LM3905 Datasheet | National Semiconductor

Description The LM122 series are precision timers that offer great versatility with high accuracy They operate with unregulated supplies from 4 5V to 40V while maintaining constant timing periods from microseconds to hours Internal logic and regulator circuits plement the basic timing function enabling the LM122 series to operate in many different applications with a minimum of external ponents The output of the timer is a floating transistor with built in current limiting It can drive either ground referred or supply referred loads up to 40V and 50 m A The floating nature of this output makes it ideal for interfacing lamp or relay driving and signal conditioning where an open collector or emitter is required A ‘‘logic reverse’’ circuit can be programmed by the user to make the output transistor either ‘‘on’’ or ‘‘off’’ during the timing period The trigger input to the LM122 series has a threshold of 1 6V independent of supply voltage but it is fully protected against inputs as high as g 40V even when using a 5V supply The circuitry reacts only to the rising edge of the trigger signal and is immune to any trigger voltage during the timing periods An internal 3 15V regulator is included in the timer to reject supply voltage changes and to provide the user with a convenient reference for applications other than a basic timer External loads up to 5 m A can be driven by the regulator An internal 2V divider between the reference and ground sets the timing period to 1 RC The timing period can be voltage controlled by driving this divider with an external source through the VADJ pin Timing ratios of 50 1 can be easily achieved The parator used in the LM122 utilizes high gain PNP input transistors to achieve 300 p A typical input bias current over a mon mode range of 0V to 3V A boost terminal allows the user to increase parator operating current for timing periods less than 1 ms This lets the timer operate over a 3 ms to multi-hour timing range with excellent repeatability...