Datasheet

ADPD1080/ADPD1081 Data Sheet
Rev. B | Page 52 of 74
the photodiode causes the integrator to increase with the
negative going output signal from the TIA.
The LED flashes in the second and third pulses of the four pulse
sequence. Setting Register 0x58, Bits[6:5] = 2 and Register 0x58,
Bits[11:10] = 1 forces the device to add the second and third
pulses while subtracting the first and fourth pulses, effectively
cancelling out the ambient light and electrical offsets and drift.
A comparison of float ambient mode vs. float LED mode is
shown in Table 33 and Table 34.
PRECONDITION
LED PULSES
REGISTER 0x5A, BITS[15:12] = 0x9
MASK PULSES 1 AND 4
FLASH PULSES 2 AND 3
ACCUMULATED
CHARGE ON PD
INTEGRATOR
OUTPUT
INTEGRATOR
SEQUENCE
INTEGRATOR
RESET
ADC READ
t = 0
t = 16µs, REGISTER 0x59, BITS[12:8] = 0x10
PRECONDITIONING TIME
t = 26.75µs, REGISTER 0x3B, BITS[10:0] = 0x238
START OF INTEGRATION TIME
t = 30µs, REGISTER 0x35, BITS[7:0] = 0x1E
TIME OF FIRST CHARGE DUMP
MASKED LED PULSE
t = 17µs, REGISTER 0x3F, BITS[7:0] = 0x11
LED PULSE OFFSET
REGISTER 0x3F, BITS[12:8] = 0xC
LED PW = 12µs
REGISTER 0x36, BITS[7:0] = 0x10
FLOAT PERIOD = 16µs
REGISTER 0x3B,
BITS[15:11] = 0x3
INTEGRATION TIME = 3µs
MASKED LED PULSE
REGISTER 0x35, BITS[12:8] = 0x2
CHARGE DUMPTIME = 2µs
FLASH LED FLASH LED
16110-053
CONNECT/FLOAT
Figure 55. Example Timing Diagram of Four Pulse Float LED Mode Sequence
Table 33. Float Ambient Mode—Measure Ambient Light Level
Pulse Float Time Integrated Charge Calculation Result
1 Shorter Offset, Ambient 1 (shorter time) Subtract Ambient Measurement = Ambient 2 – Ambient 1 (Offset Cancels)
2 Longer Offset, Ambient 1 (shorter time) Add
3 Not applicable Not applicable Not applicable
4 Not applicable Not applicable Not applicable
Table 34. Float LED Mode—Measurement Synchronous Reflected Light from LED
Pulse Float Time Integrated Charge Calculation Result
1 Equal Offset + Ambient Subtract Sync LED Response = Reflected LED Return (Offset and Ambient Cancels
2 Equal Offset + Ambient + LED Add
3 Equal Offset + Ambient + LED Add
4 Equal Offset + Ambient Subtract
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