OPF794 Optek, OPF794 Datasheet - Page 26

• Manufacturer Part Number: OPF794
• Description: Photodiodes Pin Photodiode
• Manufacturer: Optek

Specifications of OPF794

• Maximum Reverse Voltage: 100 V
• Maximum Rise Time: 6 ns
• Mounting Style: SMD/SMT
• Product: Photodiode
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PhotoLogic
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Page B—6
Product Definitions
OTEM
UTPUT
Historically optoelectronic components such as phototransistors have been analog output devices. The designer had to design
with an output current from the phototransistor generated by a given input bias circuit. The advent of integrated circuits and
microprocessors has required the electronics world to turn digital. Sophisticated electronics today communicate by logic levels
of 1’s or O’s. This means that the design engineer must now convert the analog light current of a phototransistor to a voltage
level in order to communicate the sensing function to downstream processing electronics. This signal processing represents
additional system cost in components and performance specification guardbanding which can be reflected in the unit pricing
of the optoelectronic component or assembly.
Photologic® discrete components utilize the best of the analog characteristics of optoelectronic components and the signal
processing capabilities of linear integrated circuits and combines the two on one chip. The stable response and speed of a
photodiode is used as an input to trigger the onboard integrated circuitry. The output of the optoelectronic component
provides the designer a logic level output, instead of an analog current. This saves the end user processing circuitry system cost
and affords performance specifications which are more easily designed and integrated into their application. In other words,
single switching to an on/off state, or dynamically switched signals, as in encoders, to multiple on/off states. The resulting
output will be a high logic level (1), low logic level (0) or corresponding pulse train corresponding to the synamic triggering. All
Photologic® devices have internal regulation.
The Photologic® family of photointegrated circuits is available with various output options. The output options for the buffer
types (high logic level with light sensed) and inverter types (low logic level with light sensed) are a totem-pole output, 10K
load resistor or open-collector output. These optional output configurations are offered to afford the design engineer the most
versatility in addressing their system applications.
A totem-pole configuration is very popular due to its inherent low output resistance for both a high and low output level. The
low level output resistance will be the resistance at the collector of a saturated output transistor, typically in the order of 10
ohms. The high level output resistance in a totem-pole output is that of an emitter follower configuration. This is typically less
than 100 ohms as compared to most collector load resistance values in the 1 kilo ohms range. The low output resistance of
the totem-pole configuration in both high and low output level allows a more rapid charge and discharge of any load
capacitance at the output. This results in comparable high to low and low to high transition times.
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Issue A.1 2005
OPTEK Technology Inc. www.optekinc.com