ISL29044A_14 Datasheet, PDF (15/19 Pages) Intersil Corporation – Low Power Ambient Light and Proximity Sensor with Internal IR-LED and Digital Output

ISL29044A
ALS_TH2 and ALS_TH3 Registers (Address:
0x06[B7,B6,B5,B4] and 0X07)
TABLE 19. INTERRUPT THRESHOLD HIGH REGISTER BITS
NAME
Reg.
REGISTER BITS
Addr
DFLT
Access (Hex) B7 B6 B5 B4 B3 B2 B1 B0 (Hex)
ALS_TH2_LSB RW 0x06 TH7 TH6 TH5 TH4
0xF0
ALS_TH3_MSB RW 0x07 TH7 TH6 TH5 TH4 TH3 TH2 TH1 TH0 0xFF
The upper interrupt threshold registers are used to set the upper
trigger point for interrupt generation. If the ALS value crosses
above or is equal to the upper threshold, an interrupt is asserted
on the interrupt pin and the interrupt flag. A nibble RW Register
ALS_TH(0x06[B7,B6,B5,B4]) and an 8-bit RW ALS_TH3(0x07)
provides the low and high bytes, respectively, of the upper
interrupt threshold. The high and low bytes from each set of
registers are combined to form a 12-bit threshold value. The
interrupt threshold registers default to 0xFF on power-up.
Data Registers (Addresses: 0x08)
NAME ACCESS
DATA RO
TABLE 20. ADC REGISTER BITS
REG.
ADDR
(HEX)
Register Bits
DFLT
B7 B6 B5 B4 B3 B2 B1 B0 (Hex)
0x08 D7 D6 D5 D4 D3 D2 D1 D0 0x00
The ISL29044A has 8-bit read-only registers to hold the ADC
value. The registers are refreshed after every conversion cycle.
The default register value is 0x00 at power on.
Data Registers (Addresses: 0x09 and 0x0A)
TABLE 21. ADC REGISTER BITS
Reg. Addr
Register Bits
DFLT
NAME Access (Hex) B7 B6 B5 B4 B3 B2 B1 B0 (Hex)
DATA_LSB RO
DATA_MSB RO
0x09 D7 D6 D5 D4 D3 D2 D1 D0 0x00
0x0A
D11 D10 D9 D8 0x00
The ISL29044A has one 8-bit read-only register to hold the lower,
and one nibble (4-bit read only) to hold the upper of the ADC
value. The nibble (4-bit read only) is accessed at address 0x0A
and the lower byte is accessed at address 0x09. For a 12-bit
resolution, the data is from D0 to D11. The registers are
refreshed after every conversion cycle. The default register value
is 0x00 at power on.
Applications Information
Calculating Lux
The ISL29044A’s ADC output codes are directly proportional to lux
when in ALS mode (see ALSIR_MODE bit).
E_calc = α_RANGE × OUT_ADC
(EQ. 2)
In Equation 2, E_calc is the calculated lux reading and OUT
represents the ADC code. The constant α to plug in is determined
by the range bit ALS_RANGE (register 0x1 bit 1) and is
independent of the light source type.
TABLE 22. ALS SENSITIVITY AT DIFFERENT RANGES
ALS_RANGE
α_RANGE
(Lux/Count)
0
0.0488
1
0.7814
Table 22 shows two different scale factors: one for the low range
(ALS_RANGE = 0) and the other for the high range
(ALS_RANGE = 1).
Noise Rejection
Charge balancing ADC’s have excellent noise-rejection
characteristics for periodic noise sources whose frequency is an
integer multiple of the conversion rate. For instance, a 60Hz AC
unwanted signal’s sum from 0ms to k*16.66ms (k = 1,2...ki) is
zero. Similarly, setting the device’s integration time to be an
integer multiple of the periodic noise signal greatly improves the
light sensor output signal in the presence of noise. Since wall
sockets may output at 60Hz or 50Hz, our integration time is
100ms: the lowest common integer number of cycles for both
frequencies.
Proximity Detection of Various Objects
Proximity sensing relies on the amount of IR reflected back from
objects. A perfectly black object would absorb all light and reflect
no photons. The ISL29044A is sensitive enough to detect black
ESD foam, which reflects only 1% of IR. For biological objects,
blonde hair reflects more than brown hair and customers may
notice that skin tissue is much more reflective than hair. IR
penetrates into the skin and is reflected or scattered back from
within. As a result, the proximity count peaks at contact and
monotonically decreases as skin moves away. The reflective
characteristics of skin are very different from that of paper.
Soldering Considerations
Convection heating is recommended for reflow soldering;
direct-infrared heating is not recommended. The plastic ODFN
package requires a custom reflow soldering profile pursuant to
Figure 4 in TB487 (Surface Mount Assembly Guidelines for
Optical Co-Package Sensor and LED).
15
FN8419.1
April 19, 2013