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19-1647; Rev 1; 6/00
MAX1711 Voltage Positioning Evaluation Kit
General Description
The MAX1711 evaluation kit (EV kit) demonstrates the high-power, dynamically adjustable notebook CPU application circuit with voltage positioning. Voltage positioning decreases CPU power consumption and reduces output capacitance requirements. This DC-DC converter steps down high-voltage batteries and/or AC adapters, generating a precision, low-voltage CPU core VCC rail. The MAX1711 EV kit provides a digitally adjustable 0.925V to 2V output voltage from a 7V to 24V battery input range. It delivers sustained output current of 12A and 14.1A peaks, operating at a 550kHz switching frequency, and has superior line- and load-transient response. The MAX1711 EV kit is designed to accomplish output voltage transitions in a controlled amount of time with limited input surge current. This EV kit is a fully assembled and tested circuit board. o Output Voltage Positioned o Reduces CPU Power Consumption o Lowest Number of Output Capacitors (only 4) o High Speed, Accuracy, and Efficiency o Fast-Response Quick-PWMTM Architecture o 7V to 24V Input Voltage Range o 0.925V to 2V Output Voltage Range o 12A Load-Current Capability (14.1A peak) o 550kHz Switching Frequency o Power-Good Output o 24-Pin QSOP Package o Low-Profile Components o Fully Assembled and Tested
Features
Evaluates: MAX1711
Ordering Information
PART MAX1711EVKIT TEMP. RANGE 0C to +70C IC PACKAGE 24 QSOP
Quick-PWM is a trademark of Maxim Integrated Products.
Component List
DESIGNATION QTY DESCRIPTION 10F, 25V ceramic capacitors Taiyo Yuden TMK432BJ106KM, Tokin C34Y5U1E106Z, or United Chemi-Con/Marcon THCR50E1E106ZT 220F, 2.5V, 25m low-ESR polymer capacitors Panasonic EEFUEOE 221R 10F, 6.3V ceramic capacitor Taiyo Yuden JMK325BJ106MN or TDK C3225X5R1A106M 0.1F ceramic capacitor 0.01F ceramic capacitor (not installed) 0.22F ceramic capacitors 0.1F ceramic capacitor (not installed) 470pF ceramic capacitor 1F ceramic capacitor 1000pF ceramic capacitor 2A Schottky diode SGS-Thomson STPS2L25U or Nihon EC31QS03L N2, N3 2 N1 1 DESIGNATION QTY D2 1 DESCRIPTION 100mA Schottky diode Central Semiconductor CMPSH-3 1A Schottky diode Motorola MBRS130LT3, International Rectifier 10BQ040, or Nihon EC10QS03 200mA switching diode Central Semiconductor CMPD2838 Scope-probe connector Berg Electronics 33JR135-1 2-pin header Not installed 0.47H power inductor Sumida CEP 125 series 4712-T006 N-channel MOSFET (SO-8) International Rectifier IRF7811 or IRF7811A N-channel MOSFET (SO-8) International Rectifier IRF7805 or IRF7811 or IRF 7811A
C1-C4, C20
5
D3
1
C5, C6, C7, C16
4
D4 J1 JU1 JU3-9 L1
1 1 1 0 1
C8 C9 C10 C11, C12 C13 C14 C15 C18 D1
1 1 0 2 0 1 1 1 1
________________________________________________________________ Maxim Integrated Products
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MAX1711 Voltage Positioning Evaluation Kit Evaluates: MAX1711
Component List (continued)
DESIGNATION QTY N4, N5 (not installed) R1 R2 R3 R4 R6 R9 R10 R11 R12 R13 R14 SW1 SW2 U1 U2 (not installed) None None None 0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 DESCRIPTION N-channel MOSFETs Motorola 2N7002 or Central Semiconductor 2N7002 20 5% resistor Not installed 1M 5% resistor 100k 5% resistor 100k 1% resistor 140k 1% resistor 1k 5% resistor 100 5% resistor 0.005 1%, 1W resistor Dale WSL-2512-R005F 1M 1% resistor 10k 1% resistor DIP-10 dip switch Momentary switch, normally open Digi-Key P8006/7S MAX1711EEG (24-pin QSOP) Exclusive-OR gate (5-Pin SSOP) Toshiba TC4S30F Shunt (JU1) MAX1711 PC board MAX1711 data sheet SUPPLIER Central Semiconductor Dale-Vishay Fairchild International Rectifier Kemet Motorola Nihon Panasonic Sanyo SGS-Thomson Sumida Taiyo Yuden TDK Tokin
Component Suppliers
PHONE 516-435-1110 402-564-3131 408-721-2181 310-322-3331 408-986-0424 602-303-5454 847-843-7500 714-373-7939 619-661-6835 617-259-0300 708-956-0666 408-573-4150 847-390-4373 408-432-8020 FAX 516-435-1824 402-563-6418 408-721-1635 310-322-3332 408-986-1442 602-994-6430 847-843-2798 714-373-7183 619-661-1055 617-259-9442 708-956-0702 408-573-4159 847-390-4428 408-434-0375
Note: Please indicate that you are using the MAX1711 when contacting these component suppliers.
5) 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 (press the RESET button). 6) 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.
Recommended Equipment
* 7V to 24V, >20W power supply, battery, or notebook AC adapter * DC bias power supply, 5V at 100mA * Dummy load capable of sinking 14.1A * Digital multimeter (DMM) * 100MHz dual-trace oscilloscope
Detailed Description
This 14A buck-regulator design is optimized for a 550kHz frequency and output voltage settings around 1.6V. At VOUT = 1.6V, inductor ripple is approximately 35%, with a resulting pulse-skipping threshold at roughly ILOAD = 2.2A.
Quick Start
1) Ensure that the circuit is connected correctly to the supplies and dummy load prior to applying power. 2) Ensure that the shunt is connected at JU1 (SHDN = VCC). 3) Set switch SW1 per Table 1 to achieve the desired output voltage. 4) Connect +5V or ground to the AC Present pad to disable the transition detector circuit. See the Dynamic Output Voltage Transitions section for more information regarding the transition detector circuit.
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Setting the Output Voltage
Select the output voltage using the D0-D4 pins. The MAX1711 uses an internal 5-bit DAC as a feedback resistor voltage divider. The output voltage can be digitally set from 0.925V to 2V using the D0-D4 inputs. Switch SW1 sets the desired output voltage. See Table 1.
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MAX1711 Voltage Positioning Evaluation Kit
Table 1. MAX1710/1711 Output Voltage Adjustment Settings
D4 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 D3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 D2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 D1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 D0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 OUTPUT VOLTAGE (V) 2.00 1.95 1.90 1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50 1.45 1.40 1.35 1.30 Shutdown 1.275 1.250 1.225 1.200 1.175 1.150 1.125 1.100 1.075 1.050 1.025 1.000 0.975 0.950 0.925 Shutdown
tial output voltage 20mV high, and R12 (5m) causes the output voltage to drop with increasing load (60mV or about 4% of 1.6V at 12A). Setting the output voltage high allows a larger stepdown when the output current increases suddenly, and regulating at the lower output voltage under load allows a larger step-up when the output current suddenly decreases. Allowing a larger step size means that the output capacitance can be reduced and the capacitor's ESR can be increased. If voltage positioning is not used, one additional output capacitor is required to meet the same transient specification. Reduced power consumption at high load currents is an additional benefit of voltage positioning. Because the output voltage is reduced under load, the CPU draws less current. This results in lower power dissipation in the CPU, though some extra power is dissipated in R12. For a 1.6V, 12A nominal output, reducing the output voltage 2.75% (1.25% - 4%) gives an output voltage of 1.556V and an output current of 11.67A. So the CPU power consumption is reduced from 19.2W to 18.16W. The additional power consumption of R12 is 5m * 11.7A2 = 0.68W, and the overall power savings is 19.2 - (18.16 + 0.68) = 0.36W. In effect, 1W of CPU dissipation is saved and the power supply dissipates much of the savings, but both the net savings and the transfer of dissipation away from the hot CPU are beneficial.
Evaluates: MAX1711
Dynamic Output Voltage Transitions
If the DAC inputs (D0-D4) are changed, the output voltage will change accordingly. However, under some circumstances, the output voltage transition may be slower than desired. All transitions to a higher voltage will occur very quickly, with the circuit operating at the current limit set by the voltage at the ILIM pin. Transitions to a lower output voltage require the circuit or the load to sink current. If SKIP is held low (PFM mode), the circuit won't sink current, so the output voltage will decrease only at the rate determined by the load current. This is often acceptable, but some applications require output voltage transitions to be completed within a set time limit. Powering CPUs with Intel's Geyserville technology is such an application. The specification requires that output voltage transitions occur within 100s after a DAC code change. This fast transition timing means that the regulator circuit must sink as well as source current. The simplest way of meeting this requirement is to use the MAX1711's fixed-frequency PWM mode (set SKIP high), allowing the regulator to sink or source currents equally. This EV kit is shipped with SKIP set high. Although this results in a V DD quiescent current to 20mA or more, depending on the MOSFETs and
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Voltage Positioning
The MAX1711 EV kit uses voltage positioning to minimize the output capacitor requirements of the Intel Coppermine CPU's transient voltage specification (-7.5% to +7.5%). The output voltage is initially set slightly high (1.25%) and then allowed to regulate lower as the load current increases. R13 and R14 set the ini-
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MAX1711 Voltage Positioning Evaluation Kit Evaluates: MAX1711
switching frequency used, it is often an acceptable choice. A similar but more clever approach is to use PWM mode only during transitions. This approach allows the regulator to sink current when needed and to operate with low quiescent current the rest of the time, but it requires that the system know when the transitions will occur. Any system with a changing output voltage must know when its output voltage changes occur. Usually, it is the system that initiates the transition, either by driving the DAC inputs to new levels or by selecting new DAC inputs with a digital mux. While it is possible for the regulator to recognize transitions by watching for DAC code changes, the glue logic needed to add that feature to existing controllers is unnecessarily complicated (refer to the MAX1710/MAX1711 data sheet, Figure 10). It is easier to use the chipset signal that selects DAC codes at the mux, or some other system signal to inform the regulator that a code change is occurring. For easy modification, the MAX1711 EV kit is designed to use an external chipset signal to indicate DAC code transitions (install U2, R2, C10, C13; short JU9 and cut JU10). This signal connects to the EV kit's AC Present pad and should have 5V logic levels. Logic edges on AC Present are detected by exclusive-OR gate U2, which generates a 60s pulse on each edge (determined by R2 and C10). These pulses drive SKIP, allowing the regulator to sink current during transitions. Because U2 is powered by VCC (5V), the signal connected to AC Present must have 5V logic levels so that U2's output pulses will be symmetric for positive- and negative-going transitions. If the signal that's available to drive AC Present has a different logic level, either level-shift the signal or lift U2's supply pin and power it from the appropriate supply rail. In addition to controlling SKIP, the pulses from U2 have two other functions, which are optional. U2's output drives the gates of two small-signal MOSFETs, N4 and N5 (not installed). N4 is used to temporarily reduce the circuit's current limit, in effect soft-starting the regulator. This reduces the battery surge current, which otherwise would discharge (upward transitions) or charge (downward transitions) the regulator input (battery) at a rate determined by the regulator's maximum current limit. N5 pulls down on PGOOD during transitions, indicating that the output voltage is in transition. 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 powersupply testing are unable to subject the DC-DC converter to ultra-fast load transients. Emulating the supply current di/dt at the CPU VCORE pins requires at least 10A/s load transients. One easy method for generating such an abusive load transient is to solder a MOSFET, such as an MTP3055 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 adjust 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 for determining 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 gate-drive signal 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 and Effective Efficiency
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 termi-
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.
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MAX1711 Voltage Positioning Evaluation Kit
nals, because doing 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 x I LOAD (VBATT x I BATT ) + (5V x I BIAS ) cy is the efficiency required of a nonvoltage-positioned circuit to equal the total dissipation of a voltage-positioned circuit for a given CPU operating condition. Calculate effective efficiency as follows: * Start with the efficiency data for the positioned circuit (VIN, IIN, VOUT, IOUT). * Model the load resistance for each data point (RLOAD = VOUT / IOUT). * Calculate the output current that would exist for each RLOAD data point in a nonpositioned application (INP = VNP / RLOAD, where VNP = 1.6V in this example). * Effective efficiency = (VNP INP) / (VIN IIN) = calculated nonpositioned power output divided by the measured voltage-positioned power input. * Plot the efficiency data point at the current INP. The effective efficiency of the voltage-positioned circuit will be less than that of the nonpositioned circuit at light loads where the voltage-positioned output voltage is higher than the nonpositioned output voltage. It will be greater than that of the nonpositioned circuit at heavy loads where the voltage-positioned output voltage is lower than the nonpositioned output voltage.
Evaluates: MAX1711
The choice of MOSFET has a large impact on efficiency performance. The International Rectifier MOSFETs used were of leading-edge performance for the 12A application at the time this kit was designed. However, the pace of MOSFET improvement is rapid, so the latest offerings should be evaluated. Once the actual efficiency data has been obtained, some work remains before an accurate assessment of a voltage-positioned circuit can be made. As discussed in the Voltage Positioning section, a voltagepositioned power supply can dissipate additional power while reducing system power consumption. For this reason, we use the concept of effective efficiency, which allows the direct comparison of a positioned and nonpositioned circuit's efficiency. Effective efficien-
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MAX1711 Voltage Positioning Evaluation Kit Evaluates: MAX1711
Jumper and Switch Settings
Table 2. Jumper JU1 Functions (Shutdown Mode)
SHUNT LOCATION Installed Not Installed SHDN PIN Connected to VCC Connected to GND MAX1711 OUTPUT MAX1711 enabled Shutdown mode, VOUT = 0
Table 4. Jumper JU6 Functions (Fixed/Adjustable Current-Limit Selection)
SHUNT LOCATION Installed ILIM PIN Connected to VCC CURRENT-LIMIT THRESHOLD 100mV
Not Installed
Table 3. Jumpers JU3/JU4/JU5 Functions (Switching-Frequency Selection)
SHUNT LOCATION JU3 Installed Not Installed Not Installed Not Installed JU4 Not Installed Installed Not Installed Not Installed JU5 Not Installed Not Installed Installed Not Installed TON PIN Connected to VCC Connected to REF Connected to GND Floating FREQUENCY (kHz) 200 400 550 300
Connected to GND via an external resistor divider, Adjustable R6/R9. Refer to the Pin between 50mV Description ILIM section in and 200mV the MAX1711 data sheet for more information.
Table 5. Jumpers JU9/JU10 Functions (FBS and FB Integrator Disable Selection)
SHUNT LOCATION JU9 Installed Not Installed JU10 Not Installed Installed SKIP PIN Connected to VCC Connected to the output of U2
IMPORTANT: Don't change the operating frequency without first recalculating component values because the frequency has a significant effect on the peak current-limit level, MOSFET heating, preferred inductor value, PFM/PWM switchover point, output noise, efficiency, and other critical parameters.
Table 6. Troubleshooting Guide
SYMPTOM Circuit won't start when power is applied. POSSIBLE PROBLEM Power-supply sequencing: +5V bias supply was applied first. Output overvoltage due to shorted high-side MOSFET. Output overvoltage due to load Circuit won't start when RESET is pressed, recovery overshoot. +5V bias supply cycled. Overload condition. SOLUTION Press the RESET button. Replace the MOSFET. Reduce the inductor value, raise the switching frequency, or add more output capacitance. Remove the excessive load.
Troubleshoot the power stage. Are the DH and DL Broken connection, bad MOSFET, gate-drive signals present? Is the 2V VREF preor other catastrophic problem. sent? On-time pulses are erratic or have unexpected changes in period. VBATT power source has poor impedance characteristic. Add a bulk electrolytic bypass capacitor across the benchtop power supply, or substitute a real battery.
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7V TO 24V
VBATT VCC VDD VCC C11 R1 0.22F 20 C21 OPEN 7 15 VDD V+ R7 SHORT D2 CMPSH-3 C15 1F +5V VBIAS 1 2 SHDN VCC VDD R10 1k C1 10F 25V C2 10F 25V C3 10F 25V C4 10F 25V C20 10F 25V
GND
RESET JU1
SW2
SHDN
R3 1M 21 SKIP 7 8 20 D0 DH 3 L1 0.47H 6 7 6 5 D1 N3 1 2 C5 220F 2.5V 8 4 5 N2 1 2 C9 0.1F D1 LX 7 18 D2 8 DL 17 D3 PGND 16 D4 FB C18 1000pF 3 R8 SHORT 5 CC R11 100 14 7 8 23 24 4 10 19 9 R12 0.005 1% D3 C6 220F 2.5V C7 220F 2.5V BST 22
SKIP
SKIP
D0
D4 CMPD2838
J1 SCOPE JACK
1
6 5 N1 1 2
SW1A
VOUT
Figure 1. MAX1711 Voltage Positioning EV Kit Schematic
C8 10F 6.3V
D1
2
SW1B
D2
3
U1 MAX1711
13 4
SW1C
D3
4
C16 220F 2.5V
C17 OPEN
C19 OPEN
SW1D
D4
C14 470pF
5 9 REF FBS 11 8 TON R14 10k 1% 12 AGND 10 R4 100k PGOOD VCC PGOOD GNDS R13 1M 1% REF 4
6
SW1E
C12 0.22F
REF 2V FLOAT = 300kHz
JU4 400kHz
VCC JU5 550kHz 6 ILIM
JU3 200kHz
JU6
MAX1711 Voltage Positioning Evaluation Kit
Evaluates: MAX1711
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ILIM PGOOD
7
MAX1711 Voltage Positioning Evaluation Kit Evaluates: MAX1711
PGOOD
JU10 SHORT (PC TRACE) VCC 2 C13 0.1F
3
1
N5
NOT INSTALLED
JU9 N4 VCC 5 U2 2 4 1 TC4S30F R2 10k ILIM C10 0.01F 3 1 R6 100k 1% 3 R9 140k 1% 2
Figure 1. MAX1711 Voltage Positioning EV Kit Schematic (continued) 8 _______________________________________________________________________________________
AC PRESENT
SKIP
MAX1711 Voltage Positioning Evaluation Kit Evaluates: MAX1711
1.0"
1.0"
Figure 2. MAX1711 Voltage Positioning EV Kit Component Placement Guide--Component Side
Figure 3. MAX1711 Voltage Positioning EV Kit Component Placement Guide--Solder Side
1.0"
1.0"
Figure 4. MAX1711 Voltage Positioning EV Kit PC Board Layout--Component Side
Figure 5. MAX1711 Voltage Positioning EV Kit PC Board Layout--Internal GND Plane (Layer 2) 9
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MAX1711 Voltage Positioning Evaluation Kit Evaluates: MAX1711
1.0"
1.0"
Figure 6. MAX1711 Voltage Positioning EV Kit PC Board Layout--Internal GND Plane (Layer 3)
Figure 7. MAX1711 Voltage Positioning EV Kit 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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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