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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
1 n.c.
LVC1GX04 Y 6
Features
* * * * * * * + / - 24 mA output drive Multiple package options Wide supply voltage range 1.65 to 5.5 volts Wide operating temperature range -40 to +125C Demo board available Isolation of the Crystal from system loading Astable Multivibrator
Benefits
* * *
3 X1 Single chip Low Power Optimized design can be reused regardless of system load X2 4
Quick reference data
GND = 0 V; Tamb = 25C Symbol tPHL/tPLH Parameter propagation delay input X1 to output X2 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 k CL = 30 pF; RL = 500 CL = 50 pF; RL = 500 CL = 50 pF; RL = 500 CL = 50 pF; RL = 500 CL = 30 pF; RL = 1 k CL = 30 pF; RL = 500 CL = 50 pF; RL = 500 CL = 50 pF; RL = 500 CL = 50 pF; RL = 500 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
tPHL/tPLH
propagation delay input X1 to output Y
CI CPD
input capacitance power dissipation capacitance per buffer
output enabled
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 -40 to +125 C 6 SC-88 plastic SOT363 VX 74LVC1GX04GV -40 to +125 C 6 SC-74 plastic SOT457 VX4
Evaluation Board reference design schematic
VCC TP1 Test Point A U1A 3 4 1 TP2 Test Point B U1B Rf 1M R1 330 6 1 74LVC1G04GW CL 50P RL 500
C3 0.1F
74LVC1G04GW
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 sales.addresses@www.semiconductors.philips.com. A complete list will be sent to you automatically. You can also visit our website http://www.semiconductors.philips.com/sales
(c) 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
X1
CL 22P
Citizen HCM49
C2 22P
TP3 Test Point C
www.semiconductors.philips.com/logic
Published in U.S.A.

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