TMG3992 datasheet(26/96 Pages) OSRAM

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ams Datasheet

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[v1-06] 2018-Feb-27

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TMG3992 − Detailed Description

Proximity results are affected by three fundamental factors: IR

LED emission, IR reception, and environmental factors,

including target distance and surface reflectivity.

The IR reception signal path begins with IR detection from four

[directional gesture] photodiodes and ends with the 8-bit

proximity result in PDATA register. Signal from the photodiodes

is combined, amplified, and offset adjusted to optimize

performance. The same four photodiodes are used for gesture

operation as well as proximity operation. Diodes are paired to

form two signal paths: North/East and South/West. Regardless

of pairing, any of the photodiodes can be masked to exclude its

contribution to the proximity result. Masking one of the paired

diodes effectively reduces the signal by half and causes the

full-scale result to be reduced from 255 to 127. To correct this

reduction in full-scale, the proximity gain compensation bit,

PCMP, can be set, returning F.S. to 255. Gain is adjustable from

1x to 8x using the PGAIN control bits. Offset correction or

cross-talk compensation is accomplished by adjustment to the

POFFSET_NE and POFSET_SW registers. The analog circuitry of

the device applies the offset value as a subtraction to the signal

accumulation; therefore a positive offset value has the effect of

decreasing the results.

Optically, the IR emission appears as a pulse train. The number

of pulses is set by the PPULSE bits and the period of each pulse

is adjustable using the PPLEN bits. The intensity of the IR

emission is selectable using the LDRIVE control bits. These bits

correspond to four factory calibrated current levels. If a higher

intensity is required (E.g. longer detection distance or device

placement beneath dark glass) then the LEDBOOST bits can be

used to increase LDR current 150%, 200%, or 300% of LDRIVE

setting.

LED duty cycle and subsequent power consumption of the

integrated IR LED can be calculated using the following table

shown in Figure 31, and equations. If proximity events are

separated by a wait time, as set by AWAIT and WLONG, then the

total LED OFF time must be increased by the wait time.

Figure 31:

Approximate Proximity Timing

PPLEN

tINIT (µs)

tLED ON (µs)

tACC (µs)

tCNVT (µs)

µs

40.8

5.4

28.6

796.6

µs

44.9

9.5

36.73

796.6

µs

53.0

17.7

53.1

796.6

µs

69.4

34.0

85.7

796.6

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