RE46C190 datasheet(22/42 Pages) MICROCHIP

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RE46C190

DS22271A-page 22

 2010 Microchip Technology Inc.

4.3

Smoke Calibration

A separate calibration mode is entered for each

measurement mode (Normal, Hysteresis, Hush and

Chamber Test) so that independent limits can be set for

each. In all calibration modes, the integrator output can

be accessed at the GLED output.

The Gamp output voltage, which represents the smoke

detection level, can be accessed at the RLED output.

The SmkComp output voltage is the result of the

comparison of Gamp with the integrator output, and

can be accessed at HB. The FEED input can be

clocked to step up the smoke detection level at RLED.

Once the desired smoke threshold is reached, the

TEST input is pulsed low to high to store the result.

The procedure is described in the following steps:

Power up with the bias conditions shown in

Figure 4-1.

Drive TEST2 input from VSS to VDD to enter the

Programming mode. TEST2 should remain at

VDD through Step 8 described below.

Apply a clock pulse to the TEST input to enter in

T1 mode. This initiates the calibration mode for

Normal Limits setting. The Integrator output saw

tooth should appear at GLED and the smoke

detection level at RLED. Clock FEED to

increase the smoke detection level as needed.

Once the desired smoke threshold is reached,

the IO input is pulsed low to high to enter the

result. See typical waveforms in Figure 4-4.

Operating the circuit in this manner, with nearly

continuous IRED current for an extended period

of time, may result in undesired or excessive

heating of the part. The duration of this step

should be minimized.

Apply a second clock pulse to the TEST input to

enter in T2 mode. This initiates the calibration

mode for Hysteresis Limits. Clock FEED as in

Step 3 and apply pulse to IO, once desired level

is reached.Operating the circuit in this manner,

with nearly continuous IRED current for an

extended period of time, may result in undesired

or excessive heating of the part. The duration of

this step should be minimized.

Apply a clock pulse to the TEST input again to

enter in T3 mode and initiate calibration for Hush

Limits. Clock FEED as in the steps above and

apply a pulse to IO, once the desired level is

reached. Operating the circuit in this manner,

with nearly continuous IRED current for an

extended period of time, may result in undesired

or excessive heating of the part. The duration of

this step should be minimized.

Apply a clock pulse to the TEST input a fourth

time to enter in T4 mode, and initiate the

calibration for Chamber Test Limits. Clock FEED

and apply pulse to IO, once desired level is

reached. Operating the circuit in this manner,

with nearly continuous IRED current for an

extended period of time, may result in undesired

or excessive heating of the part. The duration of

this step should be minimized.

If the Long Term Drift Adjustment is enabled,

after all limits have been set, the long term drift

(LTD) baseline measurement must be made. To

do this, a measurement must be made under

no-smoke conditions. To enable the baseline

measurement, pull TEST from VSS to VBST

again and return to VSS. Once the chamber is

clear, pulse FEED low to high to make the

baseline measurement.

After limits have been set and baseline LTD

measurement has been made, pulse IO to store

all results in memory. Before this step, no limits

are stored in memory.

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