19-4781; Rev 0; 5/00 MAX1710 Evaluation Kit The MAX1710 evaluation kit (EV kit) demonstrates the data sheet’s standard 7A notebook CPU application circuit (see MAX1710/MAX1711 data sheet). This DC-DC converter steps down high-voltage batteries and/or AC adapters, generating a precision, low-voltage CPU core VCC rail. The circuit was designed for a 7V to 24V battery range, but accommodates from 4.5V to 24V. Some parameters, such as load-transient response and maximum thermal load capability, may be degraded by going outside the 7V to 24V range. The continuous output current rating, based on worst-case MOSFET RDS(ON), heat sinking, and other thermal stress issues, is 5.5A at TA = +70°C. This EV kit is a fully assembled and tested circuit board. It also allows the evaluation of the MAX1711. Ordering Information PART TEMP. RANGE MAX1710EVKIT 0°C to +70°C IC PACKAGE 24 QSOP NOTE: To evaluate the MAX1711, request a MAX1711EEG free sample with the MAX1710 EV Kit. Features ♦ High Speed, Accuracy, and Efficiency ♦ Fast-Response QUICK-PWM™ Architecture ♦ 7V to 24V Input Voltage Range ♦ 1.25V to 2V Output Voltage Range ♦ 7A Peak Load-Current Capability (5.5A Continuous) ♦ 93% Efficient (VOUT = 2V, VBATT = 7V, ILOAD = 4A) ♦ 300kHz Switching Frequency ♦ No Current-Sense Resistor ♦ Remote GND and VOUT Sensing ♦ Power-Good Output ♦ 24-Pin QSOP Package ♦ Low-Profile Components ♦ Fully Assembled and Tested Component List DESIGNATION QTY C1–C4 C1–C4 (ALTERNATE) DESCRIPTION 4 4.7µF, 25V ceramic capacitors Taiyo Yuden TMK325BJ475K 4 10µF, 25V ceramic capacitors Tokin C34Y5U1E106Z or United Chemi Con/Marcon THCR50E1E106ZT 3 470µF, 6.3V, 30mΩ low-ESR tantalum capacitors Kemet T510X477M006AS C8 1 10µF, 6.3V ceramic capacitor Taiyo Yuden JMK325BJ106MN or TDK C3225X5R1A106M C9 1 0.1µF ceramic capacitor C11, C12 2 0.22µF ceramic capacitors C14 1 470pF ceramic capacitor C15 1 1µF ceramic capacitor C16, C17, C18 0 Not installed D1 1 2A Schottky diode SGS-Thomson STPS2L25U or Nihon EC31QS03L 1 100mA Schottky diode Central Semiconductor CMPSH-3 Hitachi HRB0103A C5, C6, C7 D2 DESIGNATION QTY DESCRIPTION D3 1 1A Schottky diode Motorola MBRS130LT3, Nihon EC10QS03, or International Rectifier 10BQ040 Hitachi HRF22 D4 1 200mV switching diode Central Semiconductor CMPD2838 1 2µH power inductor Panasonic ETQP6F2R0HFA, Coiltronics UP4B-2R2, or Coilcraft DO5022P-222HC 1 N-channel MOSFET International Rectifier IRF7807, Fairchild FDS6612A, or Siliconix Si4416DY N2 1 N-channel MOSFET International Rectifier IRF7805,or Fairchild FDS6670A, or NEC uPA1706, or Hitachi HAT2040R R1 1 20Ω ±5% resistor L1 N1 QUICK-PWM is a trademark of Maxim Integrated Products. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 For small orders, phone 1-800-835-8769. Evaluates: MAX1710/MAX1711 General Description Evaluates: MAX1710/MAX1711 MAX1710 Evaluation Kit Component List (continued) R2, R3, R9 3 1MΩ ±5% resistors R4 1 100kΩ, ±5% resistor R6 0 Not installed R7 1 3Ω, ±5% resistor • 7V to 24V, >20W power supply, battery, or notebook AC adapter • DC bias power supply, 5V at 100mA • Dummy load capable of sinking 7A • Digital multimeter (DMM) R10, R12 1 1kΩ, ±5% resistor • 100MHz dual-trace oscilloscope DESIGNATION QTY DESCRIPTION Quick Start U1 1 MAX1710EEG (24-QSOP) JU1, JU2 2 2-pin headers None 1 Shunt (JU1) SW1 1 DIP-8 dip switch Digi-Key CT2084-ND SW2 1 Momentary switch, normally open Digi-Key P8006/7S J1 1 Scope-probe connector Berg Electronics 33JR135-1 None 1 MAX1710 PC board None 1 MAX1710/MAX1711 data sheet Component Suppliers SUPPLIER 2 Equipment Needed PHONE FAX Central Semiconductor 516-435-1110 516-435-1824 Coilcraft 708-639-6400 708-639-1469 Coiltronics 561-241-7876 561-241-9339 Dale-Vishay 402-564-3131 402-563-6418 Fairchild 408-721-2181 408-721-1635 Hitachi 888-777-0384 650-244-7947 International Rectifier 310-322-3331 310-322-3332 IRC 512-992-7900 512-992-3377 Kemet 408-986-0424 408-986-1442 Motorola 602-303-5454 602-994-6430 NEC 408-588-6000 408-588-6130 Nihon 847-843-7500 847-843-2798 Panasonic 714-373-7939 714-373-7183 Sanyo 619-661-6835 619-661-1055 SGS-Thomson 617-259-0300 617-259-9442 Siliconix 408-988-8000 408-970-3950 Sumida 708-956-0666 708-956-0702 Taiyo Yuden 408-573-4150 408-573-4159 TDK 847-390-4373 847-390-4428 Tokin 408-432-8020 408-434-0375 1) Ensure that the circuit is connected correctly to the supplies and dummy load prior to applying any power. 2) Ensure that the shunt is connected at JU1 (SHDN = VCC). 3) Turn on battery power prior to +5V bias power; otherwise, the output UVLO timer will time out and the fault latch will be set, disabling the regulator until +5V power is cycled or shutdown is toggled. 4) Observe the output with the DMM and/or oscilloscope. Look at the LX switching-node and MOSFET gate-drive signals while varying the load current. 5) Don’t change the DAC code without cycling +5V bias power; otherwise, the output voltage ramp will probably bump into the over- or undervoltage protection thresholds and latch the circuit off. If this happens, just cycle power or press the RESET button. 6) Set switch SW1 per Table 1 to get the desired output voltage. Detailed Description This 7A buck-regulator design is optimized for a 300kHz frequency and output voltage settings around 1.6V. At lower output voltages, transient response is degraded slightly and efficiency worsens. At higher output voltages (approaching 2V), output ripple and reflected input ripple increase. The PC board layout deliberately includes long output power and ground buses in order to facilitate evaluation of the remote sense circuitry and to provide plenty of experimentation space for soldering in different types of output filter capacitors. These buses are also useful for introducing the small amounts of parasitic trace resistance necessary when using capacitors having highfrequency ESR zeros (see the All-Ceramic-Capacitor Application section in MAX1710/MAX1711 data sheet). Position the experimental ceramic capacitors at different places along the length of the buses to see the effect of different amounts of ESR. _______________________________________________________________________________________ MAX1710 Evaluation Kit D3 D2 D1 D0 OUTPUT VOLTAGE (V) 0 0 0 0 2.00 0 0 0 1 1.95 0 0 1 0 1.90 0 0 1 1 1.85 0 1 0 0 1.80 0 1 0 1 1.75 0 1 1 0 1.70 0 1 1 1 1.65 1 0 0 0 1.60 1 0 0 1 1.55 1 0 1 0 1.50 1 0 1 1 1.45 1 1 0 0 1.40 1 1 0 1 1.35 1 1 1 0 1.30 1 1 1 1 1.25 Setting the Output Voltage Select the output voltage using the D0–D3 pins. The MAX1710/MAX1711 uses an internal DAC as a feedback resistor voltage-divider. The output voltage can be digitally set from 1.25V to 2V, in 50mV increments, using the D0–D3 inputs. Switch SW1 sets the desired output voltage (Table 1). Load-Transient Measurement One interesting experiment is to subject the output to large, fast load transients and observe the output with an oscilloscope. This necessitates careful instrumentation of the output, using the supplied scope-probe jack. Accurate measurement of output ripple and load-transient response invariably requires that ground clip leads be completely avoided and that the probe hat be removed to expose the GND shield, so the probe can be plugged directly into the jack. Otherwise, EMI and noise pickup will corrupt the waveforms. Most benchtop electronic loads intended for power-supply testing lack the ability to subject the DC-DC converter to ultra-fast load transients. Emulating the supply current ∆i/∆t at the CPU VCORE pins requires at least 10A/µs load transients. One easy method for generating such an abusive load transient is to solder a MOSFET, such as an MTD3055 or 12N05, directly across the scope-probe jack then drive its gate with a strong pulse generator at a low duty cycle (10%) to minimize heat stress in the MOSFET. Vary the high-level output voltage of the pulse generator to vary the load current. To determine the load current, you might expect to insert a meter in the load path, but this method is prohibited here by the need for low resistance and inductance in the path of the dummy-load MOSFET. There are two easy alternative methods to determine how much load current a particular pulse-generator amplitude is causing. The first and best is to observe the inductor current with a calibrated AC current probe, such as a Tektronix AM503. In the buck topology, the load current is equal to the average value of the inductor current. The second method is to first put on a static dummy load and measure the battery current. Then, connect the MOSFET dummy load at 100% duty momentarily, and adjust the DC gate-drive signal amplitude until the battery current rises to the appropriate level (the MOSFET load must be well heatsinked for this to work without causing smoke and flames). Efficiency Measurements Testing the power conversion efficiency POUT/PIN fairly and accurately requires more careful instrumentation than might be expected. One common error is to use inaccurate DMMs. Another is to use only one DMM, and move it from one spot to another to measure the various input/output voltages and currents. This second error usually results in changing the exact conditions applied to the circuit due to series resistance in the ammeters. It’s best to get four 3-1/2 digit or better DMMs that have been recently calibrated, and monitor VBATT, VOUT, IBATT, and ILOAD simultaneously, using separate test leads directly connected to the input and output PC board terminals. Note that it’s inaccurate to test efficiency at the remote VOUT and ground terminals, as this incorporates the parasitic resistance of the PC board output and ground buses in the measurement (a significant power loss). Remember to include the power consumed by the +5V bias supply when making efficiency calculations: Efficiency = VOUT × I LOAD (VBATT × I BATT ) + (5V × I BIAS ) The choice of MOSFET has a large impact on efficiency performance. The International Rectifier MOSFETs used were of leading-edge performance for the 7A application at the time this kit was designed. However, the pace of MOSFET improvement is rapid, so the latest offerings should be evaluated. _______________________________________________________________________________________ 3 Evaluates: MAX1710/MAX1711 Table 1. MAX1710/1711 Output Voltage Adjustment Settings Evaluates: MAX1710/MAX1711 MAX1710 Evaluation Kit Jumper and Switch Settings Table 2. Jumper JU1 Functions (Shutdown Mode) Table 5. Jumper JU6 Functions (Fixed/Adj. Current-Limit Selection) SHUNT LOCATION SHDN PIN MAX1710 OUTPUT On Connected to VCC MAX1710 enabled Off Connected to GND Shutdown mode, VOUT = 0 CURRENT-LIMIT THRESHOLD ILIM PIN On Connected to VCC 100mV (default) Off Connected to GND via external resistor R6. Refer to Adjustable the ILIM line in the Pin between 50mV Description (MAX1710/ and 200mV MAX1711 data sheet) for information on selecting R6. Table 6. Jumpers JU7/JU10 Functions (GNDS Integrator Disable Selection) Table 3. Jumper JU2 Functions (Low-Noise Mode) SHUNT LOCATION SKIP PIN OPERATIONAL MODE On Connected to VCC Low-noise mode, forced fixedfrequency PWM operation. Connected to GND Normal operation, allows automatic PWM/PFM switchover for pulse skipping at light load, resulting in highest efficiency. Off SHUNT LOCATION JUMPER SHUNT LOCATION GND PIN GROUND REMOTE-SENSE JU7 JU10 On Off Connected to VCC Disables the GNDS integrator Off On Connected to GND directly at the load GNDS internally connects to the integrator that fine-tunes the ground offset voltage. JU7 JU10 Table 7. Jumpers JU8/JU9 Functions (FBS and FB Integrator Disable Selection) Table 4. Jumpers JU3/JU4/JU5 Functions (Switching-Frequency Selection) JUMPER SHUNT LOCATION TON PIN FREQUENCY (kHz) JU3 JU4 and JU5 On Off Connected to VCC 200 JU4 JU3 and JU5 On Off Connected to REF 400 JU5 JU3 and JU4 On Off Connected to GND 550 JU3, JU4, JU5 Off Floating 300 IMPORTANT: Don’t change the operating frequency without first re-calculating component values, because the frequency has a significant effect on the peak current-limit level, MOSFET heating, PFM/PWM switchover point, output noise, efficiency, and other critical parameters. 4 JUMPER SHUNT LOCATION FBS PIN GROUND REMOTE-SENSE JU8 JU9 On Off Connected to VCC Disables the FBS and the main FBREF integrators Off On Connected to VOUT directly at the load FBS internally connects to the integrator that fine-tunes the DC output voltage. JU8 JU9 Table 8. Jumper JU11 Functions (Overvoltage Protection Disable) SHUNT LOCATION OVP PIN OVERVOLTAGE PROTECTION On Connected to VCC OVP disabled Off Connected to GND Normal operation, OVP is enabled. _______________________________________________________________________________________ MAX1710 Evaluation Kit SYMPTOM Circuit won’t start when power is applied. Circuit won’t start when RESET is pressed, +5V bias supply cycled. POSSIBLE PROBLEM SOLUTION Power-supply sequencing: +5V bias supply was applied first. Press the RESET button. Output overvoltage due to shorted high-side MOSFET. Replace the MOSFET. Output overvoltage due to load recovery overshoot Reduce the inductor value, raise the switching frequency, or add more output capacitance. Overload condition Remove the excessive load or raise the ILIM threshold by changing RLIM (R6). Transient overload condition Add more low-ESR output capacitors. Troubleshoot the power stage. Are the DH and DL gate-drive signals present? Is the 2V VREF preBroken connection, bad MOSFET, sent? Exercising OVP mode and then SKIP or other catastrophic problem. no-fault mode can help you decipher the nature of the problem (see MAX1710/MAX1711 data sheet Pin Description). VBATT power source has poor impedance characteristic. Add a bulk electrolytic bypass capacitor across the benchtop power supply, or substitute a real battery. Noise is being injected into FB. Add an RC filter on FB (1kΩ and 100pF suggested) at R11 and C18. FB is crossing the +12.5% OVP threshold or the -70% UVLO threshold due to fast DAC response. This is a normal operating condition. If desired, disable the OVP fault circuit via the OVP input (JU11) or raise the OVP threshold to >2V by substituting a MAX1711 for the MAX1710. On-time pulses are erratic or have unexpected changes in period. Circuit latches off when DAC code is changed. Add parasitic PC board trace resistance between Load-transient waveform shows excess Instability due to low-ESR ceramic the LX-FB connection and the ceramic capacitor. ringing OR LX switching waveform exhibits placed across fast OR double-pulsing (pulses separated only feedback path (FB-GND). Substitute a different capacitor type (OS-CON, tanby a 500ns min off-time). talum, aluminum electrolytic work well). Excessive EMI, poor efficiency at high input voltages. Gate-drain capacitance of N2 is causing shoot-through crossconduction. Observe the gate-source voltage of N2 during the low-to-high LX node transition (this requires careful instrumentation). Is the gate voltage being pulled above 1.5V, causing N2 to turn on? Use a smaller low-side MOSFET or add a higher-value BST resistor (R7). Poor efficiency at high input voltages, N1 gets hot. N1 has excessive gate capacitance. Use a smaller high-side MOSFET or add more heatsinking. _______________________________________________________________________________________ 5 Evaluates: MAX1710/MAX1711 Table 9. Troubleshooting Guide 6 Figure 1. MAX1710 EV Kit Schematic _______________________________________________________________________________________ JU6 17 18 19 20 JU5 550kHz FLOAT = 300kHz 6 8 9 R8 SHORT 5 5 6 7 8 C12 0.22µF R6 OPEN JU4 400kHz R2 1M JU2 21 2 VCC VCC R10 1k JU1 C14 470pF SW1D 4 SW1C 3 SW1B 2 SW1A 1 R3 1M RESET SW2 JU3 VCC 200kHz REF 2V D3 D2 D1 D0 SKIP SHDN GND VBATT 7V TO 24V 7 ILIM TON REF CC D3 D2 D1 D0 SKIP U1 R1 20Ω GND 10 MAX1710 SHDN VCC C11 0.22µF VCC GNDS FBS OVP FB PGND DL LX DH BST V+ PGOOD VDD 15 VDD 12 11 4 16 3 14 13 23 24 22 1 R4 100k JU7 R12 JU8 1k R9 1M C18 OPEN R7 3Ω D2 CMPSH-3 C2 10µF 25V C1 10µF 25V C15 1µF VCC VCC VCC JU10 JU9 J11 R11 SHORT C9 0.1µF VDD C4 10µF 25V C3 10µF 25V PGOOD GNDS FBS VCC N2 N1 D1 L1 2µH C6 470µF 6.3V C7 470µF 6.3V D3 MBRS130LT3 OVP C5 470µF 6.3V C8 10µF 6.3V D4 CMPD2838 3 1 C16 OPEN +5V VBIAS C17 OPEN VOUT J1 SCOPE JACK Evaluates: MAX1710/MAX1711 MAX1710 Evaluation Kit MAX1710 Evaluation Kit Figure 2. Component Placement Guide —Component Side 1.0" Figure 4. Component Placement Guide—Solder Side Evaluates: MAX1710/MAX1711 1.0" 1.0" 1.0" Figure 3. PC Board Layout—Internal GND Plane Layer 2 1.0" Figure 5. PC Board Layout—Component Side _______________________________________________________________________________________ 7 Evaluates: MAX1710/MAX1711 MAX1710 Evaluation Kit 1.0" 1.0" Figure 6. PC Board Layout—Internal GND Plane Layer 3 Figure 7. PC Board Layout—Solder Side Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.