Maxim > Design=20 support > App = notes=20 > Amplifier=20 and Comparator Circuits > APP = 4943
Maxim > Design = support >=20 App = notes=20 > Audio=20 Circuits > APP 4943
Maxim > Design = support >=20 App = notes=20 > Automotive=20 > APP 4943

Mar 31, = 2011

Keywords: MAX13300, MAX13301, Class D, = Class D=20 audio, high power audio, automotive audio, automotive = Class D,=20 automotive Class D audio
Related=20 parts

Download,=20 PDF format (204kB)

[?]

APPLICATION NOTE 4943

Diagnosing Automotive Faults with Class D = Audio=20 Amplifiers

By:	Jon=20 Wallace

Abstract: This=20 application note explains how to run the diagnostics = for the=20 MAX13300/MAX13301/MAX13302 automotive Class-D = amplifiers.=20

Attend=20 this brief webcast by Maxim on=20 = TechOnline

Introduction

The MAX13300 = automotive Class=20 D audio amplifiers incorporate many built-in = diagnostics=20 to help locate faults in the system. The amplifiers = detect the=20 following fault conditions on the speaker outputs when = there=20 is no audio present. Since audio may not be present = during=20 these tests, those tests are typically run once at = startup or=20 only when requested in factory diagnostic mode.=20

Short to ground=20
Short to battery=20
Open load=20
Resistance measurement=20
Tweeter present=20
Output offset

There is another set of=20 diagnostics designed to run continuously while audio = is=20 present. These diagnostics give the system feedback on = the=20 state of the MAX13300/MAX13301/MAX13302.=20

Clipping detection=20
Thermal warning detection=20
Charge pump undervoltage=20
Supply undervoltage=20
Supply overvoltage

Startup Procedure

To avoid unwanted click-and-pop=20 at startup, use the following procedure (Figure = 1):=20

Set the state of active-low MUTE_CL1 to select = the LSB=20 of the I=C2=B2C address.=20
Pull the EN pin high.=20
Release active-low MUTE_CL1.=20
If more than two I=C2=B2C address's are needed, = first write=20 to CTRL4.ADR[1:0] to set the new address and then = write=20 CTRL5.ADRDF =3D 0 to enable a new address.=20
Increase the short-circuit current=20 threshold by setting CTRL1.CLTH =3D 0. This = guarantees that=20 there is no false trigger of the short-circuit = diagnostic=20 because of a current imbalance at startup.=20
Enable the device by setting CTRL2.STBY =3D 0.=20
Enable a precharge of inputs by setting = CTRL1.PRE =3D 1.=20
Set CTRL2.MD01 =3D 10 and CTRL2.MD23 =3D 10. = This will=20 precharge the output capacitors to PVDD/2.=20
Set CTRL0, CTRL1.CLVL[1:0], CTRL1.MD[1:0], = CTRL3.HCL,=20 CTRL3.LDM, CTRL4, and CTRL5 to desired values based = on=20 application requirements.=20
Wait at least 10ms from step 7. Disable the = precharge=20 circuit by setting CTRL1.PRE =3D 0.=20
Wait 100ms =C3=97 C_DCB (=C2=B5F) for = the input bias voltage=20 to stabilize. This means that if you are using a = 2.2=C2=B5F=20 DC-blocking capacitor on the inputs, then wait at = least=20 220ms. Decreasing this time will increase the = click-and-pop=20 noise generated at startup.=20
Optional: set CTRL2.MD23[1:0] =3D = CTRL2.MD01[1:0] =3D 01 and=20 delay at least 50ms before proceeding. This sets the = outputs=20 to MUTE mode.=20
Set CTRL2.MD23[1:0] =3D CTRL2.MD01[1:0] =3D 11. = This sets=20 the outputs to PLAY mode.=20
Set the short-circuit diagnostic threshold back = to=20 normal by setting CTRL1.CLTH =3D 1.

ADRDF	ADR1	ADR0	Active-Low MUTE_CL1	I=C2=B2C ADDR (WR)	I=C2=B2C ADDR (RD)
0	0	0	=E2=80=94	0xD8	0xD9
0	0	0	=E2=80=94	0xDA	0xDB
0	1	1	=E2=80=94	0xDC	0xDD
0	1	1	=E2=80=94	0xDE	0xDF
1	=E2=80=94	=E2=80=94	0	0xD8	0xD9
1	=E2=80=94	=E2=80=94	1	0xDA	0xDB

Figure=20 1. Startup procedure.

Three-State Procedure

To avoid unwanted = click-and-pop=20 at shutdown, use the following procedure (Figure = 2):=20

If the audio source=20 is already muted, then go to step 4.=20
Set the outputs to mute mode by setting = CTRL2.MD23[1:0]=20 =3D CTRL2.MD01[1:0] =3D 01.=20
Wait at least 50ms to ensure no click-and-pop = from a=20 20Hz signal.=20
Three-state the outputs by setting = CTRL2.MD23[1:0] =3D=20 CTRL2.MD01[1:0] =3D 00.

Figure=20 2. Three-State procedure.

Shutdown Procedure

To avoid unwanted = click-and-pop at=20 shutdown, use the following procedure (Figure = 3):=20

Three-state the outputs by following the = three-state=20 procedure outlined above.=20
Enter standby mode by setting CTRL2.STBY =3D 1.=20
Pull the EN pin low.

Figure=20 3. Shutdown procedure.

Load Diagnostics

Short-to-Battery Diagnostic Procedure

This = diagnostic=20 detects a short to battery or ground of less than = 1k=CE=A9 on any=20 output. The diagnostic for short to battery and ground = is done=20 at the same time and in the same diagnostic mode, = however, the=20 device must be out of standby mode to run the = short-to-ground=20 diagnostics. None of the results are latched, so the = OSTAT2=20 register must be read while running this diagnostic to = obtain=20 a valid status.

If the load is present, a short = on=20 either of the differential=20 outputs results in a short on the other output. = Therefore, the=20 OSTAT2 status register only indicates which channel's = output=20 is shorted and not which of its differential outputs = is=20 shorted. The I=C2=B2C status register can indicate, = for example,=20 that output 1 is shorted to battery; it cannot = differentiate=20 between an OUT1+ and OUT1- short to battery.

To = determine if a short to ground or battery exists on = any of the=20 outputs, three-state all outputs through I=C2=B2C and = enter standby=20 (CTRL2.STBY =3D 1). Run the short-to-ground/battery = diagnostic=20 by setting the CTRL3.SDET (short-to-ground/battery = diagnostic=20 enable) bit to 1. The results of the diagnostic are = reported=20 in the OSTAT2.SBAT[3:0] (short-to-battery indicator) = bits.=20 Ignore all other fault indications as they are not=20 valid.

Because no latch is set, a short to = ground or=20 battery does not prevent the device from powering up.=20 Therefore, the microcontroller can enable the device = into a=20 short, although this configuration is discouraged. = Should the=20 device be enabled into a short, the real-time = overcurrent will=20 latch the shorted channel off. The MAX13300/MAX13301 = offer=20 real-time protection for short to battery, short to = ground,=20 and shorted load to prevent damage to the = device.

Step-by-Step Procedure (Figure 4)

The device must be in standby mode to complete = this=20 diagnostic. If starting from MUTE or PLAY mode, = follow the=20 normal shutdown procedure to prevent click-and-pop.=20
Enable the short-to-battery diagnostic by = setting=20 CTRL3.SDET =3D 1.=20
Wait a minimum of 200=C2=B5s.=20
Read the OSTAT2.SBAT[3:0] bits for results.=20
Disable the short-to-battery diagnostic by = setting=20 CTRL3.SDET =3D 0.

Figure=20 4. Short-to-V_BAT diagnostic = procedure.

Short-to-Ground Diagnostic Procedure

This = diagnostic=20 detects a short to ground of less than 1k=CE=A9 on any = output. The=20 diagnostic for short to battery and ground is done at = the same=20 time and in the same diagnostic mode. None of the = results are=20 latched, so the OSTAT2 register must be read while = running=20 this diagnostic to obtain a valid status.

If = the load=20 is present, a short on either of the differential = outputs=20 results in a short on the other output. Therefore, the = status=20 register only indicates which channel's output is = shorted and=20 not which of its differential outputs is shorted. The = I=C2=B2C=20 status register can indicate, for example, that output = 1 is=20 shorted to battery, but it cannot differentiate = between an=20 OUT1+ and OUT1- short to battery.

To determine = if a=20 short to ground or battery exists on any of the = outputs,=20 three-state all outputs through I=C2=B2C. Run the=20 short-to-ground/battery diagnostic by setting the = CTRL3.SDET=20 (short-to-ground/battery diagnostic enable) bit to 1. = During=20 the diagnostic, the device shunts a 3k=CE=A9 resistor = across each=20 differential output to ground and sources 2mA of = current to=20 each output from PVDD. Under normal conditions, 6V is=20 developed at each output. An output voltage > 6V is = interpreted as a short to battery. An output voltage = < 6V=20 is interpreted as a short to ground. Results of the = diagnostic=20 are reported in the OSTAT2.SBAT[3:0] (short-to-battery = indicator) and OSTAT2.SGND[3:0] (short to ground)=20 bits.

Because no latch is set, a short to = ground or=20 battery does not prevent the device from powering up.=20 Therefore, the microcontroller can enable the device = into a=20 short, although this configuration is discouraged. = Should the=20 device be enabled into a short, the real-time = overcurrent will=20 latch the shorted channel off. The MAX13300/MAX13301 = offer=20 real-time protection for short to battery, short to = ground,=20 and shorted load to prevent damage to the = device.

Step-by-Step Procedure (Figure 5)

The outputs must be in three-state mode with the = charge=20 pump active (CTRL2.STBY =3D 0). If starting from = MUTE or=20 PLAY mode, follow the normal shutdown procedure to = prevent=20 click-and-pop.=20
Enable the short-to-ground diagnostic by setting = CTRL3.SDET =3D 1.=20
Wait a minimum of 200=C2=B5s.=20
Read the OSTAT2.SGND[3:0] bits for results.=20
Disable short-to-ground diagnostics by setting=20 CTRL3.SDET =3D 0.

Figure=20 5. Short-to-ground diagnostic procedure.

Open Load Detection

This diagnostic detects an = open=20 between OUT_+ and OUT_- of > 70=CE=A9 or > = 200=CE=A9, depending on=20 the value of the CTRL.LDM (load detect threshold)=20 bit.

To detect open loads, three-state the = outputs=20 through I=C2=B2C and discharge the output capacitors = by setting the=20 CTRL3.DIS (discharge) bit to 1. Run the open-load = diagnostic=20 test by setting CTRL3.RDET (open-load diagnostic = enable) to 1.=20 During the diagnostic, all low-side=20 FETs on negative outputs (OUT_-) are turned on while = all other=20 FETs are turned off. The device sources a 2mA current = from=20 OUT_+ to OUT_-. If a load is not present, OUT_+ swings = high=20 and its relatively high VOUT_+ is interpreted as an = open=20 output. Results of the diagnostic are reported in the=20 OSTAT0./LDOK[3:0] (load OK indicator) bits.

Step-by-Step Procedure (Figure 6)

The outputs must be in three-state mode with the = charge=20 pump active (CTRL2.STBY =3D 0). If starting from = MUTE or PLAY=20 mode, follow the normal shutdown procedure to = prevent=20 click-and-pop.=20
Set CTRL3.LDM based on application requirements. =
Discharge the outputs to ground by setting = CTRL3.DIS =3D 1=20 to prevent click-and-pop during diagnostics.=20
Wait at least 200=C2=B5s.=20
Enable the open-load diagnostic by setting = CTRL3.RDET =3D=20 1 and CTRL3.DIS =3D 0.=20
Wait at least 200=C2=B5s.=20
Read OSTAT0.OC[3] bits. If any of the = OSTAT0.OC[3:0]=20 bits are low, the OSTAT1.LDOK[3:0] bits are not = valid due to=20 a short to V_BAT on the channel(s) = indicated by=20 the OSTAT0.OC[3:0] bits. Therefore, go to step 9.=20
Read OSTAT1.LDOK[3:0] for results.=20
Disable the open-load diagnostic by setting = CTRL3.RDET =3D=20 0.

Figure=20 6. Open-load diagnostic procedure.

Shorted Load/Resistance Measurement = Detection

This=20 diagnostic can measure the resistance=20 of the load so that shorted loads on any of the = outputs can be=20 detected. Since a resistance can be calculated from = the=20 diagnostic, this diagnostic can also be used as an = alternate=20 method to detect open load or to determine if the = speaker is=20 present. To detect shorted loads, place the device in = normal=20 mode; set the CTRL3.TW (tweeter/shorted load = diagnostic=20 select) bit to 0; set MAP.LCTM=20 to 1 to map the active-low LOAD_ fault bits to the = active-low=20 CL0 pin; and apply a =E2=89=A4 20Hz sinusoidal signal = or single=20 half-sine signal pulse to the inputs under test. The = amplitude=20 of the signal will depend on application requirements. = The=20 device compares the load current to the shorted = load-current=20 threshold. If the load current exceeds the threshold, = the=20 corresponding STAT3./LOAD_ (load indicator) bit is set = to 1,=20 indicating that there is a shorted load. The shorted=20 load-current threshold depends on the programmed = current=20 limit. (See the Electrical Characteristics table in = the data=20 sheet.) A similar procedure can be used to detect an = open load=20 by using a larger amplitude sinusoidal = signal.

Note=20 that the active-low LOAD_ bits do not latch high upon=20 detecting a short. During zero crossings, the load = current=20 does not exceed the threshold and the active-low LOAD = bits are=20 cleared to 0. There are two ways to obtain the results = of the=20 shorted-load diagnostic:=20

Continuously read the active-low LOAD_ bits to = determine=20 if any have been set high.=20
Monitor the open-drain=20 active-low CL0 output. Because active-low CL0 is the = NORed=20 function of the active-low LOAD bits, active-low CL0 = pulls=20 low if a short exists on any of the outputs. =

Mask=20 the active-low LOAD_ bits to the active-low CL0 output = by=20 setting the MAP.LCTM (tweeter and shorted load mask) = bit to 0=20 when the shorted-load diagnostic is not longer = running.=20 Clearing this bit prevents active-low CL0 from being = asserted=20 when the shorted load-current threshold is exceeded = during=20 play.

A load-resistance-measurement diagnostic = is done=20 on all outputs. A shorted load is traceable to the = output on=20 which it exists by examining the active-low LOAD_ bits = or=20 injecting the sinusoidal signal into one channel at a = time.=20

Step-by-Step Procedure (Figure 7)

Enter PLAY mode by following the normal startup=20 procedure.=20
Select the low-current threshold by setting = CTRL3.HCL =3D=20 0. This current is approximately 1.3A. (See the = Electrical=20 Characteristics table in the data sheet.)=20
Map the diagnostic current threshold to the = active-low=20 CL0 pin by setting MAP.LCTM =3D 1.=20
Set the current threshold to a high setting for = short=20 detection by setting CTRL3.TW =3D 0. If you are = running an=20 open test, set CTRL3.TW =3D 1 to select the lower = current=20 threshold setting.=20
For each output [0 to 3]:=20
- Generate a low-frequency sine wave (typically = =E2=89=A4 20Hz)=20 or single-pulse half-sine wave with the amplitude = based on=20 application requirements. If the amplitude of the = sine=20 wave is ramped until active-low CL0 is active, = then the=20 exact speaker impedance can be measured.=20
- Monitor active-low CL0 or read = OSTAT1.LOAD[3:0] to=20 determine whether the current threshold is = crossed. This=20 status is not latched, so it will toggle on/off = based on=20 the signal amplitude. If monitoring active-low = CL0, you=20 must apply the input signal to one channel at a = time. You=20 can also read the active-low LOAD status bits = through the=20 I=C2=B2C to determine which output caused the = active-low CL0=20 pin to assert.
Remove the diagnostic current threshold mapping = by=20 setting MAP.LCTM =3D 0.

There are several = ways to=20 measure the exact resistance of the load:=20

Ramp up the sine wave or half-sine pulses slowly = until=20 the active-low CL0 pin is asserted for the first = time. The=20 resistance is then calculated by:=20
=20
Where:
I_T =3D Threshold = current set=20 by CTRL3.HCL
V_INP =3D Peak input = voltage=20 signal
GAIN =3D Gain=20 setting of the channel
Use a sine wave or a single half-sine pulse with = an=20 amplitude guaranteed to trip the selected threshold = current=20 with expected load resistance. When the test signal = is=20 applied, measure the amount of time that active-low = CL0 is=20 low. From this the load resistance can be calculated = as=20 follows:=20

=
=20

Figure=20 7. Shorted-load diagnostic procedure.

Tweeter Detection

This diagnostic detects = whether a=20 tweeter is properly connected when a passive crossover=20 is used. To detect shorted loads, place the device in = normal=20 mode; set the CTRL3.TW (tweeter/shorted load = diagnostic=20 select) bit to 1; set MAP.LCTM to 1; and apply a 15kHz = to 25Hz=20 sinusoidal signal to all the inputs. The device = compares the=20 load current to the tweeter-detect current threshold. = If the=20 load current exceeds the threshold, the corresponding=20 STAT3./LOAD_ (load indicator) bit is set to 1, = indicating that=20 there is a tweeter. The amplitude of the input signal = depends=20 on the impedance versus frequency characteristics of = the=20 tweeter. Correct tweeter detection requires that the = amplitude=20 be large enough to trip the threshold when a tweeter = is=20 present.

Note that the active-low LOAD_ bits do = not=20 latch high upon detecting a tweeter. During zero = crossings,=20 the load current does not exceed the threshold and the = active-low LOAD_ bits are cleared to 0. There are two = ways to=20 obtain the results of the tweeter detection = diagnostic:=20

Continuously read the active-low LOAD_ bits to = determine=20 if any have been set high.=20
Monitor the open-drain active-low CL0 output. = Because=20 active-low CLP0 is the NORed function of the = active-low=20 LOAD_ bits, active-low CLP0 pulls low if a short = exists on=20 any of the outputs.

Mask the active-low = LOAD_ bits=20 to the active-low CL0 output by setting the MAP.LCTM = (tweeter=20 and shorted load mask) bit to 1 when the tweeter = detection=20 diagnostic is no longer running. Doing this prevents=20 active-low CL0 from being asserted when the = tweeter-detect=20 current threshold is breached during play.

The = tweeter=20 detection diagnostic is done on all outputs. The = presence of a=20 tweeter is traceable to any output by examining the = active-low=20 LOAD_ bits. The presence of a tweeter on output 3 = causes=20 active-low LOAD3 to go high, etc.

Step-by-Step Procedure (Figure 9)

Set CTRL3.HCL =3D 0.=20
Map the diagnostic current threshold to the = active-low=20 CL0 pin by setting MAP.LCTM =3D 1.=20
Enter PLAY mode by following the normal startup=20 procedure.=20
Set the diagnostic current threshold to low by = setting=20 CTRL3.TW =3D 1.=20
For each output [0 to 3]:=20
- Generate a high-frequency sine wave (15kHz to = 25kHz)=20 with an amplitude based on application = requirements. You=20 must check one output at a time to determine which = output=20 has an open tweeter.=20
- Monitor active-low CL0 or read = OSTAT1.LOAD[3:0] to=20 determine whether the current threshold is = crossed. This=20 status is not latched, so it will toggle on/off = based on=20 the signal amplitude.
Remove the diagnostic current-threshold mapping = by=20 setting MAP.LCTM =3D 0.=20
Select the normal diagnostic current threshold = by=20 setting CTRL3.TW =3D 0.

To select the = optimum=20 input-voltage amplitude, measure the speaker impedance = with=20 and without a tweeter present at the test frequency = selected.=20 Below is a typical 4=CE=A9 speaker impedance curve = with and without=20 the tweeter present.

Figure=20 8. Typical 4=CE=A9 speaker impedance vs. = frequency.

With=20 a test frequency of 20kHz the optimum input voltage is = where=20 the active-low CL0 pin asserts with a speaker = impedance of:=20

=20

Where:
R_TW =3D Speaker = impedance with=20 tweeter presen
R_NO-TW =3D Speaker = impedance with=20 no tweeter

Using the equation above and the = data in=20 Figure 8:=20

=20

Figure=20 9. Tweeter diagnostic procedure.

Continuous Diagnostics

The = MAX13300/MAX13301/MAX13302=20 constantly monitor critical performance and safety = parameters=20 such as output offset voltages, output clipping, = thermal=20 faults, and under- and overvoltage conditions. The = results are=20 reported and continuously updated in the status = registers=20 (STAT and OSTAT_).

Offset Diagnostic

Run the offset diagnostic to = determine if there is an offset between the = differential=20 outputs. To run this diagnostic, place the device in = play mode=20 and apply no input signals. The results of this = diagnostic are=20 reported in the OSTAT3./VOS[3:0] (offset voltage = indicator)=20 bits. VOS_ indicates whether the offset voltage is = less or=20 greater than the offset voltage threshold. The = threshold is=20 typically 800mV for the MAX13300/MAX13302 and = typically 1.0V=20 for the MAX13301.

Clipping Diagnostic

Use the clipping = diagnostic to=20 detect clipping outputs. Program the CTRL1.CLVL[1:0] = (clip=20 level) bits for a threshold of either 2%, 4%, 6%, or = 10% THD.=20 Clip indication is provided by the OSTAT0./CLIP[3:0] = (clip=20 indicator) bits. These bits are set to 1 only during = the times=20 when an overdriven output is actually clipping. A = clipping=20 output indictor is available for each output; = OSTAT0./CLIP[3]=20 is for output 3, etc. The open-drain outputs, = active-low CL0,=20 and active-low MUTE_CL1, also provide clip = indication.

Thermal Warning Diagnostic

If the junction temperature=20 exceeds the programmed temperature limit, then a = temperature=20 fault is set immediately. The device does not act upon = a=20 temperature warning to the programmed limit. The = temperature=20 warning self-clears when the temperature drops below = the=20 threshold. If the junction temperature exceeds the = maximum=20 junction temperature of +150=C2=B0C, the device = disables all=20 channels. The digital interface remains active and the = contents of the registers are unchanged. When the die=20 temperature drops below +140=C2=B0C, normal operation = is restored.=20 The programmed temperature limit is set by software = from=20 +110=C2=B0C to +140=C2=B0C in 10=C2=B0C = increments.

Charge-Pump Undervoltage Diagnostic

The=20 MAX13300/MAX13301 drive the high-side=20 FETs with the aid of a charge pump. The charge pump = charges=20 the hold capacitor, C_CHOLD, to 5V at the = end of=20 each switching cycle. When the voltage on = C_CHOLD=20 falls below 3.45V, the device asserts the STAT./CPUV = (charge=20 pump undervoltage indicator) bit and three-states all = outputs.=20 The device deasserts the bit only after voltage on the = hold=20 capacitor rises above 3.75V.

Undervoltage Diagnostic

An undervoltage = monitor=20 detects low voltages on PVDD (< 6V). During an = undervoltage=20 condition, the device three-states all outputs, sets = the=20 STATE./UV (undervoltage indicator) bit to 0, and = asserts the=20 open-drain output active-low FLT_OT.

Overvoltage Diagnostic

The = MAX13300/MAX13301/MAX13302=20 detect overvoltage and load-dump conditions on PVDD = and=20 protect the DMOS devices from damage. During an = overvoltage=20 condition, the device sets the STAT./OV (overvoltage=20 indicator) bit to 0, asserts the open-drain output = active-low=20 FLT/OT, and is latched into standby mode. All = differential=20 outputs are regulated to =C2=BD VPVDD to minimize the = drain-source=20 voltage of the low- and high-side FETs and to prevent=20 breakdown. Once the overvoltage condition is removed, = bring=20 the device out of standby mode by clearing the = CTRL.STBY=20 (standby) bit. The MAX13300/MAX13301 can withstand 50V = load-dump voltage spikes. Battery charger voltages = from 26V to=20 35V can be withstood for up to 1 hour. Figure 7 = illustrates=20 the behavior of the device during a load dump.

Conclusion

The diagnostics capabilities built = into the=20 MAX13300/MAX13301/MAX13302 devices allow the devices = to meet=20 OEM=20 diagnostic requirements. Flexibility built into = specific tests=20 such as load and tweeter diagnostics allow = OEM-specific=20 thresholds to be used.

Related parts =

MAX13300=	4-Channel, = Automotive=20 Class D Audio Amplifier	Free=20 samples
MAX13301=	4-Channel, = Automotive=20 Class D Audio Amplifier	Free=20 samples
MAX13302=	4-Channel, = Automotive=20 Class D Audio Amplifier	Free=20 samples=20

Automatic updates
Would you = like to be=20 automatically notified when new application notes are=20 published in your areas of interest? S= ign=20 up for EE-Mail=E2=84=A2.

Download,=20 PDF format (204kB)
APP 4943: Mar = 31, 2011=20
AN4943, AN 4943, = APP4943,=20 Appnote4943, Appnote 4943=20 =