE

I-SENSE

PWM-SPLY

GATE-DRIVE

I-SENSE

1800pF

TRACK

PROT

CD-

CD+

CD-

CD+

CD-

CD+

TRACK

PROT

THRESH-REF

-V

RED

WHITE

RED

WHITE

GND

DC++

STA575

2 CHANNELS

STA575

2 CHANNELS

MUTE-LIN

OUT5+

OUT0-

OUT6+

OUT8-

IN5

IN6

CD-

CD+

TRACK

PROT

R77

R78

-V

STA575

2 CHANNELS

D02AU1454

19/20

STA575

OUTLINE AND

MECHANICAL DATA

DIM.

inch

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

4.45

4.50

4.65

0.175

0.177

0.183

1.80

1.90

2.00

0.070

0.074

0.079

1.40

0.055

0.75

0.90

1.05

0.029

0.035

0.041

0.37

0.39

0.42

0.014

0.015

0.016

F (1)

0.57

0.022

0.80

1.00

1.20

0.031

0.040

0.047

25.75

26.00

26.25

1.014

1.023

1.033

H (2)

28.90

29.23

29.30

1.139

1.150

1.153

17.00

0.669

12.80

0.503

0.80

0.031

L (2)

22.07

22.47

22.87

0.869

0.884

0.904

18.57

18.97

19.37

0.731

0.747

0.762

L2 (2)

15.50

15.70

15.90

0.610

0.618

0.626

7.70

7.85

7.95

0.303

0.309

0.313

0.197

3.5

0.138

3.70

4.00

4.30

0.145

0.157

0.169

3.60

4.00

4.40

0.142

0.157

0.173

2.20

0.086

0.079

1.70

0.067

0.5

0.02

0.3

0.12

1.25

0.049

0.50

0.019

5° (Typ.)

3° (Typ.)

20° (Typ.)

45° (Typ.)

(1): dam-bar protusion not included
(2): molding protusion included

Flexiwatt27 (vertical)

FLEX27ME

7139011

Pin 1

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted
by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject
to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not
authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.

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20/20

STA575

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: STA575

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: STA575