Section 20. Comparator Voltage Reference HIGHLIGHTS This section of the manual contains the following major topics: 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 Introduction .................................................................................................................. 20-2 Comparator Voltage Reference Control Register......................................................... 20-3 Operation ..................................................................................................................... 20-4 Interrupts...................................................................................................................... 20-6 I/O Pin Control ............................................................................................................. 20-6 Operation in Power-Saving and Debug Modes............................................................ 20-7 Effects of Resets ..........................................................................................................20-7 Related Application Notes............................................................................................ 20-8 Revision History ........................................................................................................... 20-9 20 Comparator Voltage Reference © 2007-2012 Microchip Technology Inc. DS61109G-page 20-1 PIC32 Family Reference Manual Note: This family reference manual section is meant to serve as a complement to device data sheets. Depending on the device variant, this manual section may not apply to all PIC32 devices. Please consult the note at the beginning of the “Comparator Voltage Reference” chapter in the current device data sheet to check whether this document supports the device you are using. Device data sheets and family reference manual sections are available for download from the Microchip Worldwide Web site at: http://www.microchip.com 20.1 INTRODUCTION The Comparator Voltage Reference module is a 16-tap, resistor ladder network that provides a selectable reference voltage. Although its primary purpose is to provide a reference for the analog comparators, it also may be used independently of them. A block diagram of the module is illustrated in Figure 20-1. The resistor ladder is segmented to provide two ranges of voltage reference values and has a power-down function to conserve power when the reference is not used. The module’s supply reference can be provided from either device AVDD/AVSS or an external voltage reference. The module output is available for the comparators and typically available for pin output. For more information, refer to the “Comparator Voltage Reference” chapter in the specific device data sheet. The Comparator Voltage Reference module has the following features: • • • • Figure 20-1: High-range and low-range selection Sixteen output levels available for each range Internally connected to comparators to conserve device pins Output can be connected to a pin Comparator Voltage Reference Block Diagram BGSEL<1:0>(1) 1.2V VREF+ AVDD CVRSS = 1 0.6V IVREF CVRSRC 8R CVRSS = 0 CVR<3:0> VREFSEL(1) R CVREN CVREFOUT R R 16-to-1 MUX R 16 Steps R CVREFOUT CVRCON<CVROE> R R CVRR VREFAVSS Note 1: 8R CVRSS = 1 CVRSS = 0 These bits are not available on all devices. On such devices, CVREF is generated by the resistor network and IVREF is connected to 1.2V. Refer to the “Comparator Voltage Reference” chapter in the specific device data sheet for availability. DS61109G-page 20-2 © 2007-2012 Microchip Technology Inc. Section 20. Comparator Voltage Reference 20.2 COMPARATOR VOLTAGE REFERENCE CONTROL REGISTER Register 20-1: Bit Range 31:24 23:16 15:8 7:0 CVRCON: Comparator Voltage Reference Control Register Bit 31/23/15/7 Bit 30/22/14/6 Bit 29/21/13/5 Bit 28/20/12/4 Bit 27/19/11/3 Bit 26/18/10/2 Bit 25/17/9/1 Bit 24/16/8/0 U-0 U-0 U-0 U-0 U-0 U-0 U-0 U-0 — — — — — — — — U-0 U-0 U-0 U-0 U-0 U-0 U-0 U-0 — — — — — — — — R/W-0 (1) U-0 U-0 U-0 U-0 R/W-0 R/W-0 — — — — VREFSEL(2) R/W-1 (2) U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 — CVROE CVRR CVRSS ON BGSEL<1:0> R/W-0 R/W-0 CVR<3:0> Legend: R = Readable bit -n = Value at POR W = Writable bit ‘1’ = Bit is set U = Unimplemented bit, read as ‘0’ ‘0’ = Bit is cleared x = Bit is unknown bit 31-16 Unimplemented: Read as ‘0’ ON: Comparator Voltage Reference On bit(1) 1 = Module is enabled, setting this bit does not affect other bits in the register. 0 = Module is disabled and does not consume current. Clearing this bit does not affect the other bits in the register bit 14-11 Un imp le mn ted: Read as ‘0’ bit 10 VREFSEL: Voltage Reference Select bit(2) 1 = CVREF = VREF+ 0 = CVREF is generated by the resistor network bit 9-8 BGSEL<1:0>: Band Gap Reference Source bits(2) 11 = IVREF = VREF+ 10 = Reserved 01 = IVREF = 0.6V (nominal, default) 00 = IVREF = 1.2V (nominal) bit 7 Unimplemented: Read as ‘0’ bit 6 CVROE: CVREFOUT Enable bit 1 = Voltage level is output on CVREFOUT pin 0 = Voltage level is disconnected from CVREFOUT pin bit 5 CVRR: CVREF Range Selection bit 1 = 0 to 0.67 CVRSRC, with CVRSRC/24 step size 0 = 0.25 CVRSRC to 0.75 CVRSRC, with CVRSRC/32 step size bit 4 CVRSS: CVREF Source Selection bit 1 = Comparator voltage reference source, CVRSRC = (VREF+) – (VREF-) 0 = Comparator voltage reference source, CVRSRC = AVDD – AVSS bit 3-0 CVR<3:0>: CVREF Value Selection 0 ≤ CVR<3:0> ≤ 15 bits When CVRR = 1: CVREF = (CVR<3:0>/24) • (CVRSRC) When CVRR = 0: CVREF = 1/4 • (CVRSRC) + (CVR<3:0>/32) • (CVRSRC) bit 15 2: When using 1:1 PBCLK divisor, the user software should not read or write the peripheral’s SFRs in the SYSCLK cycle immediately following the instruction that clears the module’s ON bit. These bits are not available on all devices and the reset value is ‘0’ for devices without these bits. Refer to the “Comparator Voltage Reference” chapter in the specific device data sheet for availability. © 2007-2012 Microchip Technology Inc. DS61109G-page 20-3 Comparator Voltage Reference Note 1: 20 PIC32 Family Reference Manual 20.3 OPERATION 20.3.1 CVREF Output The Comparator Voltage Reference module is controlled through the CVRCON register (Register 20-1). This module provides two ranges of output voltage, each with 16 distinct levels. The range to be used is selected by the CVRR bit (CVRCON<5>). The primary difference between the ranges is the size of the steps selected by the CVREF value selection bits, CVR<3:0>, with one range offering finer resolution and the other offering a wider range of output voltage. The typical output voltages are listed in Table 20-1. The equations used to calculate the CVREF output are as follows: If CVRR = 1: Voltage Reference = ((CVR<3:0>)/24) x (CVRSRC) If CVRR = 0: Voltage Reference = (CVRSRC/4) + ((CVR<3:0>)/32) x (CVRSRC) The CVREF Source Voltage (CVRSRC) can come from either AVDD and AVSS, or the external VREF+ and VREF- pins that are multiplexed with I/O pins. The voltage source is selected by the CVRSS bit (CVRCON<4>). The voltage reference is output to the CVREFOUT pin by setting the CVROE bit (CVRCON<6>), which overrides the corresponding TRIS bit setting. The settling time of the Comparator Voltage Reference module must be considered when changing the CVREF output. For more information, refer to the “Comparator Voltage Reference” chapter in the specific device data sheet. Table 20-1: CVR<3:0> DS61109G-page 20-4 Typical Voltage Reference in Volts (CVRSRC = 3.3) Voltage Reference CVRR = 0 (CVRCON<5>) CVRR = 1 (CVRCON<5>) 0 0.83V 0.00V 1 0.93V 0.14V 2 1.03V 0.28V 3 1.13V 0.41V 4 1.24V 0.55V 5 1.34V 0.69V 6 1.44V 0.83V 7 1.55V 0.96V 8 1.65V 1.10V 9 1.75V 1.24V 10 1.86V 1.38V 11 1.96V 1.51V 12 2.06V 1.65V 13 2.17V 1.79V 14 2.27V 1.93V 15 2.37V 2.06V © 2007-2012 Microchip Technology Inc. Section 20. Comparator Voltage Reference 20.3.2 CVREF Output Considerations The full range of voltage reference cannot be realized due to the construction of the module. The transistors on the top and bottom of the resistor ladder network (see Figure 20-1) keep the voltage reference from approaching the reference source rails. The voltage reference is derived from the reference source. Therefore, the voltage reference output changes with fluctuations in that source. Refer to the “Electrical Characteristics” chapter in the specific device data sheet for the electrical specifications. Table 20-2 lists the typical output impedances for the Comparator Voltage Reference module. Table 20-2: Typical CVREF Output Impedance in kilohms CVR<3:0> Voltage Reference CVRR = 0 (CVRCON<5>) CVRR = 1 (CVRCON<5>) 12k 0.5k 1 13k 1.9k 2 13.8k 3.7k 3 14.4k 5.3k 4 15k 6.7k 5 15.4k 7.9k 6 15.8k 9k 7 15.9k 9.9k 8 16k 10.7k 0 9 15.9k 11.3k 10 15.8k 11.7k 11 15.4k 11.9k 12 15k 12k 13 14.4k 11.9k 14 13.8k 11.7k 15 12.9k 11.3k 20.3.3 IVREF Output The Comparator Voltage Reference module provides selection for the internal voltage reference. The Band Gap Reference Source Select bits (BGSEL<1:0>) allow voltage selection of 1.2V or 0.6V, which is generated internally. Refer to the “Electrical Characteristics” chapter in the specific device data sheet for the IVREF specifications. 20 Comparator Voltage Reference © 2007-2012 Microchip Technology Inc. DS61109G-page 20-5 PIC32 Family Reference Manual 20.4 INTERRUPTS There are no Interrupt Configuration registers or bits for the Comparator Voltage Reference module. The Comparator Voltage Reference module does not generate interrupts. 20.5 I/O PIN CONTROL The Comparator Voltage Reference module can output to a pin. When the module is enabled and the CVROE bit (CVRCON<6>) is ‘1’, the output driver for the CVREFOUT pin is disabled and the CVREF voltage is available at the pin. For operation, the TRISx bit corresponding to the CVREFOUT pin must be a ‘1’. This disables the digital input mode for the pin and prevents undesired current draw resulting from applying an analog voltage to a digital input pin. The output buffer has very limited drive capability. An external buffer amplifier is recommended for any application that uses the CVREF voltage externally. An output capacitor may be used to reduce output noise. Use of an output capacitor will increase settling time (see Figure 20-2). Figure 20-2: Comparator Voltage Reference Output Buffer Example Comparator Voltage Reference Module DS61109G-page 20-6 R(1) Voltage Reference Output Impedance CVREF C(2) + – Buffered Voltage Reference Output Note 1: R is dependent on the Comparator Voltage Reference Control bits CVRR (CVRCON<5>) and CVR<3:0> (CVRCON<3:0>). For more information, see Table 20-2. 2: Use of an output capacitor will increase settling time. Capacitor value selection is dependent on the CVR<3:0> and CVRR settings, and the frequency to be attenuated. © 2007-2012 Microchip Technology Inc. Section 20. Comparator Voltage Reference 20.6 OPERATION IN POWER-SAVING AND DEBUG MODES 20.6.1 Operation in Sleep Mode The Comparator Voltage Reference module continues to operate in Sleep mode. The CVRCON register is not affected when the device enters or wakes from Sleep mode. If the CVREF voltage is not used in Sleep mode, the module can be disabled by clearing the ON bit (CVRCON<15>) prior to entering Sleep mode to conserve power. 20.6.2 Operation in Idle Mode The Comparator Voltage Reference module continues to operate in Idle mode. The CVRCON register is not affected when the device enters or exits Idle mode. There is no provision to automatically disable the module in Idle mode. If the CVREF voltage is not used in Idle mode, the module can be disabled by clearing the ON bit (CVRCON<15>) prior to entering Idle mode to conserve power. 20.6.3 Operation in Debug Mode The Comparator Voltage Reference module continues to operate while the device is in Debug mode. The module does not support Freeze mode. 20.7 EFFECTS OF RESETS All resets disable the voltage reference by forcing all bits in the CVRCON register to ‘0’. 20 Comparator Voltage Reference © 2007-2012 Microchip Technology Inc. DS61109G-page 20-7 PIC32 Family Reference Manual 20.8 RELATED APPLICATION NOTES This section lists application notes that are related to this section of the manual. These application notes may not be written specifically for the PIC32 family device family, but the concepts are pertinent and could be used with modification and possible limitations. The current application notes related to the Comparator Voltage Reference module are: Title Application Note # Related application notes are not available. Note: DS61109G-page 20-8 N/A Please visit the Microchip web site (www.microchip.com) for additional application notes and code examples for the PIC32 family of devices. © 2007-2012 Microchip Technology Inc. Section 20. Comparator Voltage Reference 20.9 REVISION HISTORY Revision A (October 2007) This is the initial released version of this document. Revision B (October 2007) Updated document to remove Confidential status. Revision C (April 2008) Revised status to Preliminary; Revised U-0 to r-x. Revision D (June 2008) Revised Figure 20-1; Change Reserved bits from “Maintain as” to “Write”; Added Note to ON bit (CVRCON Register). Revision E (August 2010) This revision includes the following updates: • Updated the Comparator Voltage Reference Block Diagram (see Figure 20-1) • Added notes regarding the INV, SET, and CLR registers to the Oscillators SFR Summary (see Table 20-1) • Updated the Comparator Voltage Reference Control Register (see Register 20-1) • Removed the CVRCONINV, CVRCONSET, and CVRCONCLR registers • Removed 20.3.3 “Initialization” • Added new section 20.3.3 “IVREF Output” • Removed Table 20-4: Pins Associated with a Comparator • Removed 20.8 “Design Tips” • Minor corrections to formatting and text were incorporated throughout the document Revision F (May 2011) This revision includes the following updates: • Updated the Comparator Voltage Reference Block Diagram (see Figure 20-1) • Removed the Comparator Voltage Reference SFR Summary (Table 20-1) and related text • Updated the BGSEL<1:0> bit value for ‘10’ to Reserved and modified the Notes in the CVRCON register (see Register 20-1) • Updated the allowable voltage reference selections in 20.3.3 “IVREF Output” • Minor updates to text and formatting were incorporated throughout the document Revision G (May 2012) This revision includes the following updates: • Changed references to VSS and VDD to: AVSS and AVDD, respectively, in 20.1 “Introduction” and 20.3.1 “CVREF Output” • Minor updates to text and formatting were incorporated throughout the document 20 Comparator Voltage Reference © 2007-2012 Microchip Technology Inc. DS61109G-page 20-9 PIC32 Family Reference Manual NOTES: DS61109G-page 20-10 © 2007-2012 Microchip Technology Inc. Note the following details of the code protection feature on Microchip devices: • Microchip products meet the specification contained in their particular Microchip Data Sheet. • Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the intended manner and under normal conditions. • There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data Sheets. Most likely, the person doing so is engaged in theft of intellectual property. • Microchip is willing to work with the customer who is concerned about the integrity of their code. • Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as “unbreakable.” Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act. Information contained in this publication regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer’s risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights. Trademarks The Microchip name and logo, the Microchip logo, dsPIC, KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro, PICSTART, PIC32 logo, rfPIC and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor, MXDEV, MXLAB, SEEVAL and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. Analog-for-the-Digital Age, Application Maestro, chipKIT, chipKIT logo, CodeGuard, dsPICDEM, dsPICDEM.net, dsPICworks, dsSPEAK, ECAN, ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial Programming, ICSP, Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB, MPLINK, mTouch, Omniscient Code Generation, PICC, PICC-18, PICDEM, PICDEM.net, PICkit, PICtail, REAL ICE, rfLAB, Select Mode, Total Endurance, TSHARC, UniWinDriver, WiperLock and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. SQTP is a service mark of Microchip Technology Incorporated in the U.S.A. All other trademarks mentioned herein are property of their respective companies. © 2007-2012, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. ISBN: 978-1-62076-303-2 QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV == ISO/TS 16949 == © 2007-2012 Microchip Technology Inc. Microchip received ISO/TS-16949:2009 certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona; Gresham, Oregon and design centers in California and India. The Company’s quality system processes and procedures are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and analog products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001:2000 certified. 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