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1
Introduction
The LM25085AEVAL evaluation board provides the design engineer with a fully functional buck regulator,
employing the LM25085A PFET switching controller which uses the constant on-time (COT) operating
principle. This evaluation board provides a 1V output over an input range of 4.5V to 24V. The circuit
delivers load currents to 5A, with current limit set at ≊8.2A. The board is populated with all components
except C5 and C7.
The board's specification are:
•
Input Voltage: 4.5V to 24V
•
Output Voltage: 1V
•
Maximum load current: 5A
•
Minimum load current: 0A
•
Current Limit Threshold: ≊8.2A
•
Measured Efficiency: 77.5% (V
output)
•
Nominal Switching Frequency: 200 kHz
•
Size: 3.1 in. x 1.5 in.
All trademarks are the property of their respective owners.
SNVA384B – February 2009 – Revised April 2013
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AN-1933 LM25085A Evaluation Board
= 4.5V, I
= 1Amp, typical efficiency for converter providing a 1V
IN
OUT
Figure 1. Evaluation Board - Top Side
Copyright © 2009–2013, Texas Instruments Incorporated
SNVA384B – February 2009 – Revised April 2013
AN-1933 LM25085A Evaluation Board
User's Guide
1
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Related Manuals for Texas Instruments LM25085A
Summary of Contents for Texas Instruments LM25085A
- Page 1 The LM25085AEVAL evaluation board provides the design engineer with a fully functional buck regulator, employing the LM25085A PFET switching controller which uses the constant on-time (COT) operating principle. This evaluation board provides a 1V output over an input range of 4.5V to 24V. The circuit delivers load currents to 5A, with current limit set at ≊8.2A.
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Page 2: Theory Of Operation
A current sink at the ADJ pin sets a constant voltage across R3. When the voltage across R5 exceeds the voltage across R3 the current limit comparator switches to shut off Q1, and the LM25085A forces a longer-than-normal off-time. The long off-time is a function of the input voltage (V... -
Page 3: Current Limit
Current Limit The LM25085A peak current limit detection operates by sensing the voltage across either the R DS(ON) Q1, or a sense resistor (R5), during the on-time and comparing it to the voltage across R3 at the ADJ pin. - Page 4 Output Ripple Control The LM25085A requires a minimum of 25 mVp-p ripple at the FB pin, in phase with the switching waveform at the SW node, for proper operation. On this evaluation board, the required ripple is generated by R7, C9, and C10, allowing the ripple at V to be kept to a minimum, as described in option A below.
- Page 5 LM25085A PGATE Pads for wire loop 6.8 PH 0.043: 3900 pF 1.1k 68 PF Figure 4. Reduced Ripple Configuration SNVA384B – February 2009 – Revised April 2013 AN-1933 LM25085A Evaluation Board Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated...
- Page 6 L1 6.8 PH wire loop 1.1k 3300 pF 48.7k 0.01 PF 68 PF Figure 6. Complete Evaluation Board Schematic AN-1933 LM25085A Evaluation Board SNVA384B – February 2009 – Revised April 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated...
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Page 7: Bill Of Materials
2010 0.01 ohm, WSL2010R0100F Resistor Vishay 0805 0 ohms CRCW08050000Z Resistor Vishay 0805 48.7k CRCW08054872F Switching Regulator LM25085 VSSOP8-EP SNVA384B – February 2009 – Revised April 2013 AN-1933 LM25085A Evaluation Board Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated... - Page 8 Figure 7. Efficiency vs Load Current Figure 8. Efficiency vs Input Voltage Figure 9. Switching Frequency vs. Input Voltage AN-1933 LM25085A Evaluation Board SNVA384B – February 2009 – Revised April 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated...
- Page 9 Circuit Performance www.ti.com Figure 10. Output Voltage Ripple Figure 11. Line Regulation Figure 12. Load Regulation SNVA384B – February 2009 – Revised April 2013 AN-1933 LM25085A Evaluation Board Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated...
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Page 10: Typical Waveforms
Trace 3 = V Trace 1 = SW Node = 12V, I Figure 15. Discontinuous Conduction Mode (Expanded Scale) AN-1933 LM25085A Evaluation Board SNVA384B – February 2009 – Revised April 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated... -
Page 11: Pc Board Layout
PC Board Layout Figure 16. Board Silkscreen Figure 17. Board Top Layer Figure 18. Board Bottom Layer (Viewed from Top) SNVA384B – February 2009 – Revised April 2013 AN-1933 LM25085A Evaluation Board Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated... -
Page 12: Important Notice
IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue.
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