LABORATORY 2 SPECIFICATION UNITS MIN MAX NOTES. Input Voltage V USB Standard. Input Current ma None

Transcription

1 LABORATORY 2 ASSIGNED: 2/8/18 OBJECTIVE: The purpose of this lab is to give you the opportunity of making a simple power supply circuit containing a DC-DC converter, a linear regulator and an inverting charge pump. In this process, you will have the opportunity to solder physical components on a premade PWB and analyze each circuit s functionality. MINIMUM EQUIPMENT LIST: You will need the following supplies to complete this lab, at a minimum: 1. Multi-meter and test wires 2. Power Supply or a Micro-USB cable and a USB wall adapter 3. Fabricated PWB 4. Electronic Components SYSTEM DESIGN: Most design processes start with a specification (list of requirements) that a circuit is expected to satisfy. In most cases, you would treat your circuit as a black box and determine what outputs you would get for certain inputs. For the circuit you will be building, the specifications can be summarized as: SPECIFICATION UNITS MIN MAX NOTES Input Voltage V USB Standard Input Current ma None Output Voltage [DC-DC] V Output Current [DC-DC] ma Output Voltage [Regulator] V Output Voltage [Regulator] ma DC-DC converter adjustable output voltage Converter branch output current. Output voltage dependent. Regulated branch output voltage. Dependent on DC-DC output Thermally limited based on regulated voltage Output Voltage [Charge Pump] V Charge pump branch output voltage Output Current [Charge Pump] ma - 10 Charge pump branch output current

2 The next design step is to identify the functional elements needed within your circuit in order to satisfy the specifications. Pictorially, this is commonly illustrated in a block diagram like the one shown below for your circuit. Now that the system architecture has been constructed, the next step is to realize each of the different sub-circuits needed to satisfy these functional blocks. This step usually entails researching already developed circuits, or looking for application specific integrated circuits (ASIC s) that may already be designed to provide what you are looking for. Common vendors for ASIC s include: 1. Texas Instruments 2. Analog Devices 3. Linear Technology 4. Maxim Semiconductor After the parts have been selected, the next step is to construct a schematic. This is a wiring diagram that interconnects all the components in such a way that the specifications for your system will be satisfied. You will see in the schematic illustrated below that actual component values have been identified while preserving the sub-circuits detailed in the block diagram.

3 Functionally, the main input power source is provided at J1 which for this design is a +5.0V input supply provided by a USB interface. The LED lamp is tied to the main input supply, which will be illuminated whenever the input is energized. Afterwards, the power source is split two ways, one branch going to the DC-DC converter which steps up the +5.0V supply to an adjustable range up to +24.5V, while the second branch goes to a negative supply charge pump that produces a -5.0V supply. The third sub-circuit is a linear regulator branch tied to the DC-DC converter output and provides an adjustable output voltage ranging between +2.2V through +6.6V. The core elements realized for the different functional blocks are realized using the MC34063, the LM317 and the TC7660 integrated circuits, which have their own system functionality on the chip. This greatly simplifies your design requirements because all you will need to do is include the supporting passive components (ie: capacitors, inductors and resistors) around these IC s in order to make them work the way you need. From the schematic, a Bill-Of-Materials (BOM) can be generated, which is a list of all the parts that you have selected for your design. This list will help both in purchasing the parts and in assembling the circuit board. Schematics and BOM s are created using a schematic capture tool (ie: Cadence Orcad)

4 which allows you to easily export the BOM after you define all the part properties. Key properties include manufacturer, part number, value, size and reference designator. DESCRIPTION MFG PART NUM VALUE SIZE REFERENCE QTY DIP-8 Socket TE Connectivity DIP-8 J2, J3 2 Capacitor Nichicon UVR1H101MPD 100uF Radial C6 1 Capacitor Nichicon UVR1V331MPD 330uF Radial C3 1 Capacitor Nichicon UVR1H100MDD 10uF Radial C7 1 Inductor Bourns RLB KL 180uH Radial L1 1 Diode Diodes 1N5819-T Shottky Axial D2 1 Capacitor Vishay H152K29X7RL63J5R 1500pF Radial C1 1 Micro-USB Amphenol LF - Micro-USB J1 1 Potentiometer Bourns RK09K113004U 10k Thru R9, R10 2 LED Cree C5SMF-GJF-CV0Y0791 Green Radial D1 1 Capacitor Murata GRM21BR61E106KA73L 10uF 805 C4, C5 2 Inverter Microchip TC7660EPA Inverter DIP-8 U2 1 Boost TI MC34063AP Boost DIP-8 U3 1 LDO TI LM317LILPR LDO TO-92 U1 1 Resistor KOA Speer MF1/4DC1800F 180 Axial R8 1 Resistor KOA Speer MF1/4DC5902F 59k Axial R6 1 Resistor KOA Speer MF1/4DC3161F 3.16k Axial R5 1 Resistor KOA Speer MF1/4DC80R6F 80.6 Axial R1 1 Resistor TE Connectivity FRN25JR Axial R4 1 Resistor KOA Speer MF1/4DCT52R3161F 3.16k Axial R2 1 Resistor KOA Speer MF1/4DCT52R2001F 2k Axial R3 1 Resistor Panasonic MF1/4DCT52R1001F 1k Axial R11 1 THEORY OF OPERATION: Now that we have developed the circuits, lets analyze how they work and address key design details about them. To do this, it will be necessary to pull up the manufacturer datasheets for the three integrated circuits: MC34063A, the LM317 and the TC7660. Internet searches through popular search engines can help, but most times it is simply easier to go directly to the manufacturer s website and perform a local search under the part number you are searching for. Unfortunately, every manufacturer has their own datasheet format and presentstheir own types of data. This can often make going through datasheets a cumbersome task, but more experience will help you extract the important information you need to make the right design decisions. INVERTING CHARGE PUMP (TC7660) Lets start with the inverting charge pump, the TC7660 from the manufacturer Microchip. In this case, the manufacturer has provided 20-pages of information to assist in your design decision on whether this part will work for your application. Common design driving considerations when selecting power management devices are (voltage, current, power and temperature), or more explicitly put:

5 1. What s the minimum and maximum input voltages the part can handle without getting damaged 2. What s the output current capabilities 3. What s the thermal resistance 4. What s the maximum operating temperature or alternatively the maximum junction temperature Please take a moment to go through the datasheet and answer the questions outlined in the end of this section. To assist, you may note that the voltages and currents are readily found within the datasheets, but determining the parts actual operating temperatures requiresspecific calculations derived based on how you intend to use the parts. For DC-DC converters, you would determine how much power you expect to deliver to a load (some other circuit which may eventually be connected to it). Because energy is conserved, power going to the load must be provided by the source, but since no part is 100% efficient, the input power will be slightly higher to also account for power dissipated within the part. Note that dissipated power causes heat which must be limited by your design below the manufacturer s maximum ratings. EXAMPLE: If a DC-DC converter is 90% efficient and you expect to deliver +5V and 100mA to your load, the dissipated power within the device is 55mW. This means that the input supply must provide 555mW of power to the DC-DC converter. If the part has a thermal resistance of 100 C/W, then this would cause a temperature rise of +5.5C above the air temperature. One unwanted side-effect with most DC-DC converters is that they can be inherently noisy. Noise in electronic circuits typically refers to unwanted voltages and/or currents that are present in addition to the DC voltage and/or current your circuit provides. Mathematically, this can be expressed as: Vout = VDC + Vnoise Where Vnoise is an AC component with many frequencies DC-DC CONVERTER (MC34063A) Next, lets take a look at the MC34063A from the manufacturer Texas Instruments. In this case, the manufacturer has provided 30-pages of information to assist in your design decision on whether this part will work for your application. As with the charge pump, common design driving considerations when selecting power management devices are voltage, current, power and temperature. Please take a moment to go through the datasheet and answer these questions (outlined in the end of this section). Please take a moment to go through the datasheet and answer the questions outlined in the end of this section. To assist, you may note that the voltages and currents are readily found within the datasheets, but determining the parts actual operating temperatures requires specific calculations derived based on how you intend to use the parts.

6 Your circuit will configure this chip as a step-up converter that will take the +5V input and step it up to a voltage reaching around +25V. Another name for step-up converters is boost converters. The baseline circuit application is illustrated on Page-13 of the datasheet with all the associated design formulas detailed in Page-14. The design formulas help you select the size of the additional passive components needed to make the chip meet your requirements. A differentiating feature of this DC-DC converter is that it has an ability to let the user adjust the output voltage even though the input voltage remains constant. It is this feature that gives you the ability of having an adjustable power supply from your circuit. This is facilitated through a feedback loop that takes the output voltage, scales it through a resistive divider network and compares the scaled version to an internal reference voltage. The chip then automatically adjusts the output voltage appropriately until the difference between the scaled output voltage and the internal reference voltage is zero (we will cover this in more detail when covering opamps). Looking at Page-14, you will note that the output voltage set-point is a function of resistors R1 and R2 and is related by the formula: Vout = 1.25(1 + R2/R1) Where 1.25V is the internal reference voltage and R2 and R1 are resistor values you determine based on your design needs. Another notable detail on DC-DC converters is that they are considered constant power sources. This means that depending on the output power your load circuit requires, the input power provided to the DC-DC converter will be the same plus efficiency losses. LINEAR REGULATOR (LM317) Lastly, lets take a look at the LM317 from the manufacturer Texas Instruments. In this case, the manufacturer has provided 29-pages of information to assist in your design decision on whether this part will work for your application. Linear regulators are very different in operation to the DC-DC converters previously discussed, though consideration to voltage, current, power and temperature remains the same. Please take a moment to go through the datasheet and answer these questions (outlined in the end of this section). The voltages and currents are found within the datasheets, while determining the operating temperatures and comparing them to the specified maximums require calculations around how you intend to use the parts. In the case of linear regulators, you would determine the dissipated power by calculating the worst case voltage drop between the input and output terminals with respect to the specified load current. EXAMPLE: If a linear regulator has a thermal resistance of 100 C/W, and it regulates a +12V supply down to +5V with a load current of 100mA, then the dissipated power within the device will be 700mW causing a temperature rise of +70C above the air temperature.

7 Our circuit will configure this chip as an adjustable voltage source. The baseline circuit application is illustrated on Page-8 of the datasheet along with all the associated design formulas. As with the MC34063A, this linear regulator has an ability to let the user adjust the output voltage even though the input voltage remains constant. It is this feature that gives you the ability of having an adjustable power supply from your circuit.this is facilitated through a feedback loop that takes the output voltage, scales it through a resistive divider network and compares the scaled version to an internal reference voltage. The chip then automatically adjusts the output voltage appropriately until the difference between the scaled output voltage and the internal reference voltage is zero (we will cover this in more detail when covering op-amps). Looking at Page-8, you will note that the output voltage set-point is a function of resistors R1 and R2 and is related by the formula: Vout = 1.25(1 + R2/R1) + Iadj * R2 Where 1.25V is the internal reference voltage, R2 and R1 are resistor values you determine based on your design needs and Iadj is the leakage current from the adjustment pin of the chip (unwanted design consideration) and is published in the datasheet Another notable detail on linear regulators is that they are considered constant voltage sources. This means that the regulator will try to hold the output voltage constant for different load current conditions. However, the load current will be equal to the input current provided to the chip resulting in varying dissipated power levels within the chip for a varying output voltage and constant load currents. As with efficiency losses associated with DC-DC converters, an unwanted byproduct of linear regulators is the drop-out voltage. Some higher quality (and more expensive) devices have very small drop-out voltages which allow you to run the output voltage much closer to the input voltage. A significant advantage for using linear regulators is that they provide low noise clean output power sources. In the case of the LM317, this part can provide a typical ripple rejection of 80dB, meaning that with unwanted input AC signals (from sources like the DC-DC converter), this part will reduce their magnitude to one-hundred-millionth the size on the output of the part.

8 QUESTIONS: 1. Describe: a. The theory of operation for the three IC s b. Intuitively explain what types of applications they would be useful in c. Why is there a switching frequency associated with DC-DC converters 2. What is the minimum and maximum operating voltage a. For the Microchip TC7660 b. For the Texas Instruments MC34063A c. For the Texas Instruments LM What is the maximum output current capability a. For the Microchip TC7660 b. For the Texas Instruments MC34063A c. For the Texas Instruments LM What is the thermal resistance a. For the Microchip TC7660 b. For the Texas Instruments MC34063A c. For the Texas Instruments LM What is the minimum dropout voltage for the linear regulator a. Describe what this property is and why it is important when designing a circuit with a linear regulator 6. What is the typical efficiency of the two DC-DC converters a. Describe what this property is and why it is important when designing a circuit with DC-DC converters 7. What is the maximum operating or junction temperature a. For the Microchip TC7660 b. For the Texas Instruments MC34063A c. For the Texas Instruments LM In the case of the MC34063A DC-DC converter, if the chip is running at 90% efficiency, you have set the output voltage to +24.5V and have a load current of 100mA, what is the input power and input current requirements to your circuit? 9. For the LM317 linear regulator, if you have set the output voltage to +2.2V, the DC-DC converter is set to an output voltage of +24.5V and is running at 90% efficiency and you have connected a 20mA circuit load to the output of your regulator, what is the input power and current requirements to your circuit? 10. If the ambient temperature your circuit will operate is +20C (room temperature), determine the operating temperature of the chip at: a. For the Microchip TC7660 operated at the maximum specified output current b. For the Texas Instruments MC34063A operated at +24.5V and 100mA load current c. For the Texas Instruments LM317 operated at +24.5V input and +2.2V output at 100mA d. Calculate the margin between the specified maximum operating temperatures and the calculated operating temperatures. For any of the parts that exceed the maximum operating temperatures, determine the operating conditions that must exist to keep the temperature below maximum limits. This is commonly referred to as a derating factor

9 BUILDING YOUR CIRCUIT Now that you have a better understanding of how your circuit has been designed to achieve the specifications, how the components work together and key design considerations, you are ready to assemble each part on a circuit board. To do this, you will need a printed-wiring-board (PWB) designed for this application in addition to the parts. You should be receiving a bag kit with all the components listed on the BOM. You will need to carefully identify the component values, and in some cases the component polarity prior to assembling your PWB. You can install the parts one-by-one onto your PWB by inserting the leads of the parts through the PWB and bending the leads on the back side by approximately 45-degrees. This helps keep the part from slipping out of the board. You may note that the back side of the board is commonly the side with the annular rings land-pad that the leads solder onto. IDENTIFYING RESISTORS In the case of the resistors, there are color bands that help identify the value of the component. The first three bands indicate the value where the first two are the prefix number and the third band indicates the multiplier. Internet searches can help you determine the color and corresponding numerical value for axial resistors. You can also use the multi-meter to measure the resistance of the part. EXAMPLE: A resistor with color bands RED + BLACK + RED corresponds to 20 x 1x10 2 = 2k-ohm IDENTIFYING CAPACITORS RADIAL CERAMIC RADIAL ELECTROLYTIC SURFACE MOUNT (SMT) CERAMIC

10 You will note that your kit will have two types of capacitors. The first type is a ceramic which looks like a beige disk with numbers on the front (thru-hole) or small chip looking parts. The second type is the aluminum electrolytic which looks like a small can with two leads protruding from one side. The ceramic capacitors are non-polarized, which means that they can be installed into the circuit in either orientation. The aluminum electrolytic capacitors included in your kit are polarized, which means that their orientation within the circuit is very specific. You will note a (-) stripe on one side of the capacitor which guides you to the negative terminal lead on the bottom of the package. It is EXTREMELY IMPORTANT that the negative terminal is connected to the ground plane on the PWB. Installing a polarized capacitor in the circuit backwards is reverse biasing the part, which can cause it to EXPLODE and may result in very serious injuries. The markings on the side of most aluminum electrolytic capacitors indicate the capacitance value (in micro-farads) and maximum working voltage. Exceeding the working voltage on the component can also cause the part to explode and must be avoided. Though ceramic capacitors also have a maximum working voltage, typical markings only indicate capacitance.internet searches can help you determine the corresponding numerical value for ceramic capacitors. EXAMPLE: A marking of 103 on a ceramic capacitor reflects a capacitance of 10,000pF IDENTIFYING INDUCTORS Inductors are non-polarized circuit elements which do not require a specific installation orientation within your circuit. As with ceramic capacitors, some inductors have marking codes which indicate its inductance.internet searches can help you determine the corresponding numerical value for the inductor. IDENTIFYING DIODES The LED and Shottky diodes included in your kit are designed to allow current to flow exclusively in one direction and have a specific polarity in order for current to flow in the specific direction.

11 LED DIODE SHOTTKY DIODE CIRCUIT POLARITY You can determine the polarity of the Shottky by looking at the white band across the part. The lead closest to this band is the cathode (negative terminal). Alternatively, you can measure the polarity using the multi-meter. To test the part, configure the multi-meter to diode measurement mode and probe across its terminals. The negative terminal will be tied to the black lead on the multi-meter. IDENTIFYING POTENTIOMETERS Potentiometers are three terminal devices that allow you to adjust the resistance between two terminals in response to rotating the wiper. Because potentiometers are effectively a resistor, there are no polarity or orientation requirements for the component other than any mechanical attachment considerations. In general, the outer two terminals are a fixed resistance based on the part selected (ie: 10k-ohm), however the resistance between the two adjacent pins will change based on the angle the wiper shaft is turned. IDENTIFYING THE INTEGRATED CIRCUIT SOCKET Your kit will include a dual-inline-package DIP-8 socket. These are components that allow you to quickly remove integrated circuits (ie: MC34063A) with a DIP-8 package from your circuit without having to touch the soldering iron. The DIP-8 sockets included in your kit are not dependent on orientation, though you may notice that a half-circle notch is removed on one of the sides. This is an assembly aid that helps you know that when you install the part into the socket, that PIN-1 is on the same side as the notch.

12 IDENTIFYING THE INTEGRATED CIRCUITS Your kit includes the MC34063A the TC7660 integrated circuits. Since these are parts have very specific functionality that are dependent on the supporting passive components discussed earlier, orientation matters. Most packages denote PIN-1 by a circle printed or scribed on the top of the part. Part numbering starts with PIN-1 in the upper left corner and counts up in a counter-clockwise orientation around the part. See the datasheet if you need more specific orientation. The LM317 included in your kit is a TO-92-3 package. PIN-1 is oriented on the left with respect to the flat face of the package facing you. See the datasheet if you need more specific information. TO-92-3 DIP-8 ASSEMBLY OF THE PWB Now that you have studied how to distinguish among the different components included in your kit, you are ready to start installing the parts on your PWB. You will need to correlate the assembly drawing detailed below to the BOM in order to identify the part to be installed and where it needs to be installed on the PWB. This is accomplished by linking the reference designator detailed on the assembly drawing to the BOM (ie: R1, C1, L1, etc.). To identify the correct part, make the appropriate inspections or measurements using the multi-meter among the parts included in your kit. For all of the resistors, measure and record the actual resistance values in-case you may need to troubleshoot your circuit later. This must be done before the parts are installed in your circuit.

13 PWB ASSEMBLY DRAWING AND LAYOUT (TOP VIEW) Palomar College ENGR210

14 DESCRIPTION MFG PART NUM VALUE SIZE REFERENCE QTY DIP-8 Socket TE Connectivity DIP-8 J2, J3 2 Capacitor Nichicon UVR1H101MPD 100uF Radial C6 1 Capacitor Nichicon UVR1V331MPD 330uF Radial C3 1 Capacitor Nichicon UVR1H100MDD 10uF Radial C7 1 Inductor Bourns RLB KL 180uH Radial L1 1 Diode Diodes 1N5819-T Shottky Axial D2 1 Capacitor Vishay H152K29X7RL63J5R 1500pF Radial C1 1 Micro-USB Amphenol LF - Micro-USB J1 1 Potentiometer Bourns RK09K113004U 10k Thru R9, R10 2 LED Cree C5SMF-GJF-CV0Y0791 Green Radial D1 1 Capacitor Murata GRM21BR61E106KA73L 10uF 805 C4, C5 2 Inverter Microchip TC7660EPA Inverter DIP-8 U2 1 Boost TI MC34063AP Boost DIP-8 U3 1 LDO TI LM317LILPR LDO TO-92 U1 1 Resistor KOA Speer MF1/4DC1800F 180 Axial R8 1 Resistor KOA Speer MF1/4DC5902F 59k Axial R6 1 Resistor KOA Speer MF1/4DC3161F 3.16k Axial R5 1 Resistor KOA Speer MF1/4DC80R6F 80.6 Axial R1 1 Resistor TE Connectivity FRN25JR Axial R4 1 Resistor KOA Speer MF1/4DCT52R3161F 3.16k Axial R2 1 Resistor KOA Speer MF1/4DCT52R2001F 2k Axial R3 1 Resistor Panasonic ERJ-6ENF1001V 1k 805 R11 1 You can turn on your soldering iron, but before you begin soldering your parts, you will need to wait some time for the tip to reach reflow temperatures. This temperature has been reached when you put solder on the tip of the iron and it melts. But, since your soldering irons have an adjustable temperature range, you will want the temperature setting just high enough for solder to flow. Having a soldering tip that is too hot can damage components and the PWB and make soldering more difficult when the flux burns on the tip. You will want to have solder near-by, solder flux, a sponge with water, solder wick and tweezers. The solder flux is a compound that helps the solder flow around the component and the PWB more quickly and evenly. The wet sponge helps wipe off burnt flux from the tip of the iron. The tweezers help you align the part prior to soldering and solder wick will help you remove solder from the PWB if you need to rework your board. Starting with one of the resistors, insert the part through the appropriate thru-holes on the PWB until the package sits flush with the board. You will need to bend the leads to fit the land-pad outline on the PWB and bend the leads on the back side of the PWB at a 45-degree angle. NOTE: Due to the plastic housing design, please install the potentiometers (R9 and R10) and the LED (D1) from the back side of the board. This is the side that has the ground plane. When soldering the metal-to-metal interface between the lead of the part and the land-pad on the PWB, you will want to touch the iron to both surfaces and heat them up to solder melting temperature. After a few seconds, tab a bit of solder on the metal-to-metal interconnect being careful not to touch the solder on the iron directly. This is because the goal of soldering is to let solder flow on both the metal surfaces and not onto the iron. Melting the solder directly on the iron could result in a cold solder joint which could cause unpredictable behavior from your circuit.

15 Palomar College ENGR210 Another word of caution when soldering, make sure you use enough solder to completely encircle the land-pad on the printed circuit board, or to have a good metal-to-metal attachment. In doing so, be careful not to cause a blob of solder to accumulate at the attachment point. Note the drawing below which shows what a good and bad solder joint may look like. The Good TheBad

16 QUESTIONS: Now that you have built your circuit, it will be necessary to test its functionality and ensure that it is working to specification. The following questions below can be re-tabled as a test-data-record TDR, which will help you ensure that it is operating correctly. If there are problems, you will be able to identify what the symptoms, which will help you in taking a closer look at the design or assembly in-case you need to troubleshoot the problems. Before you install the USB connector, it is a good idea to get a sense of how much current your circuit is pulling (ie: the load your circuit will present to the power supply). Please use a laboratory power supply set at +5.0V with a current limit set at 200mA. Solder a wire just after PIN-1 on the USB connector (on the large copper pad between C6 and R4) and another wire to the ground plane on the circuit board (on the large copper pad between C6 and D1). 1. Record all of the resistor values prior to installation into your circuit a. R1 through R10 2. Measure how much current the +5.0V power supply is providing to your circuit. You will need to install test wires to bypass the USB connector and power your circuit through the lab power supply. If the power supply is current limiting (>200mA), turn off the power supply and inspect the board for a potential short circuit condition. 3. Measure the input supply voltage present to your circuit USB_[+5.0V] a. Is the green LED illuminated? 4. Measure the output voltage of the charge pump SUPPLY_[-5.0V] 5. Measure the output voltage of the DC-DC converter SUPPLY_[+6.8V to +24.5V] a. Turn the wiper on the potentiometer clockwise until it stops and record the voltage b. Turn the wiper counter-clockwise until it stops and record the voltage c. Turn the wiper to mid-point of its turning range and record the voltage d. For the extreme two voltages, record the error between the specified voltage and the measured voltage e. If you were to modify your circuit to achieve the exact values specified, what components would you change and what would the values need to be 6. Measure the output voltage of the linear regulator SUPPLY_[+2.2V to +6.6V] a. Turn the wiper on the potentiometer clockwise until it stops and record the voltage b. Turn the wiper counter-clockwise until it stops and record the voltage c. Turn the wiper to mid-point of its turning range and record the voltage d. For the extreme two voltages, record the error between the specified voltage and the measured voltage e. If you were to modify your circuit to achieve the exact values specified, what components would you change and what would the values need to be