IRNBPS1

PD-91748 IRNBPS1 TM Mobile Pentium II Power Supply Evaluation Board 90% Peak Efficiency Achieved The new IRNBPS1 evaluation board offers the power supply designer a convenient way to evaluate power MOSFET performance in DC/DC converters powering next-generation mobile processors. A synchronous buck regulator topology operating at 300 kHz is employed. A DAC selectable output voltage allows evaluation at various voltages for existing and forthcoming mobile processors. The new 30V low threshold SO-8 IRF7805 and IRF7807 HEXFET© MOSFETs, specifically designed for the application, are used to improve circuit efficiency through reduced RDS(on) and gate charge. The IRF7805 and IRF7807 are optimized for switching and conduction losses under the operating range. A detailed schematic along with complete efficiency and thermal performance characterization are offered to reduce the customer’s test and verification time when designing with IR MOSFETs. Purpose This evaluation tool is available to power supply designers to verify and qualify the performance of IR power MOSFETs under “real world” mobile CPU DC/ DC converter conditions. Web Site This evaluation board datasheet as well as the IRF7805 and IRF7807 datasheets may be downloaded at IR’s web site (http://www.irf.com). Datasheets are in PDF format for on screen viewing or printing. Evaluation Boards Evaluation boards are available through your local IR sales office in the Mobile Pentium II Design Kit order as IRNBPS1. Fig 1. IRNBPS1 Key Features • 90% Peak Efficiency @ 10Vin • Designed for new mobile Pentium II processors. • Accepts input voltages from 10V to 24V • 1.25 to 2.00V digitally selectable output • Up to 7A continuous output • Complete efficiency characterization • Complete thermal characterization • Design kit available: IRNBPS1 TM TM Support E-mail Chris Davis at cdavis1@irf.com for support of this evaluation board and the IRF7805 and IRF7807 MOSFETs. © International Rectifier, 1998 Intel Trademark TM International Rectifier IRNBPS1 Specifications Absolute Maximum Ra tings Param eter Input Voltage Digital I/O Continuous Output Current T able 1 Table 2. VID Codes M in -0.3 - M ax 30.0 +6.0 8.5 Units V V A Efficiency, Typical Param eter ηpeak, V out = 1.6V, Fixed PW M η @ I out = 5.6A, Vout = 1.6V, Fixed PW M V in = 10V 90 86.8 V in = 14V 88.5 85.8 V in = 24V 83.5 82 Units % % Electrical Input Specifications Param eter Input Voltage Input Current M in 10 - Typ 14 .64 M ax 24 2.0 Units V A Power O utput Specificatio ns (all specified line and load conditio ns) Param eter Voltage Range Output Current Voltage Regulation M in 1.25 0 - Typ 1.60 5.6 0.20 M ax 2.0 7.0 1 Units V A % Digital Input/O utput Specificatio ns Signal PGD, O N/OFF, DO -D3, SKIP, SYNC Input/Output input Conditions/Description Logic Output Fault Pro tection Param eter Ov er Voltage Ov er Current Under Voltage M in +4 8 60 Circuit Description The IRNBPS1 evaluation board provides a digitally adjustable output voltage between 1.25V and 2V from a 10V to 24 V input supply. The output voltage is digitally adjusted by the MAX5480, a multiplying digital to analog converter (DAC). Refer to Table 2 for the DAC codes. The IRF7805 and IRF7807 HEXFET Power MOSFETs, as well as the MAX1636 control IC are rated for 30V; however, the design kit is restricted to 24V operating range due to the ratings of other components and minimum duty-factor limitations. The power MOSFETs were specifically designed for optimal efficiency at Vin = 14V, Vout = 1.6V, and Iout = 5.6A, with a 10V-24V input voltage swing, and Ioutmax = 7A (typical 4 cell Lithium-Ion operating conditions). All components were chosen for 300kHz switching frequency. The MAX1636 Control IC has an internal linear regulator for supplying its own VCC power from the input voltage of the supply. If a 5 volt bus or supply is available, it is recommended to use the “optional +5V” input, instead of the internal linear regulator. Typ +7 10 70 M ax +10 12 80 Units % A % This will decrease gate drive power losses and increase efficiency. To use this option, disconnect pin 13 from its pad or cut the trace, connect jumper JU6, then connect the +5V supply to either the connector pins A4, A5, B4 or to the +5V test point. Jumper Description Table 3: Jumper JU1 Functions Shunt Location Pin 1, 2 Pin 3, 4 OFF (Recommended) MAX1636 Operating Gain Pin Mode REF 0.5% AC Regulation VCC 1% AC Regulation GND 2% AC Regulation Table 4: Jumper JU2 Functions Shunt Location OFF ON MAX1636 Operating SKIP Pin Mode Idle mode, pulse GND skipping operation, for highest light-load efficiency Low-noise mode, VCC fixed frequency PWM operation. Table 5: Jumper JU3 Functions Shunt Location OFF MAX1636 SYNC Pin VCC Frequency (kHz) 300 ON GND 200 # D 3 D 2 D 1 D 0 Vo u t 0 0 0 0 0 2 .0 1 0 0 0 1 1 .9 5 2 0 0 1 0 1 .9 3 0 0 1 1 1 .8 5 4 0 1 0 0 1 .8 5 0 1 0 1 1 .7 5 6 0 1 1 0 1 .7 7 0 1 1 1 1 .6 5 8 1 0 0 0 1 .6 9 1 0 0 1 1 .5 5 10 1 0 1 0 1 .5 11 1 0 1 1 1 .4 5 12 1 1 0 0 1 .4 13 1 1 0 1 1 .3 5 14 1 1 1 0 1 .3 15 1 1 1 1 1 .2 5 Table 6: Jumper JU4 Functions Shunt Location OFF MAX1636 OVP Pin VCC ON GND Over-Voltage Protection Enabled Disabled Table 7: Jumper JU5 Functions Shunt Location ON OFF MAX1636 SHDN Pin GND VIN MAX1636 Output Shutdown mode, Vout=0V Enabled Latched Fault Protection The MAX1636 contains a latched faultprotection circuit that disables the IC when the output is over-voltage or under-voltage (or when thermal shutdown is triggered). Once disabled, the supply won’t attempt to restart until input power is cycled or until SHDN(JU5) is cycled. A fault condition can be triggered by overloading the output, over-voltaging the output (which can happen when changing the DAC code settings), or by touching sensitive compensation or feedback nodes. 2 Fig 2. IRNBPS1 Schematic Diagram International Rectifier IRNBPS1 3 International Rectifier IRNBPS1 Static Performance Efficiency High efficiency is expected in a mobile CPU converter. Thanks to the application specific IRF7805 & IRF7807 MOSFETs, the efficiency is kept high throughout low load Fig 3. Typical Efficiency, Constant Frequency PWM Vout = 1.6V, fs = 300kHz, +5V ext. to full load at V out = 1.6V (Figure 3). The efficiency also increases if the output Efficiency could be boosted up if the sense voltage is raised to 1.8V, such as for existing resistor was eliminated as in voltage mode CPU voltage rails (Figure 5). schemes (Figure 4). Fig 4. Calculated Efficiency with RSENSE Removed, PWM Vout = 1.6V, fs = 300kHz, +5V ext. Fig 6. Typical T j of Q1 Ta = 25ºC, Vout = 1.6V (still air) Fig 5. Typical Efficiency, Constant Frequency PWM Vout = 1.8V, fs = 300kHz, +5V ext. Fig 7. Typical T j of Q2 Ta = 25ºC, Vout = 1.6V (still air) Maximum Junction Temperature Measurement of Q1 & Q2 junction temperatures shows that they remain low at an ambient temperature of 25°C, even in still air. Operation under 50°C ambient will maintain sufficient margin under the component temperature ratings. WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, Tel: (310) 322 3331 EUROPEAN HEADQUARTERS: Hurst Green, Oxted, Surrey RH8 9BB, UK Tel: ++ 44 1883 732020 IR CANADA: 15 Lincoln Court, Brampton, Ontario L6T 3Z2, Tel: (905) 453 2200 IR GERMANY: Saalburgstrasse 157, 61350 Bad Homburg Tel: ++ 49 6172 96590 IR ITALY: Via Liguria 49, 10071 Borgaro, Torino Tel: ++ 39 11 451 0111 IR FAR EAST: K&H Bldg., 2F, 3-30-4 Nishi-Ikebukuro, Toshima-ku, Tokyo 171 Japan Tel: 81 3 3983 0641 IR SOUTHEAST ASIA: 315 Outram Road, #10-02 Tan Boon Liat Building, Singapore 0316 Tel: 65 221 8371 http://www.irf.com/ Data and specifications subject to change without notice. 4/98