74LVC1GX04 One chip crystal oscillator driver Semiconductors Description The 74LVC1GX04 combines the functions of the 74LVC1GU04 and 74LVC1G04 into a single package to provide a device optimized for use in crystal oscillator applications. This integration produces the benefits of a compact footprint, lower power dissipation, and stable operation over a wide range of frequency and temperature. The device is fully specified for partial power-down applications using Ioff at output Y. This disables the output, preventing damaging backflow current when the device is powered down. Applications • • Crystal Oscillator Astable Multivibrator n.c. Y 6 3 X1 Single chip Low Power Optimized design can be reused regardless of system load X2 4 Features Benefits • • • • • • • • • • + / - 24 mA output drive Multiple package options Wide supply voltage range 1.65 to 5.5 volts Wide operating temperature range -40 to +125ºC Demo board available Isolation of the Crystal from system loading Astable Multivibrator LVC1GX04 1 Quick reference data GND = 0 V; Tamb = 25˚C Symbol tPHL/tPLH Parameter propagation delay input X1 to output X2 tPHL/tPLH propagation delay input X1 to output Y CI CPD input capacitance power dissipation capacitance per buffer VCC = 1.8 V; VCC = 2.5 V; VCC = 2.7 V; VCC = 3.3 V; VCC = 5.0 V; VCC = 1.8 V; VCC = 2.5 V; VCC = 2.7 V; VCC = 3.3 V; VCC = 5.0 V; Conditions CL = 30 pF; RL = 1 kΩ CL = 30 pF; RL = 500 Ω CL = 50 pF; RL = 500 Ω CL = 50 pF; RL = 500 Ω CL = 50 pF; RL = 500 Ω CL = 30 pF; RL = 1 kΩ CL = 30 pF; RL = 500 Ω CL = 50 pF; RL = 500 Ω CL = 50 pF; RL = 500 Ω CL = 50 pF; RL = 500 Ω output enabled Typical 2.1 1.7 2.5 2.1 1.6 4.1 2.9 3.0 2.8 2.3 5 35 Unit ns ns ns ns ns ns ns ns ns ns pF pF 74LVC1GX04 One chip crystal oscillator driver w w w. s e m i c o n d u c t o r s . p h i l i p s . c o m In designing a crystal oscillator, the values of C1 and C2 as shown in the reference design are dependent on the selected crystal. R1 is critical to the start up performance and drive level to the crystal. Because the system load is isolated by the internal buffer in the 74LVC1GX04, these calculations can be done once for many different system loads. For the reference design as shown, the crystal load capacitance (CL) should be equal to the capacitance C1 and C2 in parallel in addition to any stray capacitance (Cs) C1 and C2 should be equal and the designer can use the following formula to calculate the value: CL = (C1*C2) / (C1+C2) +Cs Where: CL is the load capacitance as specified by the crystal manufacturer, Cs is the stray capacitance of the circuit which is equal to the input capacitance of the 74LVC1GX04 of 5 pF. The feedback resistor (Rf) provides negative feedback and sets a bias point for the un-buffered inverter. This value is not critical and is typically 1 Meg. The starting value for R1 should be equal to the reactance of C2 at the crystal frequency. (R1 = XC2) This will result in an input to the crystal of 50% of the rail to rail output of X2. Usually this keeps the drive level into the crystal within the drive specifications of the crystal but the designer should verify this. Overdriving the crystal can cause damage. After the calculations are performed for a particular crystal, the oscillator circuit should be tested. The following simple checks will verify the prototype design of a crystal controlled oscillator: • Test the oscillator over worse case conditions of min-max operating voltage and temperature.You can also simulate worse case crystal variations by adding series and parallel resistors. • Insure that the circuit does not oscillate when the crystal is removed. • Check the frequency stability over a supply range slightly greater than which is likely to occur during normal operation. • Check that the start up time is within system requirements. Ordering information Packages Part Number Temp. Range Pins Package Material Code Marking 74LVC1GX04GW -40º to +125º C 6 SC-88 plastic SOT363 VX 74LVC1GX04GV -40º to +125º C 6 SC-74 plastic SOT457 VX4 Evaluation Board reference design schematic VCC TP1 Test Point A C3 0.1µF U1A 3 1 4 TP2 Test Point B 74LVC1G04GW U1B Rf 1 6 1M X1 CL 22P Citizen HCM49 74LVC1G04GW R1 330 C2 22P CL 50P TP3 Test Point C RL 500 Philips Semiconductors Philips Semiconductors is a worldwide company with over 100 sales offices in more than 50 countries. For a complete up-to-date list of our sales offices please e-mail [email protected]. A complete list will be sent to you automatically. You can also visit our website http://www.semiconductors.philips.com/sales www.semiconductors.philips.com/logic © Koninklijke Philips Electronics N.V. 2003 All rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner.The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor imply any license under patent- or other industrial or intellectual property rights. Date of release: August 2003 document order number: 9397 750 11958 Published in U.S.A.