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Dt Sheet. The ICL requires a voltage in excess of 1. All Rights Reserved FN This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. The maximum output current of the ICL is limited by design to 15mA under any operating conditions. The maximum output current of the ICL is not defined. And systems using the ICL must therefore ensure that the output current does not exceed 30mA and that the maximum power dissipation of the device is not exceeded.
Threshold Trip Voltage is 0. This reference voltage is close to the value of the bandgap voltage for silicon and is highly stable with respect to both temperature and supply voltage. The deviation from the bandgap voltage is necessary due to the negative temperature coefficient of the thin film resistors ppm per oC. This ensures a constant current supply free from variations. Leakage current in the transistors is not sufficient in itself to guarantee reliable startup. To generate the bandgap voltage, it is necessary to sum a voltage equal to the base emitter voltage of Q9 to a voltage proportional to the difference of the base emitter voltages of two transistors Q8 and Q9 operating at two current densities.
It is advisable to externally limit this current to 25mA or less. Applications The ICL and ICL are similar in many respects, especially with regard to the setup of the input trip conditions and hysteresis circuitry.
The following discussion describes both devices, and where differences occur they are clearly noted.
Also, prolonged operation above this voltage will lead to degradation of device characteristics. Input and output waveforms are shown in Figure 21 for a simple 1. A principal application of the ICL is voltage level detection, and for that reason the OUTPUT current has been limited to typically 7mA to permit direct drive of an LED connected to the positive supply without a series current limiting resistor.
On the other hand the ICL is intended for applications such as programmable zener references, and voltage regulators where output currents well in excess of 7mA are desirable. Therefore, the output of the ICL is not current limited, and if the output is used to drive an LED, a series current limiting resistor must be used.
In most applications an input resistor divider network may be used to generate the 1. Case 1. The principle behind hysteresis is to provide positive feedback to the input trip point such that there is a voltage difference between the input voltage necessary to turn the outputs ON and OFF. The advantage of hysteresis is especially apparent in electrically noisy environments where simple but positive voltage detection is required.
Hysteresis circuitry, however, is not limited to applications requiring better noise performance but may be expanded into highly complex systems with multiple voltage level detection and memory applications-refer to specific applications section. These are shown in Figure Simple voltage detection no hysteresis Unless an input voltage of approximately 1.
R3 will provide hysteresis if required. For low values of hysteresis, circuit Figure 27B is to be preferred due to the offset voltage of the hysteresis output transistor. On power up the initial condition is A. On momentarily closing switch S1 the operating point changes to B and will remain at B until the supply voltage drops below VTR1, at which time the output will revert to condition A. Nonvolatile Power Supply Malfunction Recorde Figure 30 and Figure 31 In many systems a transient or an extended abnormal or absence of a supply voltage will cause a system failure.
This failure may take the form of information lost in a volatile semiconductor memory stack, a loss of time in a timer or even possible irreversible damage to components if a supply voltage exceeds a certain value.
Upon power up to the normal operating voltage this record must have been retained and easily interrogated. This could be important in the case of a transient power failure due to a faulty component or intermittent power supply, open circuit, etc.
A simple circuit to record an out of range voltage excursion may be constructed using an ICL, an ICL plus a few resistors. This circuit will operate to 30V without exceeding the maximum ratings of the ICs. The two voltage limits defining the in range supply voltage may be set to any value between 2. The ICL is used to detect a voltage, V 2, which is the upper voltage limit to the operating voltage range.
The ICL detects the lower voltage limit of the operating voltage range, V1. Hysteresis is used with the ICL so that the output can be stable in either state over the operating voltage range V1 to V 2 by making V3 - the upper trip point of the ICL much higher in voltage than V2.
This may be achieved only by shorting out R3 for values of supply voltage between V 1 and V2. The equivalent parallel resistance is in the tens of megohms over the supply voltage range of 2V to 30V.
These constant current sources may be used to provide basing for various circuitry including differential amplifiers and comparators. See Typical Operating Characteristics for complete information.
The knee is sharper and occurs at a significantly lower current than other similar devices available. Applications would therefore include battery operated equipment especially those operating at low voltages.
For circuits consuming less than 5mA this may be achieved using an ICL driving the load directly. For higher load currents it is necessary to use an external pnp transistor or darlington pair driven by the output of the ICL Resistors R1 and R2 set up the disconnect voltage and R3 provides optional voltage hysteresis if so desired. The output voltage is simply programmed, using a resistor divider network R1 and R2. The output circuit consisting of R 3, R 4 and C2 results in a slow output positive ramp.
The negative range is much faster than the positive range. R5 and R6 provide hysteresis so that under all circumstances the second ICL is turned on for sufficient time to discharge C3. Depending upon the desired output polarities for low and high input frequencies, either an ICL or an ICL may be used as the output driver. SPST switches range from push button and slide types to calculator keyboards.
A major problem with the use of switches is the mechanical bounce of the electrical contacts on closure. Contact bounce times can range from a fraction of a millisecond to several tens of milliseconds depending upon the switch type.
During this contact bounce time the switch may make and break contact several times. The circuit shown in Figure 37 provides a rapid charge up of C1 to close to the positive supply This circuit is sensitive to supply voltage variations and should be used with a stabilized power supply.
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