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Mechanical Data and Layout Considerations

SLVA075

6.2

Layout Considerations

The following four points should be followed at the layout to ensure trouble-free
operation:

•

Use a blocking capacitor of 100 nF between supply voltage and ground.

•

Place the external capacitor near the device.

•

If the circuit includes a device with a high current consumption, keep the
common ground wire small due to the danger of a floating ground. This can
be achieved by keeping the ground line separated as long as possible
(star-shape connection).

•

Locate the supervisor circuit in an interference-free environment.

The following two figures show layouts with the TPS3801 and TPS3809. The
used capacitor is in a 0805-package ( L x W x H : 2 mm 1.25 mm 0.45 mm).

GND

RESET

1 mm

Figure 26. Layout Suggestion Using a

TPS3801

Figure 27. Layout Suggestion Using a

TPS3809

GND

RESET

1 mm

Содержание TPS3801

Страница 1: ...TPS3801 09 Smallest SVS for Monitoring DSPs and Processors September 1999 Mixed Signal Products Application Report SLVA075 ...

Страница 2: ...CONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH PERSONAL INJURY OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE CRITICAL APPLICATIONS TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED AUTHORIZED OR WARRANTED TO BE SUITABLE FOR USE IN LIFE SUPPORT DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER S RISK In order to ...

Страница 3: ...set Input 11 4 3 Minimum Conditions for Triggering a Manual Reset 11 4 4 Saving Current While Using the Manual Reset Function 12 4 4 1 Current Flow Off the Manual Reset Input 12 4 4 2 Lateral Current From VDD to GND 12 5 Applications 14 5 1 A TPS3801 Supervises a DSP 14 5 2 Switching the Power Supply With a TPS3801 14 5 3 Keeping a Low Signal at Reset Output for Voltages Below 1 1 V 16 5 4 Supervi...

Страница 4: ...t Input 12 15 Internal Realization of the Manual Reset Circuit 12 16 Lateral Current in Dependence of the Voltage at a CMOS Input Stage 13 17 TPS3801 Supervises the TMS320LC542 DSP 14 18 System Power Control With the TPS3801 15 19 Measurements of Switching Power With A TPS2051 16 20 An Additional Resistor Ensures a Valid Reset Down to 0 V 16 21 Higher Accuracy Supervision of 3 6 V 18 22 Measuremen...

Страница 5: ...to the RESET input to deliver the necessary reset pulse After switching on the power supply this circuit keeps the logic level at the RESET input low for a time determined by the capacitor and resistor values This delay time required by the system to complete the initialization allows the power supply to become stable However this circuit has some disadvantages In cases of brief reductions of the ...

Страница 6: ...set signal active for a defined time after the supply voltage has returned to its nominal value to ensure proper initialization of the microprocessor or DSP The Texas Instruments TPS3801 and TPS3809 families of integrated circuits fulfill the requirements described above without requiring additional external components 2 Circuit Description This section describes the TPS3801 and TPS3809 devices an...

Страница 7: ...et input MR MR 5 Digital input low active Manual reset Input to trigger a Reset pulse by an external component or an external signal source RESET 3 2 Digital output low active Output for triggering a reset at the connected controller or DSP shows the state of the internal reset logic VDD 4 3 Positive power supply Supplies the circuit with voltage and input for the voltage supervision 2 5 Block Dia...

Страница 8: ...R1 R2 Reference Voltage or 1 137 V TPS3809 TPS3801 MR VDD GND RESET TPS3801 Only Figure 4 Block Diagram of TPS3801 and TPS3809 2 6 Basic Timings Figure 5 summarizes the two reasons for an active reset at a TPS3801 The behavior of the TPS3809 is the same without the manual reset input If the supply voltage is below 1 1 V there is no defined reset signal If the supply voltage increases above 1 1 V t...

Страница 9: ... Description 5 TPS3801 09 Smallest SVS for Monitoring DSPs and Processors For VDD 1 1 V Undefined Behavior of RESET Output td td td t t t VDD MR RESET Vnom VIT 1 1 V 1 0 1 0 Figure 5 Timing Diagram of TPS3801 ...

Страница 10: ...uld be completed The difference between the negative going and the positive going threshold voltage is called hysteresis Vhys VIT VIT Vhys The reason for the hysteresis is to avoid toggling of the reset output if the voltage is noisy For a better understanding a timing diagram with these parameters is given RESET Goes High After Delay Time of Typical 200 ms RESET Goes Low VSENSE VCC VIT VIT t Vhys...

Страница 11: ...Drop on the Supply Line To demonstrate the typical operation of an SVS the following measurement has been made The measurement circuit of Figure 7 has been used Waveform Generator 100 nF VDD GND MR RES TPS3801 50 Oscilloscope 39 nF 1 MΩ Figure 7 Measurement Circuit for Measuring the Reaction of a Voltage Drop The waveform generator supplies the supervisor and generates the voltage drop to trigger ...

Страница 12: ... in the process The oscillator is built up internally with an RC network 3 3 Threshold Overdrive Versus Pulsewidth The datasheet specifies that a voltage drop of 3 µs to at least 200 mV below the negative going threshold voltage VIT must trigger a reset pulse But what happens with a shorter but deeper drop This question is answered with the measurements shown in Figure 9 and Figure 10 The x axis s...

Страница 13: ...cessors 0 0 1 0 2 0 3 0 4 0 5 0 0 1 2 3 4 5 6 7 8 9 10 Voltage V VIT 4 55 V t Time µs 1 1 Figure 9 Breakdown Voltage versus Pulsewidth at a TPS380xI50 0 0 0 5 1 0 1 5 2 0 2 5 0 1 2 3 4 5 6 7 8 9 10 Voltage V 1 1 t Time µs VIT 2 25 V Figure 10 Breakdown Voltage versus Pulsewidth at a TPS380xJ25 ...

Страница 14: ...e RC network VDD RESET GND TPS3801J25 C 100 nF R Figure 11 TPS3801 With a Low Pass Filter at VDD Terminal Care has to be so taken that the additional resistor does not alter the threshold voltage too much The threshold voltage is determined by the internal voltage divider like shown in the block diagram in Chapter 2 A resistor of R1 10 kΩ in the RC combination raises the threshold voltage by 1 5 i...

Страница 15: ...al pullup resistor unnecessary This input can be left floating if it is not used 4 2 A Measurement of Low Pulse at the Manual Reset Input For a better illustration a measurement of a low pulse of 100 ms at manual reset and the resulting reset pulse is shown in Figure 13 The measurement has been made at a TPS3801I50 MR and RESET MR and RESET RESET Figure 13 Reset Pulse Triggered by Manual Reset 4 3...

Страница 16: ...hould be triggered with a low pulse at manual reset it should be a short pulse Reset Logic 30 kΩ VDD MR VMR Voltage Source TPS3801 IMR Figure 15 Internal Realization of the Manual Reset Circuit The current out of the manual reset terminal depends on the difference between VDD and VMR and can be easily calculated with equation 2 IMR VDD VMR 30 kW 4 4 2 Lateral Current From VDD to GND There is anoth...

Страница 17: ... 09 Smallest SVS for Monitoring DSPs and Processors 50 0 0 0 50 0 100 0 150 0 200 0 250 0 300 0 350 0 0 00 1 00 2 00 3 00 4 00 5 00 VMR V I lat µ A Figure 16 Lateral Current in Dependence of the Voltage at a CMOS Input Stage ...

Страница 18: ...7 TPS3801 Supervises the TMS320LC542 DSP 5 2 Switching the Power Supply With a TPS3801 Figure 18 illustrates an application to turn system power on and off with a TPS3801 The TPS2051 a power distribution switch of Texas Instruments has a high active enable input so that it can be directly connected to the reset output of the supervisor Typically the TPS2051 has RDSon of less than 100 mΩ To keep th...

Страница 19: ... µA For more detailed information The datasheet can be found on the WWW at the address http www s ti com sc psheets slvs172a slvs172a pdf An application report with the title TPS202x 3x and TPS204x 5x USB Power Distribution is available at http www s ti com sc psheets slva049 slva049 pdf Figure 19 shows the three most important voltages of the application example The load was a 3 3 kΩ resistor Nor...

Страница 20: ...the reset input of the connected device is floating and this state should be avoided Although most microcontrollers and DSPs do not work at voltages below 1 1 V there are systems that requires a correct reset signal down to 0 V To solve this problem a pulldown resistor of 100 kΩ is placed between the reset output and ground The disadvantage of this solution is a steady current flow during inactive...

Страница 21: ...age of 3 6 V 5 4 1 Threshold Voltage Change Application 1 In the following descriptions and calculations the threshold voltage of Vin is called Vtrip The fixed threshold voltages of the devices are named as VIT Resistors of the E96 series with a tolerance of 1 should be taken to achieve an optimum accuracy for the threshold voltage A hundred times higher current through the voltage divider than th...

Страница 22: ...6 V This application has been built up and tested The result of the evaluation is the measurement plot in Figure 22 The threshold voltage of Vin has been at 3 61 V Measurements 0 5 0 0 5 1 1 5 2 2 5 3 3 5 4 4 5 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 time s voltage V VVDD VRESET Vin Vtrip 3 61 V V IT 2 25 V t delay 217 ms Figure 22 Measurement Plot of the 3 6 V Voltage Supervision ...

Страница 23: ...ange Application 2 Now the current through R4 is only ten times higher than the device current at VDD 2 25 V it is 100 µA Therefore the device current cannot be neglected in the calculation The adjusted threshold voltage should be again 3 6 V R4 can be calculated as follows R4 VIT IQ 2 25 V 100 mA 22 5 kW To choose a E96 series value R4 22 6 kW The current into the device is 10 µA at VDD 2 25 V so...

Страница 24: ...s and temperature of 7 µA to 13 µA PARAMETER MINIMUM TYPICAL MAXIMUM ISupply 7 µA 10 µA 13 µA RDEVICE 173 kΩ 225 kΩ 321 kΩ R3 12 28 kΩ 12 4 kΩ 12 52 kΩ R4 22 37 kΩ 22 6 kΩ 22 83 kΩ R4equivalent 19 81 kΩ 20 54 kΩ 21 31 kΩ VIT 2 20 V 2 25 V 2 30 V Vtrip 3 47 V 3 60 V 3 76 V Worst case 1 Vtripmin R3 min R4equivalent max R4equivalent max VIT min 12 28 kW 21 31 kW 21 31 kW 2 20 V 3 47 V Worst case 2 Vt...

Страница 25: ...ions are in millimeters 0 65 0 15 0 30 1 35 1 15 2 20 2 00 2 20 1 80 GND GND RESET V MR DD TPS3801 Figure 24 Linear Dimensions of SOT323 Package The TPS3809 is available in the SOT23 3 package DBV 3 2 50 3 00 1 50 1 80 2 70 3 10 0 50 0 30 0 95 GND RESET V DD TPS3809 Figure 25 Linear Dimensions of SOT23 3 Package More detailed information about mechanical data can be found on the internet on the pa...

Страница 26: ...rrent consumption keep the common ground wire small due to the danger of a floating ground This can be achieved by keeping the ground line separated as long as possible star shape connection Locate the supervisor circuit in an interference free environment The following two figures show layouts with the TPS3801 and TPS3809 The used capacitor is in a 0805 package L x W x H 2 mm 1 25 mm 0 45 mm GND ...

Страница 27: ... manual reset function which offers a lot of possibilities in applications This device has a typical supply current of less than 20 µA so that it is well suited for battery powered systems It is characterized for a temperature range from 40 Cto85 C ApartfromtherecommendedcapacitorbetweenVDD andground no external components are needed 8 References 1 Data Sheet of TPS3801xxx TPS3809xxx Literature Nu...

Страница 28: ...24 SLVA075 ...

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