600kHz High Input Voltage,  Step-Down DC/DC Voltage Regulator: SP7656 PowerBlox  <ul><li>Source: EXAR Corporation  </li></ul>
Introduction <ul><li>Purpose </li></ul><ul><ul><li>Study on 600kHz High Input Voltage, Step-Down DC/DC Voltage Regulator. ...
Features  <ul><li>Wide Input Voltage Range 4.5V - 29V.  </li></ul><ul><li>3 Amps Continuous (4A Peak) Output Current.  </l...
Converter Block Diagram
Over-Current Protection  <ul><li>The over-current protection circuit functions by monitoring the voltage across the intern...
SP7656 Loop Compensation  <ul><li>Type-2 internal compensation is sufficient if the following condition is met:  </li></ul...
Design Guidelines <ul><li>Using the ON/OFF Function via VFB : </li></ul><ul><li>The feedback pin serves a dual role of On/...
Input / Output Capacitance Selection <ul><li>Input Capacitance Selection: </li></ul><ul><li>Voltage rating is nominally se...
Typical Performance Curve Efficiency vs. Load   VFB vs. Load   SWN & Output Ripple Voltage
SP7656-Evaluation Board Schematic  SP7656EB Demo Board
Typical Application Circuit
Additional Resource <ul><li>For ordering  SP7656  , please click the part list or </li></ul><ul><li>Call our sales hotline...
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Study on 600kHz High Input Voltage, Step-Down DC/DC Voltage Regulator

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600kHz High Input Voltage, Step-Down DC/DC Voltage Regulator: SP7656 PowerBlox

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  • This is an introduction to the EXAR 600KHZ High Input Voltage Step-Down DC/DC Voltage Regulator SP7656 Power Blox
  • Welcome to the training module on the SP7656 . This training module gives an overview function and operation of the device and application details.
  • The SP7656 is a PWM controlled step down (buck) voltage mode regulator co-packaged with a P-Channel FET. It operates from 4.5V to 29V making it suitable for 5V, 12V and 24V applications. The programmable over-current protection is based on internal FET resistance sensing and allows setting the over-current protection value up to a 300mV threshold.
  • The SP7656 PowerBlox is a fixed frequency, voltage mode, non-synchronous PWM controller co-packaged with a P-Channel FET. SP7656 has Type-2 internal compensation for use with Electrolytic/Tantalum output capacitors. A precision 0.6V reference, present on the positive terminal of the internal error amplifier, permits programming of the output voltage down to 0.6V via the FB pin. The output of the Error Amplifier is internally compared to a feed-forward (VIN/5 peak-to-peak) ramp and generates the PWM control. Timing is governed by an internal oscillator that sets the PWM frequency at 600kHz.
  • The SP7656 contains useful protection features. Over-current protection is based on the internal MOSFET Rds(on) and is programmable via a resistor placed between ISET and LX node. Under-Voltage Lock-Out (UVLO) ensures that the controller starts functioning only when sufficient voltage exists for powering IC’s internal circuitry. The over-current protection circuit functions by monitoring the voltage across the internal P-Channel FET. The FET has nominal Rds(on) of 0.06Ω, assuming no temperature rise.
  • The SP7656 includes Type-2 internal compensation components for loop compensation. External compensation components are not required for systems with tantalum or aluminum electrolytic output capacitors with sufficiently high ESR. The above condition requires the ESR zero to be at a lower frequency than the double-pole from the LC filter. If this condition is not met, Type-3 compensation should be used and can be accomplished by placing a series RC combination in parallel with R1 as shown.
  • This page gives information about programming the output voltage, soft start, and function using the VFB pin.
  • This Page gives information about input and output capacitance selection for the SP7656 device. Voltage rating is nominally selected to be approximately twice the input voltage. Input voltage ripple has three components: ESR and ESL cause a step voltage drop upon turn on of the MOSFET. The Output capacitor is selected for voltage rating, capacitance and Equivalent Series Resistance (ESR).
  • The SP7656ER is designed with an accurate 2.0% reference over line, load and temperature. The graph data shows a typical SP7656 evaluation board efficiency and regulation plots, with efficiencies up to 87% and output currents up to 4A. The output voltage ripple of less than 6.6mV at full load and the LX node are shown. All waveforms were taken under 12V to 3.3V conversion.
  • The SP7656 Evaluation Board design was optimized for 12V down conversion to 3.3V, changes of output voltage and/or input voltage will alter performance from the data given in the Power Supply data section. Connect a Load between the VOUT and GND posts, again using short leads to minimize parasitic inductance and voltage drop. It’s best to GND reference the scope and digital meters using a single GND post in the output of the board. The SP7656 Evaluation Board has been tested and delivered with the output set to 3.3V, by simply changing one resistor, R2, the SP7656 can be set to other output voltages.
  • The SP7656 is optimized to provide superior performance for low duty cycle applications. For applications with output voltages below 9V, the device will operate normally at the expected 600kHz switching frequency for conversions with less than 50% duty cycle. For applications with output voltages below 9V and greater than 50% duty cycle, the device will enter into a pulse skipping mode. This is due to the FB voltage to internal ramp voltage ratio of the device, and is an intended behaviour from an architecture optimized for superior performance in low duty cycle conversion applications and results in a small increase in output ripple voltage for any given circuit.
  • Thank you for taking the time to view this presentation on “SP7656 ” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the EXAR Corporation site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit Element 14 e-community to post your questions.
  • Study on 600kHz High Input Voltage, Step-Down DC/DC Voltage Regulator

    1. 1. 600kHz High Input Voltage, Step-Down DC/DC Voltage Regulator: SP7656 PowerBlox <ul><li>Source: EXAR Corporation </li></ul>
    2. 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>Study on 600kHz High Input Voltage, Step-Down DC/DC Voltage Regulator. </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>Features and device Block Diagram. </li></ul></ul><ul><ul><li>Over-current and Loop compensation. </li></ul></ul><ul><ul><li>Design guidelines, input and output capacitance selection. </li></ul></ul><ul><ul><li>SP7656 Evaluation Board Details. </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>12 pages </li></ul></ul>
    3. 3. Features <ul><li>Wide Input Voltage Range 4.5V - 29V.  </li></ul><ul><li>3 Amps Continuous (4A Peak) Output Current. </li></ul><ul><li>Internal Compensation. </li></ul><ul><li>Input Feed forward Control improves </li></ul><ul><li>Transient and Regulation. </li></ul><ul><li>600kHz Constant Frequency Operation. </li></ul><ul><li>Low 0.6V Reference Voltage. </li></ul><ul><li>High output set point accuracy of 1%. </li></ul><ul><li>Internal Soft Start. </li></ul><ul><li>Small SO8-EP Thermally Enhanced Package. </li></ul><ul><li>Adjustable Overcurrent Protection. </li></ul><ul><li>Lead Free, RoHS Compliant Package. </li></ul>
    4. 4. Converter Block Diagram
    5. 5. Over-Current Protection <ul><li>The over-current protection circuit functions by monitoring the voltage across the internal P-Channel FET. </li></ul><ul><li>When this voltage exceeds 0.3V (nominal), the over-current comparator triggers and the controller enters hiccup mode. </li></ul><ul><li>The maximum value of Rs should be limited to 3kΩ. </li></ul><ul><li>The over-current will trigger at I ocp = 0.3V/0.06Ω=5A . </li></ul>
    6. 6. SP7656 Loop Compensation <ul><li>Type-2 internal compensation is sufficient if the following condition is met: </li></ul>RZ and CZ in conjunction for Type-3 compensation <ul><li>The value of CZ can be calculated as follows and RZ selected from table: </li></ul>RZ Selection Table
    7. 7. Design Guidelines <ul><li>Using the ON/OFF Function via VFB : </li></ul><ul><li>The feedback pin serves a dual role of On/Off control. </li></ul><ul><li>The MOSFET driver is disabled when a voltage greater than 1V is applied at FB pin. Maximum voltage rating of this pin is 5.5V. </li></ul><ul><li>The controlling signal should be applied through a small signal diode to FB pin . </li></ul><ul><li>Programming the Output Voltage: </li></ul><ul><li>Output voltage is calculated using the following equation: </li></ul><ul><ul><li>0.6 is used as it is the reference voltage of the SP7656. </li></ul></ul><ul><ul><li>200k is a fixed-value and is the top resistor in the output set point resistor pair. R1 of the output voltage divider should always be 200kΩ. </li></ul></ul><ul><li>Soft Start : </li></ul><ul><li>Soft Start is preset internally to 5ms (nominal). Internal Soft Start eliminates the need for the external capacitor CSS that is commonly used to program this function . </li></ul>
    8. 8. Input / Output Capacitance Selection <ul><li>Input Capacitance Selection: </li></ul><ul><li>Voltage rating is nominally selected to be </li></ul><ul><li>approximately twice the input voltage. </li></ul><ul><li>Total input voltage ripple should be maintained </li></ul><ul><li>below 1.5% of VIN. </li></ul><ul><li>Input voltage ripple has three components: </li></ul><ul><li>ESR and ESL cause a step voltage drop </li></ul><ul><li>upon turn on of the MOSFET. </li></ul><ul><li>Output Capacitor Selection : </li></ul><ul><li>Output capacitor is selected for voltage rating, capacitance and Equivalent Series Resistance (ESR). </li></ul><ul><li>A steady-state output current IOUT corresponds </li></ul><ul><li>to inductor stored energy of ½ L IOUT2. </li></ul><ul><li>A sudden decrease in IOUT forces the energy surplus in L to be absorbed by COUT. This causes an overshoot in output voltage that is corrected by the power switch reducing in duty cycle. </li></ul>
    9. 9. Typical Performance Curve Efficiency vs. Load VFB vs. Load SWN & Output Ripple Voltage
    10. 10. SP7656-Evaluation Board Schematic SP7656EB Demo Board
    11. 11. Typical Application Circuit
    12. 12. Additional Resource <ul><li>For ordering SP7656 , please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>http://www.exar.com/Common/Content/ProductDetails.aspx?ID=SP7656 </li></ul></ul><ul><li>Visit Element 14 to post your question </li></ul><ul><ul><li> www.element-14.com </li></ul></ul><ul><li>For additional inquires contact our technical service hotline or even use our “Live Technical Chat” online facility </li></ul>

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