M.S. KENNEDY CORPORATION 4707 DEY ROAD LIVERPOOL, NY 13088 PHONE: (315) 701-6751 | FAX: (315) 701-6752 http://www.mskennedy.com/ MSK Web Site: Application Note 019 MSK5978RH Evauation Board User's Guide By Bob Abel & Paul Musil, MS Kennedy Corp.; Revised 9/19/2013 Introduction The MSK 5978RH offers low dropout down to 250mV and an output voltage range down to zero volts while offering radiation tolerance for space applications. The low dropout voltage allows increased output current while providing exceptional device efficiency. Because of the increased efficiency, a small hermetic 10 pin ceramic flatpack can be used providing maximum performance while occupying minimal board space. The MSK5978RH is available in two lead options: straight or gull wing. The evaluation board provides a platform from which to evaluate new designs with ample real estate to make changes and evaluate results. Evaluation early in the design phase reduces the likelihood of noise, instability, or other issues, becoming a problem at the application PCB level. This application note is intended to be used in conjunction with the MSK5978RH data sheet and the LT3080 data sheet. Reference those documents for additional application information and specifications. Setup Use the standard turret terminals to connect to the power supply and test equipment. Connect your power supply across the VIN and GND terminals. Leave the VOUT SENSE jumper (J1) installed for proper operation. The CTL pin is used for dual supply operation. Connect the bias supply to the VCTL and GND terminals when using dual supplies. For single supply operation, install J2. Minimum dropout voltage is possible when the MSK5978RH is operated from dual supplies. Connect the output load between the VOUT and GND terminals. Use separate or Kelvin connections to connect input and output monitoring equipment. When measuring output voltage with an oscilloscope probe, the wire from the probe to the ground clip will act as an antenna, picking up excessive noise. For improved results, the test hook should be removed from the tip of the probe. The tip AN019 1 should be touched against the output turret, with the bare ground shield pressed against the ground turret. This reduces the noise induced from external sources. See the Typical Performance Characteristics curves in the data sheet for expected dropout voltage, CTL pin voltage, and current requirements under various conditions. Note: For dual supply operation, a 4.7μF capacitor, C4, from VCTL to ground is recommended to filter the VCTL power supply line. For single power supply operation, the VCTL pin is not independently used, and C4 is not required. There is enough bulk capacitance on the VIN pins. Output Voltage Programming A single resistor (RSET) from the SET pin to ground creates the reference voltage for the internal Error Amplifier. The MSK 5978RH SET pin supplies a constant current of 10µA that develops the reference voltage. The output voltage is simply RSET x 10µA. A low value ceramic capacitor placed across Rset will reduce output noise. Typically, 100pF is all that is required but capacitors up to 1μF can be used. The output voltage rise time will be controlled by the RC time constant RSET x CSET. Figure 1 Efficiency The efficiency of a typical linear regulator is approximated by Vout/Vin. The actual efficiency of an LDO regulator is slightly lower because of bias supplies and ground pin currents. Using separate VIN and VCTL power supplies allows for lower dropout and improved efficiency. The regulator control circuitry is powered by the VCTL input. The dropout of the regulator is determined by the saturation voltage of the output transistor, typically 250mV with a 0.7A ILOAD. The VCTL supply also supplies the base drive current for the output transistor. The VCTL current minus the 10μA SET current is supplied to the load. With separate supplies for VIN and VCTL, power dissipation is reduced and system efficiency improves. Efficiency = 100% x POUT / (PCTL + PIN) Given: AN019 2 POUT = VOUT x IOUT PIN = VIN x IIN PCTL = VCTL x ICTL Where IIN = IOUT – (ICTL – ISET) ICTL can be approximated from the curves (Reference the control pin current curves in the MSK5978RH data sheet for more detail) Input/Output Capacitors The MSK5978RH requires a minimum output capacitor of 10μF with an ESR of 0.5Ω or less. Tantalum or ceramic capacitors are recommended. A larger capacitance value will decrease the amplitude of transients, but will also decrease the bandwidth. The MSK evaluation board utilizes an AVX TAZ series 220uF tantalum output capacitor for increased gain and phase margin across a wide range of applications. The AVX TAZ series was chosen to provide a design starting point using high reliability MIL-PRF-55365/4 qualified capacitors. The input capacitor lowers the input bus impedance as seen by the regulator. The input capacitor requirements increase with increasing input bus impedance and decrease with decreasing impedance. Consideration must also be given to temperature characteristics of the capacitors used. A worst case circuit analysis is recommended for all applications to ensure end of life stability margins are sufficient. Loop Response The plots below show the typical gain and phase response of the default configuration with a 100mA load. 80 200 60 150 Phase Margin = 57° 100 20 50 0 0 -20 -50 Gain Margin = 16.9dB -40 -100 -60 -80 TR2/° TR1/dB 40 -150 103 104 105 106 107 -200 f/Hz TR1: Mag(Gain) AN019 TR2: Phase(Gain) 3 Increased Accuracy The accuracy of the output is dependent on several factors. The internal current source, the tolerance and temperature coefficient of the external resistor RSET, and the output offset voltage. A high accuracy voltage reference such as the MSK109RH may be placed at the SET pin instead of RSET to reduce the errors in output voltage caused by resistor tolerance and drift. (Reference the application notes in the MSK109RH and MSK5978RH data sheets for more detail) Ripple Rejection The chart below shows typical ripple rejection vs. frequency for the evaluation card application circuit at (VIN – VOUT ) = 2V and ILOAD = 500 mA. Ripple rejection measurements are sensitive to noise current in the ground plane. It may be necessary to move the bulk input capacitor to the input line to keep the bulk of the AC input current from influencing the measurement accuracy at the DUT. 0 TR1/dB -20 -40 -60 -80 -100 -120 105 104 103 106 f/Hz TR1: Mag(Gain) Current Limitations The output current limit decreases with increasing input voltage to prevent excessive power dissipation in the device. AN019 4 MSK5978 Evaluation Board Schematic PCB Artwork Top Side Bottom Side Typical Performance Parameter Output Voltage Output Ripple Rejection Output Ripple Rejection Output Noise Output Noise Line Regulation Load Regulation Current Limit Minimum Load Current AN019 Conditions RSET x 10µA, R1 = 120K, 0.1% F = 120 Hz, ΔVIN = 0.5VP-P F = 200kHz, ΔVIN = 0.5VP-P Vin=3V, Vctrl=3V, Rload=2.5Ω, C9 = 0.1µF Vin=3V, Vctrl=3V, Rload=2.5Ω, C9 = 100pF 3V ≤ VIN = VCTL ≤ 25V, VOUT = 1.2V, ILOAD = 1 mA VCTL = VIN = 3.0V, VOUT = 1.2V, 1 mA ≤ ILOAD ≤ 0.7A VCTL = VIN = 5.0V, VOUT = 1.2V VCTL = VIN = 25V Units V dB dB Typical 1.2V(Factory Default) 75 35 µVRMS 31 µVRMS 59 % -0.014 % -0.13 A mA .87 1 5 Bill Of Materials Ref Des U1 C1A C1B C1C C2A C2B C3 C4 C5A C5B C6 C7A C7B C8A C8B C9 R1 AN019 Description Linear Regulator 8050 Ceramic cap 0.1uF 8050 Ceramic cap 0.1uF N/A 4.7 uF 35V Tantalum N/A 8050 Ceramic cap 0.1uF 4.7 uF 35V Tantalum 8050 Ceramic cap 0.1uF 8050 Ceramic cap 0.1uF N/A 220 uF 10V Low ESR Tant. N/A N/A N/A 8050 Ceramic cap 0.1uF Resistor 120K, 1/8W Manufacturer MS Kennedy Corp. AVX AVX Part Number MSK5978RH 08051C104KAT 08051C104KAT AVX AVX AVX AVX AVX AVX TAZG475K035C (CWR09MC475K) 08051C104KAT TAZG475K035C (CWR09MC475K) 08051C104KAT 08051C104KAT AVX TAZH227K010L (CWR29FC227K) AVX 08051C104KAT 6