Download Implementation of Power Supply Volume Control

Application Report
SLEA038 – July 2004
Implementation of Power Supply Volume Control
Tomas Bruunshuus
Texas Instruments Copenhagen
ABSTRACT
This document gives design guide lines for applications using the power supply volume
control (PSVC). The power supply volume control increases system performance by:
•
Volume can be decreased without loss of audio resolution, in the range where PSVC is
active.
•
When supply voltage for PVDD is decreased, the noise voltage at the output decreases as
well. The ratio between noise voltage and maximum RMS voltage (DNR) then increases.
The user experiences better noise performance at usual listening levels. E.g. a system
having 102 dB in DNR and a power supply range of 18 dB will have a SNR up to 120 dB.
•
Reduces power consumption and heat in the system at usual listening levels, thereby
increasing the lifetime of the system.
•
Many EMI tests are performed at a reduced volume setting. FTC requires 1/8 of maximum
output power equal to a volume setting of -9 dBFS. By use of the PSVC operating voltage
during EMI, the test will be reduced giving reduced switching noise in the system.
The PSVC is supported in Texas Instruments PWM processors like the TAS5508, which
makes implementation easy. For other modulator types like the TAS5066 and TAS5076,
the PSVC can also be implemented. However, on these devices all calculations and
control must be handled by the micro controller.
This document gives design guidelines, how to implement PSVC correctly for the
TAS5508. To implement PSVC for other PWM processors like the TAS5066 and
TAS5076, contact the Texas Instruments digital audio applications team.
1
SLEA038
Contents
1
Introduction .....................................................................................................................................3
1.1 PSVC Advantages.....................................................................................................................3
1.2 PSVC Concept ..........................................................................................................................3
2
General Structure............................................................................................................................5
2.1 Examples of Gain Settings ........................................................................................................7
2.1.1 Gain Setting Within the PSU Range..............................................................................7
2.1.2 Gain Setting Higher Than the PSU Range ....................................................................7
2.1.3 Gain Setting Lower Than the PSU Range.....................................................................7
2.2 Power Supply Control................................................................................................................8
2.3 TAS5508 PSVC PWM Output ...................................................................................................9
2.4 Programming the TAS5508 for PSVC.....................................................................................10
3
Power Supply Implementation.....................................................................................................12
3.1 TAS5508 0% Duty Cycle Handling..........................................................................................12
3.2 Power Supply Sink / Source....................................................................................................13
4
DC/DC Converter Application Example ......................................................................................15
4.1 Implementation........................................................................................................................15
References.............................................................................................................................................16
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figures
Digital and Power Supply Gain .........................................................................................4
Resulting Gain ....................................................................................................................4
Volume Calculation Flow Chart ........................................................................................6
Control of the Power Supply .............................................................................................8
PSVC PWM Pulse ...............................................................................................................9
Configuration Using PWM .................................................................................................9
PSVC Output of the TAS5508..........................................................................................10
PSVC With Saturation ......................................................................................................12
PSVC With Shutdown ......................................................................................................13
Basic Schematic for a Buck Converter ..........................................................................13
Buck Converter Using Synchronous Rectification .......................................................14
Use of a Bleeder Resistor to Sink Current.....................................................................14
Table 1.
Table 2.
Table 3.
Tables
System Control Register 1 (0x03) ...................................................................................10
PSVC Range Register (0xDF) ..........................................................................................11
General Control Register (0xE0) .....................................................................................11
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Implementation of Power Supply Volume Control
SLEA038
1
Introduction
1.1
PSVC Advantages
Using a combination of digital gain and power supply to the control volume setting gives several
advantages:
•
Volume can be decreased without loss of audio resolution, in the range where PSVC is
active.
•
When supply voltage for PVDD is decreased, the noise voltage at the output decreases as
well. The ratio between noise voltage and maximum RMS voltage (DNR) then increases.
The user experiences better noises performance at usual listening levels. E.g. a system
having 102 dB in DNR and a power supply range of 18 dB will have an SNR up to 120 dB.
•
Reduces power consumption and heat in the system at usual listening levels. Thereby
increasing lifetime of the system.
•
Many EMI tests are performed at reduced volume setting. FTC requires 1/8 of maximum
output power equal to a volume setting of -9 dBFS. By use of PSVC, the operating voltage
during EMI test will be reduced, giving reduced switching noise in the system.
With only a minimum extra complexity audio performance can be improved and EMI tests
become easier to pass.
1.2
PSVC Concept
Speaker output voltage can at be calculated as:
VSPEAKER (t ) = d (t ) ⋅ VPSU
Where d is the duty cycle that varies according to the audio signal and VPSU is the power supply
voltage. From this equation it can be seen that the output volume can be controlled from either
the duty cycle or the power supply voltage. Note that when the output volume level is calculated
in dB, the following formula is used:
VSPEAKER (dB) = d (dB ) + VPSU (dB)
Using this formula it becomes easier to calculate total output volume. The concept pf PSVC is to
have the power supply to control from 0 dBFS to e.g. -24 dBFS and then use digital gain to
control volume above 0 dBFS and below -24 dBFS. The lower crossover point (e.g. -24 dBFS)
can be selected differently depending on the power supply configuration.
Implementation of Power Supply Volume Control
3
SLEA038
Digital & Power Supply Gain (dB)
Power Supply Volume Control
30
20
10
0
-10
-20
-30
-40
-50
-60
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
Gain (dB)
Digital Gain
Figure 1.
Power Supply Gain
Digital and Power Supply Gain
Figure 1 shows gain settings for both digital circuits and a power supply at different desired
gains. The resulting gain (or volume level) is the two gains, digital and power supply gain, added
together. This is shown in Figure 2 according to the previous formula.
Power Supply Volume Control
60
Resulting Gain (dB)
40
20
0
-20
-40
-60
-80
-100
-80
-60
-40
-20
0
20
40
60
Desired Gain (dB)
Digital Gain
Figure 2.
Power Supply Gain
Digital Gain
Resulting Gain
The resulting gain is linear to the desired gain, where the power supply controls the gain from
-24 dBFS to 0 dBFS.
4
Implementation of Power Supply Volume Control
SLEA038
Note that minimum power supply gain (lower crossover point of -24 dBFS) must be selected
different depending on the power supply capability, e.g. -18 dBFS or -12 dBFS.
2
General Structure
To set the volume correctly, the volume setting must be split into a digital gain setting and a
power supply gain setting. Care must be taken to get these calculations right. Especially the
calculations at the two crossover points can cause non linear volume control if not done
correctly. The TAS5508 automatically calculates settings for digital gain and power supply gain.
A flow chart to calculate volume settings is shown in Figure 3. The principle is to set the power
supply volume according to the channel having the highest volume setting and then recalculate
gain setting for the digital circuits. The TAS5508 uses a sequence based on this flow chart to
calculate gain settings for digital gain and power supply gain.
Implementation of Power Supply Volume Control
5
SLEA038
Channel1_volume
Channel2_volume
.
.
Channel n_volume
Find Channel with highest
volume setting - channel_x
Calculate PSU setting for
channel_x
Higher
Is PSU setting
within PSU range
Lower
Within
range
PSU_volume = 0 dB
PSU_volume = min. dB
Calculate digital gain as:
Channel1_digital = Channel1_volume - PSU_volume
Channel2_digital = Channel2_volume - PSU_volume
.
.
Channel n_digital = Channel n_volume - PSU_volume
Figure 3.
6
Volume Calculation Flow Chart
Implementation of Power Supply Volume Control
SLEA038
2.1
Examples of Gain Settings
The following examples are for a three channel system. The power supply can be controlled
from -18 dB to 0 dB.
2.1.1 Gain Setting Within the PSU Range
System requirement settings:
Channel1_volume = -14 dB
Channel2_volume = -28 dB
Channel3_volume = -22 dB
Channel 1 is found to have the highest volume setting of -14 dB. The PSU_volume is then set to
-14 dB.
Digital gain is then calculated as:
Channel1_digital = -14 dB – (-)14 dB = 0 dB
Channel2_digital = -28 dB – (-)14 dB = -14 dB
Channel3_digital = -22 dB – (-)14 dB = -8 dB
2.1.2 Gain Setting Higher Than the PSU Range
System requirement settings:
Channel1_volume = -14 dB
Channel2_volume = 4 dB
Channel3_volume = -22 dB
Channel 2 is found to have the highest volume setting of +4 dB. The PSU_volume is then set to
0 dB, which is highest setting for the power supply.
Digital gain is then calculated as:
Channel1_digital = -14 dB – 0 dB = -14 dB
Channel2_digital = 4 dB – 0 dB = 4 dB
Channel3_digital = -22 dB – 0 dB = -22 dB
2.1.3 Gain Setting Lower Than the PSU Range
System requirement settings:
Channel1_volume = -28 dB
Channel2_volume = -28 dB
Implementation of Power Supply Volume Control
7
SLEA038
Channel3_volume = -22 dB
Channel 3 is found to have the highest volume setting -22 dB. The PSU_volume is then set to
-18 dB, which is lowest setting for the power supply.
Digital gain is then calculated as:
Channel1_digital = -28 dB – (-)18 dB = -10 dB
Channel2_digital = -28 dB – (-)18 dB = -10 dB
Channel3_digital = -22 dB – (-)18 dB = -4 dB
2.2
Power Supply Control
The output voltage of the power supply PVDD is controlled by adjusting the reference voltage.
The control loop in the power supply uses this reference voltage to regulate the output. When
the reference voltage is changed, PVDD will change accordingly.
PVDD
Feed Back
SMPS
-1
DC
reference
Figure 4.
Control of the Power Supply
The reference voltage must be controlled from the TAS5508. If the reference voltage is an
analog voltage that has to pass from the TAS5508 at the amplifier board to the power supply
board, the output voltage of the power supply will be erroneous. The voltage may drop when
crossing from one board to the next. This makes the volume setting inaccurate. Also, if noise or
hum is injected into the reference voltage, this noise will be coupled into the power supply output
and then into the speaker output.
This is solved in the TAS5508 by using a PWM signal instead of an analog reference voltage.
8
Implementation of Power Supply Volume Control
SLEA038
Lowest Power Supply
Voltage Pulse
Maximum Power Supply
Voltage Pulse
Figure 5.
PSVC PWM Pulse
The PSVC PWM pulse has a duty cycle corresponding to the power supply volume setting. The
advantage is that all volume information is independent of the voltage level. This means that any
voltage drop can be compensated by reclocking the PWM signal at the power supply board.
PWM pulses are then converted to the analog reference voltage through a low-pass filter.
PVDD
Feed Back
SMPS
-1
Reference
100 nF
Figure 6.
1 kΩ
10 kΩ
PSVC PWM
1 uF
74LVC126
Configuration Using PWM
The PSVC PWM frequency must be above 20 kHz to insure that no audible leftovers from PSVC
PWM are coupled into the speaker outputs.
2.3
TAS5508 PSVC PWM Output
When PSVC is enabled, the TAS5508 generates a PWM signal at a frequency of 44.1 kHz or
48 kHz. The PWM frequency is synchronized to the LRCLK of the I2S.
Implementation of Power Supply Volume Control
9
SLEA038
Lowest Power Supply
voltage Pulse > 120 out of
2048
Maximum Power Supply
Voltage
Pulse =
1944 out of 2048
Figure 7.
PSVC Output of the TAS5508
The output has a maximum duty cycle of 95% corresponding to 0 dBFS and a minimum duty
cycle of 6% corresponding to -24-dB attenuation.
Note that during start up, error recovery, and reset the duty cycle is 0%, 0 V. This can be
changed by programming system control register 1 (0x03).
Table 1.
D7
System Control Register 1 (0x03)
D6
D5
D4
D3
D2
D1
D0
-
-
-
-
-
-
-
PWM High Pass Disabled
1
-
-
-
-
-
-
-
PWM High Pass Enabled
-
0
-
-
-
-
-
-
/Auto Clock Set
-
1
-
-
-
-
-
-
Manual Clock Set
-
-
-
0
-
-
-
Soft Unmute on Recovery from Clock Error
0
Function
-
-
-
1
-
-
-
Hard Unmute on Recovery from Clock Error
-
-
-
-
1
-
-
-
PSVC Hi-Z Enable
-
-
-
-
0
-
-
-
PSVC Hi-Z Disable
0
0
0
1
0
0
0
0
Default Setting
D0 to D2 is unused bits.
If D3 bit is set high, the PSVC output will go into Hi-Z during error recovery. This is however not
recommended, since this interferes with the reclocking gate at the power supply board, causing
PVDD voltage to be too high. For most applications, PSVC Hi-Z must remain disabled.
The function of D4 to D7 is not covered in this document, see Reference 1.
2.4
Programming the TAS5508 for PSVC
The TAS5508 modulator has a PWM output for the power supply control. This provides an easy
implementation of the PSVC. The modulator does all calculations to get the correct volume
setting and generates the PSVC PWM pulse required at a frequency of 44.1 kHz or 48 kHz,
depending on the audio sample rate.
10
Implementation of Power Supply Volume Control
SLEA038
The TAS5508 can be configured to provide PSVC with 12.04-dB, 18.06-dB, or 24.08-dB
attenuation of the power supply. The attenuation level should be selected as high as possible.
The limiting factor is that the power supply must remain stable at all power levels. Some power
supplies can have difficulties when regulating over a wide voltage range. Hence, the PSVC
range must be selected smaller.
The PSVC control range is set in register 0xDF.
Table 2.
PSVC Range Register (0xDF)
D31 – D2
D1
D0
Function
0
0
0
0
12.04-dB control range for PSVC
0
0
0
1
18.06-dB control range for PSVC
0
0
1
0
24.08-dB control range for PSVC
0
0
1
1
Ignore – retain last value
0
0
1
0
Default Setting
Subwoofer configuration must be selected. In case that the subwoofer output is a line output, the
digital volume setting is not to be affected when setting the power supply volume.
This is done in register 0xE0. This register also enables/disables the PSVC.
Table 3.
D31 – D4
D3
General Control Register (0xE0)
D2
D1
-
0
/8 Channel Configuration
0
-
1
6 Channel configuration
0
0
-
Power Supply Volume Control Disable
0
1
-
Power Supply Volume Control Enable
0
D0
Function
0
0
-
-
Subwoofer Part of PSVC
0
1
-
-
Subwoofer Separate from PSVC
0
0
0
0
0
Default Setting
The D1 bit is used to select between eight channel configuration and six channel configuration.
This item is not covered in this document.
The D2 bit is used to enable/disable PSVC. Default is disabled. When PSVC is disabled, the
output of PSVC is 0. All volume control is performed using digital gain only. Enabling of the
PSVC starts the PSVC PWM. The TAS5508 automatically calculates the volume setting for the
power supply and digital volume for all channels based on the flow chart shown in Figure 3.
If D3 is set to 1, the subwoofer channel (channel 8) is not included in the PSVC, only digital
volume is used. This is needed if the subwoofer output is a line out (e.g. a 7.1 system using
active subwoofer).
Implementation of Power Supply Volume Control
11
SLEA038
3
Power Supply Implementation
3.1
TAS5508 0% Duty Cycle Handling
As discussed in the previous section, the TAS5508 during start up and error recovery has a
PSVC output of 0% duty cycle. The power supply must then be able to handle this situation
properly. When the reference voltage to the power supply is 0 V, PVDD will also be 0 V if no
special arrangements are made.
NOTE: Texas Instruments power stages can handle PVDD being 0 V, since no audio is present
during these events. Texas Instruments power stages does not need protection against PVDD =
0 V. However, the power supply must not be damaged nor become unregulated during these
events.
If the power supply cannot handle a 0-V output, the following arrangements can be made:
PVDD
Feed Back
SMPS
-1
Reference
100 nF
Figure 8.
1 kΩ
10 kΩ
PWM
ref
1 uF
74LVC126
PSVC With Saturation
Figure 8 shows a power supply implementation, where PVDD is kept at a minimum voltage
when PWM is 0%. The voltage is set by a resistor divider and the forward drop of the diode.
Another way of controlling 0% situation is to shut down the power supply when the duty cycle
falls below a given level. This is shown in Figure 9.
12
Implementation of Power Supply Volume Control
SLEA038
PVDD
Feed Back
SMPS
-1
Reference
10 kΩ
1 kΩ
1 uF
100 nF
PWM
ref
74LVC126
/shutdown
74LVC126
10 nF
Figure 9.
3.2
10 kΩ
PSVC With Shutdown
Power Supply Sink / Source
Most power supplies are only capable of sourcing current. This is due to implementation of the
rectifying circuit on output. In most cases, this is done by using a rectifying diode.
Figure 10 shows basic components for a buck converter. The buck converter creates an output
voltage (PVDD) lower than its input voltage (VI). It can be seen that current can only flow out of
the converter due to the direction of the diode and since the input voltage is higher than the
output voltage, no current can flow from the PVDD to VI. Decreasing of the output voltage can
only happen by loading the output.
Current
Source
VI
PVDD
Figure 10. Basic Schematic for a Buck Converter
Implementation of Power Supply Volume Control
13
SLEA038
When using PSVC, this can cause a problem when ramping down volume. When the volume is
ramped down, the PVDD voltage must decrease. If the power supply can only source current,
only the amplifier load can decrease the PVDD voltage. This causes an uncontrolled ramp down
of the volume.
To make the power supply able to sink current as well, one of following solutions is
recommended.
Use of synchronous rectification. The basic theory is to replace the rectifying diode with a
controlled MOSFET. A controlled MOSFET has the advantage to allow current in both directions
when turned on. Actual implementation of a synchronous rectification depends on the power
supply topology. Figure 11 shows an example of synchronous rectification for a buck converter.
Current Sink/Source
PVDD
VI
Figure 11. Buck Converter Using Synchronous Rectification
Use of bleeder resistor. A resistor can be placed at the PVDD output to bleed down the output
voltage. In order not to decrease efficiency, this resistor must be connected through a switch or
a transistor. The bleeder resistor will then only be active when needed.
Figure 12 shows how a controlled bleeder resistor can be used to decrease the output voltage.
The bleeder resistor is turned on by the switch when the PVDD voltage is too high.
Current
Source
VI
PVDD
Current
Sink
Figure 12. Use of a Bleeder Resistor to Sink Current
14
Implementation of Power Supply Volume Control
SLEA038
4
DC/DC Converter Application Example
The following application example is a dc/dc converter optimized for the full advantage of the
TAS5508. The converter is designed for:
4.1
•
Input voltage 50 V to 55 V
•
Output voltage 2 V to 40 V, giving the full 24.08-dB attenuation provided by the TAS5508
•
Current limitation level set to 12 A
Implementation
The power supply is designed with the possibility to use remote voltage sensing, which improves
audio performance, see Reference 2. The output voltage is sensed through a separate
connector J704 pin 2. The voltage can then be sensed at the amplifier board eliminating
impedances in wires and connectors.
For using the PSVC, a jumper must be placed at J703 between pin 1 and pin 2. If a manual
voltage setting is required, the jumper must be placed between pin 2 and pin 3.
The PWM input for power supply control from the TAS5508 is at J703 pin 5. The input has a
pulldown resistor, R827, to insure that the output voltage drops to 0 V in case of loss of PWM
input. To restore the PWM signal and adapt it to the power supply reference voltage, the PWM
input is reclocked in an AND-gate, U703. This removes voltage drops and noise that might have
been injected in the transmission from the modulator to the power supply. Converting the PWM
signal level to the power supply reference voltage improves the accuracy of the output voltage.
The converter itself is a BUCK topology. Basic components can be identified as: C708, C710,
C711, and C712 as the input capacitor, Q706 and Q707, L704 and C725 plus capacitors at the
amplifier board as the output capacitor. U706 is an integrated power supply controller.
Synchronous rectification is used in this application. Q707 is the synchronous rectifier instead of
a diode. The dc/dc converter is then capable of transferring current from output side to the input
side.
Since the dc/dc converter can be supplied from a rectified transformer output, there must be a
bleeder at the primary side, to be able to sink current. The bleeder resistor is R707 and is
controlled by Q701. Q701 is turned on by U701C, if the input voltage exceeds 65 V.
Implementation of Power Supply Volume Control
15
SLEA038
References
1. TAS5508 – 8 Channel Digital Audio PWM Processor (SLES091)
2. Power Supply Considerations for A/V Receivers (SLEA028)
16
Implementation of Power Supply Volume Control
4
3
No.: 49
PSU Input voltage filter
2
No.: 47
PSU Power stage
L701
1u
VIN
VIN
1 2 VIN-POS
J701
C707
10n
C706
100n
C711
1000u
C712
1000u
R713
20k
1
VIN-RTN
C704
10n
R714
10k
Q703
C718
2
R717
0
1
0
+
C780
47u
0
C782
100n
connector4
C722
100n
0
C724
10n
R726
R696
2R7
R727
2R7
2R7
R695
2R7
L704
57uH / T131-8/90
3
R697
20k
Q712 2
1
2
C728
NU
R728
R729
NU
0R018
C725
1000u
4
C727
10n
1
C726
100n
2
3
+12V
Q705
VIN-RTN
0
B
4
+5V
J706
connector4
-I-sense
2
0
R731
10R
+I-sense
R730
0R018
3
1
1
47k R719
47k
C723
10n
3
Q707
IRF540
R725
0R
220n
C721
0
R716
+5V
+
C783
47u
RUN
0
R724
HIP2100
C720
22p
connector4
J707
+VPWR
Q706
IRF540
3R3
U702
Vdd 1
HB 2
HO 3
HS 4
8 LO
7 Vss
6 LI
5 HI
R718
10k
100R
0
4
C719
22p
2
22p
R715
PSU-PWM
C781
100n
Q704 3
1
20k
0
2
3
C717
22p
R721
4k7
3
+12V
J705
B
75nH
+
L702
1u
R702
10R
R720
4k7
R722
20k
1 2VIN-NEG
C703
100n
L703
3R3
+
C710
1000u
+
C708
1000u
+
C705
1000u
+
+
C702
10n
R700
10R
0
J702
R723
+12V
R701
10R
C701
100n
1
0
0
0
0
0
No.: 48
PSU Input voltage bleeder
No.: 46
PSU Controler
3
1
BAV70
VIN
+12V
+V-sense
2
D708
R821 120k
R820
+5VREF
C745
R751
5k6
0
R752
5k6
100k
12
VIN-RTN
C715
47u
R709
100k
V+
C716
100n
+
LM339
Q701
IRF540
10 -
0
VIN-OV
13
U706
24 SHARE
12
0
PSU-PWM
0
0
0
+12V
R745
+5VREF
No.: 44
Temperature detector for PSU
R794
+12V
82k
R801
3k
A
R798
33k
R795
1
+12V
U701A
5 +
V+
V-
4 LM339
12
R797
100R
+12V
CA- 6
18 GND
CAO 7
17 OUT
CS+ 8
16 VCC
CS- 9
15 RUN
CSO 10
14 VREF
ENBL 11
13 KILL
SEQ 12
CAC749
22p
100R
R823
100R
R747
27k
R748
8k2
C750
4n7
0 0
R750 C755
82R
0
VOLUME
R757
C754
10u
0
0
R758
510R
CS+
+I-sense
CSR749
3k3
R760
5k6
C756
220p
0
R761
8k2
0
C758
220n
R759
510R
-I-sense
+5VREF
R762
1k5
0
A
C784
100n
0
R793
10k
3
1
TP-PSU
VOLUME
V12
TITLE
R825
2k
DC/DC converter
POT
R826
10k
2-40V max 12A
SIZE DWG NO
0
A3
SCALE NONE
3
Confidential
All rights belongs to
Texas Instruments
Inc.
Texas Instruments Denmark A/S
0
J703
0
4
100p
1k5
R756
27k
R763
C753
10u
0
C751
220p
R822
C752
100n
TBLK-A/B/C/G
Y 4
1
R800
30k
10k
VAO
+5VREF
3 GND
2
R802
33k NTC
0 4k7
3
C779
10n
19 VEE
1 2 3
6 LM339
0
2B
+5VREF
V+
1k
D705
BAV70
0
U703
5
1A
VCC
100n
R827
U701B
7 +
2
+VPWR
0
82k
0
C778
R796
R799
10k
VIN-OV
TW-PSU
2
0
R753
1k0
R746
270k
VA+ 4
VAO 5
C744
100n
0
C748
1n
J704
5_pol_pow
11
22
33
44
55
R824
R792
10k
3
1k
TP-PSU
0
C746
VA100p C747
22p
+V-sense
D710
+5VREF
5k6
C743
100n
No.: 45
Remote sense, voltage control
VA- 3
RT
7k5 20
CLKSYN
R744
510R
100n
ADJ 1
ILIM 2
R743 21
VU701D
LM339
UC3849DW
23 OSC
R742 100R22
RDEAD
+
V-
8 -
1nF
3
11 +
3
R708
10k
C741
0
+
C713
220p
R699
2k7
R712
10k
1
V+
R704
10k
C714
100n
14
R711
470k
2
+5VREF
1k8
2
3
R710
8k2
D701
BAV70
1
3
9 +
R707
82R
1
U701C
R706
2k7
R755
1k0
D704
BAV70
3
+12V
R705
220k
R703
120k
R754
2
RUN
R698
8k2
VIN
2
A706-SCH-001
2004-05-23
1
SHEET
REV
1.0
1 OF 1
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