AN1910: Enhancing RGB Sensitivity and Conversion Time

Application Note 1910
Enhancing RGB Sensitivity and Conversion Time
Introduction
ISL29125
TOP VIEW
The RGB sensor is a low power, high sensitivity, RED, GREEN,
and BLUE color light sensor (RGB) with an I2C (SMBus
compatible) interface. Its state of the-art photodiode array
provides an accurate RGB spectral response and excellent light
source to light source variation (LS2LS). The sensor is designed
to reject IR in light sources allowing the device to operate in
environments from sunlight to dark rooms. The integrating
ADC rejects 50Hz and 60Hz flicker caused by artificial light
sources. Selectable ranges allow the user to optimize
sensitivity suitable for the specific application. The sensor has
2 sensitivity ranges such as range 0 from 5.7 mlux to 375 lux
and Range 1 from 0.125 lux to 10,000 lux. However, Intersil
has options which can expose even higher sensitivity by simple
setting in custom registers.
VDD
1
6
SCL
NC
2
5
INT
GND
3
4
SDA
ISL29124
TOP VIEW
GND
1
4
VDD
SDA
2
3
SCL
Related Literature
ISL29125 datasheet
TABLE 1. EXPOSE THE CUSTOM REGISTER
REGISTER
ADDRESS
NAME
REGISTER BITS
DEC
HEX
B7
B6
B5
B4
B3
B2
B1
B0
Device ID
0
0x00
0
1
1
1
1
1
0
1
7Dh
RO
CUSTOM MODE
ACCESS
0
0x00
X
X
X
X
X
X
X
X
N/A
WO
REGISTER 0x02
2
0x02
00h
RW
STATUS
8
0x08
TMEN
REVEN
See Datasheet for more detail
04h
RO
CUSTOM MODE 1
25
0x19
RESERVED
SENS_EN
RESERVED
00h
RW
CUSTOM MODE 2
26
0x1A
00h
RW
CUSTOM MODE 3
27
0x1B
00h
RW
CUSTOM MODE 4
28
0x1C
00h
RW
CUSTOM MODE 5
29
0x1D
Set by
Intersil
RO
May 6, 2014
AN1910.1
See Datasheet for more detail
RESERVED
FAST
RESERVED
Gain Setting
RESERVED
SENSX[1]
Gain Setting
1
SENSX[0]
DEFAULT ACCESS
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas LLC 2014. All Rights Reserved
Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
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Application Note 1910
Register 0x00
Register 0x00 performs two functions. If Reg 0x00 is in READ
ONLY mode then it will be a Device ID. When the register is in the
WRITE ONLY mode it will open up access to CUSTOM MODE
registers.
To access into a CUSTOM MODE, write 89h then C9h into
Register 0x00.
To reset all Registers to default and/or all state machine by
writing 46h into Reg 0x00.
TABLE 2. DEVICE ID/ CUSTOM ACCESS
REGISTER
ADDRESS
NAME
REGISTER
BITS
REGISTER BITS
DEC
HEX
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT ACCESS
Device ID
0
0x00
0
1
1
1
1
1
0
1
7Dh
RO
CUSTOM MODE
ACCESS
0
0x00
X
X
X
X
X
X
X
X
N/A
WO
Register 0x02
See datasheet for more detail on how to set IR compensation.
Write 00h to Reg 0x02 then Range 0 = 250 lux and range
1 = 6750 lux. Write BFh to Reg 0x02 then Range 0 = 375 lux and
Range 1 = 10,000 lux.
Register 0x08
TABLE 3. STATUS REGISTER (REG0x08)
REGISTER
ADDRESS
REGISTER BITS
NAME
DEC
HEX
B7
B6
B5
STATUS
8
0x08
TMEN
REVEN
RGBCF[1]
B4
B3
B2
RGBCF[0] RESERVED
BOUTF
B1
B0
DEFAULT ACCESS
CONVENF RGBTHF
0x04
RO
RGBTHF [B0]
BOUTF [B2]
This is the status bit of the interrupt. The bit is set to logic high
when the interrupt thresholds have been triggered (out of
threshold window), and logic low when not yet triggered. Once
activated and the interrupt is triggered, the INT pin goes low and
the interrupt status bit goes high until the status bit is polled
through the I2C read command. Both the INT output and the
interrupt status bit are automatically cleared at the end of the
8-bit (00h) command register transfer.
Bit2 on register address 0x08 is a status bit for the brownout
condition (BOUT). The default value of this bit is HIGH, BOUT = 1,
during the initial power-up. This indicates the device may possibly
have gone through a brownout condition. Therefore, the status
bit should be reset to LOW, BOUT = 0, by an I2C write command
during the initial configuration of the device. The default register
value is 0x04 at power-on.
TABLE 4. INTERRUPT FLAG
TABLE 6. BROWNOUT FLAG
B0
OPERATION
B2
OPERATION
0
Interrupt is cleared or not triggered yet
0
No Brownout
1
Interrupt is triggered
1
Power-down or Brownout occurred
RGBCF [B5:B4]
CONVENF [B1]
This is the status bit of conversion. The bit is set to logic high
when the conversion have been completed, and logic low when
the conversion is not completed or not converted.
TABLE 5. CONVERSION FLAG
B1
OPERATION
B[5:4] are flag bits to display7.
TABLE 7. CONVERSION FLAG
B5:4
RGB UNDER CONVERSION
00
No Operation
0
Still convert or cleared
01
GREEN
1
Conversion completed
10
RED
11
BLUE
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AN1910.1
May 6, 2014
Application Note 1910
REVEN [B6]
TMEN[B7]
REVEN is Bit 6 of the status register. The bit is asserted to logic 1
when writing 89h to reg 0x00. By default this bit is logic low.
TMEN is Bit 7 of the status bit of Custom Mode condition. The bit
is asserted to logic 1 when writing C9h to reg 0x00 and REVEN is
at logic 1. By default it is at logic low.
TABLE 8.
TABLE 9.
B6
OPERATION
B7
0
Logic low or not writing 89h to Reg 0x00
1
Writing 89h to Reg 0x00
OPERATION
0
Logic low or not writing C9h to Reg 0x00 and
REVEN = 0
1
Writing C9h to reg 0x00 and REVEN = 1
B7 and B6 are indicated whether the RGB sensor is in the custom
mode or not.
Register 0x19
SENS_EN is Bit 6 of CUSTOM MODE 1. In order to enable the
CUSTOM MODE 4, SENS_EN should be asserted to a logic high.
By default, it is a logic low or not enable CUSTOM MODE 4.
TABLE 10.
B6
OPERATION
0
Not Enable
1
Access to CUSTOM MODE 4
TABLE 11. CUSTOM MODE 1 (REG 0x19)
REGISTER
ADDRESS
REGISTER BITS
NAME
DEC
HEX
CUSTOM
MODE 1
25
0x19
B7
B6
B5
B4
RESERVED SENS_EN
B3
B2
B1
B0
RESERVED
DEFAULT ACCESS
00h
RW
Register 0x1A
TABLE 12. CUSTOM MODE 2 (REG 0x1A)
REGISTER
ADDRESS
REGISTER BITS
NAME
DEC
HEX
CUSTOM
MODE 2
26
0x1A
B7
B6
B5
RESERVED
B4
B3
B2
FAST
B1
B0
RESERVED
DEFAULT ACCESS
00h
RW
FAST [2]
Bit 2 in Reg 0x1A is asserted to a logic high then ADC clock
frequency is 4x faster than normal mode. By default FAST bit is
set to low for normal mode.
TABLE 13.
B2
OPERATION
0
Normal conversion time
1
4x faster than normal conversion time
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Application Note 1910
Register 0x1B and 0x1D
TABLE 14. CUSTOM MODES 3 AND 5 (REG 0x1B AND REG 0x1D)
REGISTER
ADDRESS
REGISTER BITS
NAME
DEC
HEX
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT ACCESS
CUSTOM
MODE 3
27
0x1B
GAIN SETTING
00h
RW
CUSTOM
MODE 5
29
0x1D
GAIN SETTING
Set by
Intersil
RO
Both CUSTOM MODE 3 and CUSTOM MODE 5 are set by Intersil in
order to have a better part-to-part variation performance.
Register 0x1C
TABLE 15. CUSTOM MODE 4 (REG 0x1C)
REGISTER
ADDRESS
REGISTER BITS
NAME
DEC
HEX
B7
TEST MODE 4
28
0x1C
B6
B5
B4
B3
B2
RESERVED
SENX[1:0]
The full-scale range can be extended to be a high sensitivity at
Bit[1:0] of reg0x1C. The range determines the ADC resolution
(12 bits, and 16 bits). Each selectable range at SENX has a
maximum allowable lux value. More information will be
discussed in the following section.
TABLE 16.
B1:0
HIGH SENSITIVITY RANGES
00
1X
01
1.5X
10
2X
11
2.5X
B0
DEFAULT ACCESS
SENX[1]
SENX[0]
00h
RW
8. To get out of CUSTOM MODE without resetting the device,
write any hex values other than 89h and C9 to Reg 0x00. OR
9. To get out of CUSTOM MODE and reset the device, write 46h
to Reg 0x00. This will reset all registers to their default states.
TABLE 17. SENSITIVITY RANGES
Register
0x02
Write 00h to Register 0x02 Write BFh to Register 0x02
Range 0 = 250 lux,
Range 1 = 6750 lux
Range 0 = 375 lux,
Range 1 = 10,000 lux
Register
0x1C [1:0]
SENX[1:0]
High
Sensitivity
Range (Lux)
SENX[1:0]
High
Sensitivity
Range (Lux)
RANGE 0
00
250
00
375
Application Information
In order to expose high sensitivity ranges and speed up its
conversion time, the sensor needs to be in the custom mode,
instructed in the following steps:
B1
RANGE 1
1. Write 89h to Reg 0x00
01
165
01
250
10
125
10
187.5
11
100
11
150
00
6750
00
10,000
01
6750
01
10,000
10
6750
10
10,000
11
6750
11
10,000
2. Write C9h to Reg 0x00 to enter CUSTOM mode. If user want to
check flag status at bit [7] and bit [6] of Reg0x08 should be
asserted to logic. If they are asserted logic 1 then the sensor
is in the CUSTOM mode.
Reg0x01 [4]
(Bit)
16-bit ADC (Bit[4] = 0)
12-bit ADC (Bit[4] = 1)
3. Read reg 0x1D then store that value in a temp variable
(software GUI/driver).
Reg0x1A [2]
(FAST bit)
FAST= 0
FAST = 1
FAST =0
FAST = 1
4. Write 40h to Reg 0x19 to enable high sensitivity ranges
(Reg 0x1C/ CUSTOM MODE 4).
Conversion
time (ms)
100
25
6.25
1.56
5. Write temp variable at step 2 to reg 0x1B.
Number of
Clocks
6. Table 17 explains multiple higher sensitivity options the
sensor can be:
7. Table 18 explains how the sensor can be sped up in the
conversion time for 16-bit and 12-bit ADC.
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TABLE 18. SPEED-UP CONVERSION TIME
ADC clock
Period (µs)
65536
1.52
4096
0.38
1.52
0.38
AN1910.1
May 6, 2014
Application Note 1910
Block Diagram for High Sensitivity Control Logic
Initialization (1 time only)
ROM
0x1D:Gain Setting
Set CUSTOM Mode Enable
0x1B:CUSTOM MODE 3
0x19:(6):Enable High Sensitivity
W:0x00:0x89
W:0x00:0xC9
Read Value
R:0x1D  MEM
Enable High Sensitivity
W:0x19:0x40
Write Value
W:0x1B:MEM
Exit CUSTOM Mode
W:0x00:0x00
Run Time
R
W:0x00:0x00
S
W:0x00:0xC9
W:0x00:0x89
R
Q
CUSTOM MODE
Enable
Set CUSTOM Mode Enable
W:0x00:0x89
W:0x00:0xC9
Set High Sensitivity
W:0x1C:0x03*ON
Exit CUSTOM Mode
W:0x00:0x00
Q
S
FIGURE 2. INITIALIZATION AND RUNNING TIME
FIGURE 1. HIGH SENSITIVITY CONTROL LOGIC DIAGRAM
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is
cautioned to verify that the document is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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