EPC600 datasheet(28/30 Pages) EPC

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3.3.6. Cycle times & response time

For a common understanding, we distinguish between the cycle and the response times.

The following examples use:

■ 10MHz modulation frequency at the LED pin.

■ An integration time of 103μs.

■ A 2-wire serial clock SCLK of 1MHz.

Integration time

The integration time tINT is the timeframe in which the light is sampled by the sensor (refer to chapter 3.2.1.: Command: Commands & Inte-

gration times). It is equal the exposure time (where a shutter is open for passing the light to the sensor).

Measurement time

The time the epc600 device needs to execute a measurement from the point of receiving the command until it responds.

MEAS = 4 ⋅t INT + 770 μ s

e.g. tmeas = 4⋅103μ s + 770μ s = 1'182μ s

Communication time

It is the period from the end of the measurement until the next start in a continuous mode manner (refer to Figure 12). It is the real commu-

nication time used by the 2-wire interface and all the additional time the microprocessor needs to send the next command to the chip.

Example:

Command write:

1 check bit + 1 start bit + 8 command bits

Read response:

1 check bit + 1 start bit + 16 data bits

2-wire serial clock SCKL:

1MHz

Communication time tCOM

e.g. tcom = 10⋅1 μ s + 18⋅1 μ s = 28μ s

Data processing time

It is the period tPROCESS needed by the microprocessor for the final result: “calculation distance & quality” (refer to Figure 12)

Measurement cycle time

The measurement cycle time tCYCLE includes the duration to execute a complete measurement cycle until the next cycle propagation is pos-

sible (refer to Figure 12).

CYCLE = tMEAS + t COM + t PROCESS

e.g. tCYCLE = 1'182 μ s + 28 μ s + 100μ s = 1'310μ s

Response time

The response time denotes the necessary time interval to change the distance output DIST of the microprocessor from one state to the

other (refer to Figure 11). The maximum response time tRESPONSE of the range-finder system is given by

RESPONSE = 2 ⋅ tCYCLE

e.g. tRESPONSE = 2⋅1'310 μ s = 2'620μ s

LED on-time and LED duty cycle

For the power dissipation estimation of the emitter LED (at pin LED), the LED on-time and the duty cycle are of importance. The following

time periods have to be taken into consideration:

■ tINT

: during the integration period, the LED outputs are active for 50% of the time.

■ tMEAS

: there are 4 integration periods t INT per measurement cycle tMEAS.

■ tCOM

: during the communication time the LED outputs are not active.

The formula for the LED on-time is:

LED

−ON = 4 ⋅

INT

+ 15 μ s

e.g.

LED

−ON = 4 ⋅

103

μs

+ 15μ s = 221μ s

The LED duty cycle DCLED-ON for LED on-time versus the cycle time is

LED

−ON =

LED

−ON

CYCLE

e.g.

LED

−ON =

221

μ s

1'310

μ s

= 17%

Characteristics subject to change without notice

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Datasheet epc600 - V1.3

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