AN2 Using the Microchip TC54 Voltage Detector INTRODUCTION OPERATION Microchip's TC54 series of voltage detectors are designed to supersede a variety of discrete comparator circuits and bipolar technology voltage detectors. The TC54 equivalent circuit is shown in Figure 1. The internal precision temperature-compensated reference and comparator circuit consistently monitor VIN for an under-voltage condition. When such a condition occurs, the output is forced to the active (LOW) state and remains there until VIN is once again within tolerance. As shown in the timing diagram of Figure 1, the output is forced active when VIN < (-VDET) (Where (-VDET) is the threshold voltage) and returns HIGH when VIN exceeds (-VDET) plus 5% hysteresis (example: if (-VDET) = 2.0V, the output will go HIGH when VIN > 2.1V). These voltage detectors are especially suited for application in battery powered systems because of their extremely low 1A operating current. Each part is laser programmed to the desired trip point voltage over the range of 1.1V to 6.0V in 100mV steps. For complete design flexibility, complementary or open-drain output versions are available. TC54 package options include surface mount SOT-23A and SOT-89 or through-hole TO-92 types. TC54VC only Input Voltage 2 Release Voltage (+VDET) Hysteresis Voltage Detect Voltage (-VDET) VIN Minimum Operating Voltage Ground Level - + VOUT 1 Output Voltage VREF VSS 3 Ground Level FIGURE 1: TC54 block diagram and timing. TC54 AS A MICROCONTROLLER RESET GENERATOR Reset generators external to the microcontroller are necessary in systems that have slowly rising power supplies. It is necessary to hold the microcontroller in its reset state until the power supply has reached a valid operating level. Commonly used simple Schmitt trigger/capacitor circuits are inadequate since they do not accurately monitor the power supply voltage tolerance. The TC54 series overcomes this problem with precise voltage detection. Figure 2 shows a reset circuit using a TC54 replacing bipolar integrated voltage detectors (see Table 1). VIN VIN TC54VC VOUT R MCLR PIC Microcontroller 100 VSS FIGURE 2: Microcontroller reset circuit using TC54. (c) 2001 Microchip Technology, Inc. DS00779A-page 1 AN2 MFGR MICROCHIP PART# MICROCHIP # DESCRIPTION ATTRIBUTE Motorola Motorola Motorola Motorola Motorola Motorola T.I. T.I. MC33064P-5 MC34064P-5 MC34164P-3 MC34164P-5 MC33164P-3 MC33164P-5 TL7757ILP TL7757CLP TC54VN4502EZB TC54VN4502EZB TC54VN2702EZB TC54VN4302EZB TC54VN2702EZB TC54VN4302EZB TC54VN4502EZB TC54VN4502EZB 4.5V trip, -40 to +85C, TO-92 4.5V trip, 0 to +70C, TO-92 2.7V trip, 0 to +70C, TO-92 4.3V trip, 0 to +70C, TO-92 2.7V trip, -40 to +85C, TO-92 4.3V trip, -40 to +85C, TO-92 4.5V trip, -40 to +85C, TO-92 4.5V trip, 0 to +70C, TO-92 500 times less power 500 times less power 10 times less power 10 times less power 10 times less power 10 times less power 2000 times less power 2000 times less power Table 1: TC54 cross reference listing. MODIFYING THE TRIP POINT, -VDET Although the TC54 has a pre-programmed -VDET, it is sometimes necessary to make adjustments during prototyping. This can be accomplished by connecting an external resistor divider to a TC54 which has a -VDET lower than that of VSOURCE (Figure 3). To maintain detector accuracy, the bleeder current through the divider should be significantly higher than the 1A operating current required by the TC54. A reasonable value for this bleeder current is 100A (100 times the 1A required by the TC54). For example, if -VDET = 2V and the desired trip point is 2.5V, the value of R1 + R2 is 25k (2.5V/100A). The value of R1 + R2 can be rounded to the nearest standard value and plugged into the equation of Figure 3 to calculate values for R1 and R2. 1% tolerance resistors are recommended. VSOURCE VSOURCE R2 R1 R1 + R2 ) = (-V DET ) Where: VIN R1 ( TC54 VOUT VSS VSOURCE = Voltage to be monitored (-VDET) = Threshold Voltage Setting of TC54 Note:In this example, VSOURCE must be greater than (-VDET) Figure 3: Modify trip point of TC54 using external resistor divider. DS00779A-page 2 (c) 2001 Microchip Technology, Inc. AN2 4.3V VCC 270 VIN VIN TC54VN RL Pwr Sply VOUT TC54Vx VOUT Power Good MTP3055EL VSS VSS Figure 4: MOSFET low drive protection. Figure 6: Power good monitor. OTHER APPLICATIONS VIN TC54Vx VOUT VSS BATLOW Low operating power and small physical size make the TC54 series ideal for many voltage detector applications, such as those shown in Figures 4, 5 and 6. Figure 4 shows a low-voltage gate drive protection circuit, which prevents overheating of the logic-level MOSFET due to insufficient gate voltage. When the input signal is below the threshold of the TC54VN, its output grounds the gate of the MOSFET. Figures 5 and 6 show the TC54 in conventional voltage monitoring applications. Figure 5: Battery voltage monitor. (c) 2001 Microchip Technology, Inc. DS00779A-page 3 AN2 Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. No representation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip's products as critical components in life support systems is not authorized except with express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property rights. Trademarks The Microchip name and logo, the Microchip logo, PIC, PICmicro, PICMASTER, PICSTART, PRO MATE, KEELOQ, SEEVAL, MPLAB and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. Total Endurance, ICSP, In-Circuit Serial Programming, FilterLab, MXDEV, microID, FlexROM, fuzzyLAB, MPASM, MPLINK, MPLIB, PICC, PICDEM, PICDEM.net, ICEPIC, Migratable Memory, FanSense, ECONOMONITOR, Select Mode and microPort are trademarks of Microchip Technology Incorporated in the U.S.A. Serialized Quick Term Programming (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. (c) 2001, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. Microchip received QS-9000 quality system certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona in July 1999. The Company's quality system processes and procedures are QS-9000 compliant for its PICmicro(R) 8-bit MCUs, KEELOQ(R) code hopping devices, Serial EEPROMs and microperipheral products. In addition, Microchip's quality system for the design and manufacture of development systems is ISO 9001 certified. DS00779A-Page 4 2001 Microchip Technology Inc AN2 WORLDWIDE SALES AND SERVICE AMERICAS ASIA/PACIFIC Japan Corporate Office Australia 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7200 Fax: 480-792-7277 Technical Support: 480-792-7627 Web Address: http://www.microchip.com Microchip Technology Australia Pty Ltd Suite 22, 41 Rawson Street Epping 2121, NSW Australia Tel: 61-2-9868-6733 Fax: 61-2-9868-6755 Microchip Technology Japan K.K. Benex S-1 6F 3-18-20, Shinyokohama Kohoku-Ku, Yokohama-shi Kanagawa, 222-0033, Japan Tel: 81-45-471- 6166 Fax: 81-45-471-6122 Rocky Mountain China - Beijing 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7966 Fax: 480-792-7456 500 Sugar Mill Road, Suite 200B Atlanta, GA 30350 Tel: 770-640-0034 Fax: 770-640-0307 Microchip Technology Consulting (Shanghai) Co., Ltd., Beijing Liaison Office Unit 915 New China Hong Kong Manhattan Bldg. No. 6 Chaoyangmen Beidajie Beijing, 100027, No. China Tel: 86-10-85282100 Fax: 86-10-85282104 Austin - Analog China - Chengdu 8303 MoPac Expressway North Suite A-201 Austin, TX 78759 Tel: 512-345-2030 Fax: 512-345-6085 Microchip Technology Consulting (Shanghai) Co., Ltd., Chengdu Liaison Office Rm. 2401, Ming Xing Financial Tower No. 88 TIDU Street Chengdu 610016, China Tel: 86-28-6766200 Fax: 86-28-6766599 Atlanta Boston 2 Lan Drive, Suite 120 Westford, MA 01886 Tel: 978-692-3848 Fax: 978-692-3821 Boston - Analog Unit A-8-1 Millbrook Tarry Condominium 97 Lowell Road Concord, MA 01742 Tel: 978-371-6400 Fax: 978-371-0050 Chicago 333 Pierce Road, Suite 180 Itasca, IL 60143 Tel: 630-285-0071 Fax: 630-285-0075 Dallas 4570 Westgrove Drive, Suite 160 Addison, TX 75001 Tel: 972-818-7423 Fax: 972-818-2924 Dayton Two Prestige Place, Suite 130 Miamisburg, OH 45342 Tel: 937-291-1654 Fax: 937-291-9175 Detroit Tri-Atria Office Building 32255 Northwestern Highway, Suite 190 Farmington Hills, MI 48334 Tel: 248-538-2250 Fax: 248-538-2260 Los Angeles 18201 Von Karman, Suite 1090 Irvine, CA 92612 Tel: 949-263-1888 Fax: 949-263-1338 New York 150 Motor Parkway, Suite 202 Hauppauge, NY 11788 Tel: 631-273-5305 Fax: 631-273-5335 San Jose Microchip Technology Inc. 2107 North First Street, Suite 590 San Jose, CA 95131 Tel: 408-436-7950 Fax: 408-436-7955 Toronto 6285 Northam Drive, Suite 108 Mississauga, Ontario L4V 1X5, Canada Tel: 905-673-0699 Fax: 905-673-6509 China - Fuzhou Microchip Technology Consulting (Shanghai) Co., Ltd., Fuzhou Liaison Office Rm. 531, North Building Fujian Foreign Trade Center Hotel 73 Wusi Road Fuzhou 350001, China Tel: 86-591-7557563 Fax: 86-591-7557572 China - Shanghai Microchip Technology Consulting (Shanghai) Co., Ltd. Room 701, Bldg. B Far East International Plaza No. 317 Xian Xia Road Shanghai, 200051 Tel: 86-21-6275-5700 Fax: 86-21-6275-5060 China - Shenzhen Microchip Technology Consulting (Shanghai) Co., Ltd., Shenzhen Liaison Office Rm. 1315, 13/F, Shenzhen Kerry Centre, Renminnan Lu Shenzhen 518001, China Tel: 86-755-2350361 Fax: 86-755-2366086 Hong Kong Korea Microchip Technology Korea 168-1, Youngbo Bldg. 3 Floor Samsung-Dong, Kangnam-Ku Seoul, Korea 135-882 Tel: 82-2-554-7200 Fax: 82-2-558-5934 Singapore Microchip Technology Singapore Pte Ltd. 200 Middle Road #07-02 Prime Centre Singapore, 188980 Tel: 65-334-8870 Fax: 65-334-8850 Taiwan Microchip Technology Taiwan 11F- 3, No. 207 Tung Hua North Road Taipei, 105, Taiwan Tel: 886-2-2717-7175 Fax: 886-2-2545-0139 EUROPE Denmark Microchip Technology Denmark ApS Regus Business Centre Lautrup hoj 1-3 Ballerup DK-2750 Denmark Tel: 45 4420 9895 Fax: 45 4420 9910 France Arizona Microchip Technology SARL Parc d'Activite du Moulin de Massy 43 Rue du Saule Trapu Batiment A - ler Etage 91300 Massy, France Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79 Germany Arizona Microchip Technology GmbH Gustav-Heinemann Ring 125 D-81739 Munich, Germany Tel: 49-89-627-144 0 Fax: 49-89-627-144-44 Microchip Technology Hongkong Ltd. Unit 901, Tower 2, Metroplaza 223 Hing Fong Road Kwai Fong, N.T., Hong Kong Tel: 852-2401-1200 Fax: 852-2401-3431 Germany - Analog India Arizona Microchip Technology SRL Centro Direzionale Colleoni Palazzo Taurus 1 V. Le Colleoni 1 20041 Agrate Brianza Milan, Italy Tel: 39-039-65791-1 Fax: 39-039-6899883 Microchip Technology Inc. India Liaison Office Divyasree Chambers 1 Floor, Wing A (A3/A4) No. 11, O'Shaugnessey Road Bangalore, 560 025, India Tel: 91-80-2290061 Fax: 91-80-2290062 Lochhamer Strasse 13 D-82152 Martinsried, Germany Tel: 49-89-895650-0 Fax: 49-89-895650-22 Italy United Kingdom Arizona Microchip Technology Ltd. 505 Eskdale Road Winnersh Triangle Wokingham Berkshire, England RG41 5TU Tel: 44 118 921 5869 Fax: 44-118 921-5820 06/01/01 (c) 2001 Microchip Technology, Inc. DS00779A-page 5