ISL29038_15 Datasheet, PDF (12/15 Pages) Intersil Corporation – Low Power Ambient Light and Proximity Sensor with Enhanced Infrared Rejection

ISL29038
(Reg 0x04[4]) is set and then clear the flag by writing ‘0’ to Reg
0x04[4].
Following power-up, a ‘Brown-Out’ condition, if detected, is
reported by PWR_FAIL flag by Reg 0x04[4]. Device configuration
registers are not set to their power-up default after ‘Brown-Out’.
PWR_FAIL flag should be periodically monitored to detect post
power-up power supply interruption.
Power-Down
Setting ALS_EN (Reg 0x02[2]) and PROX_EN (Reg 0x01[5]) to ‘0’
puts the ISL29038 into a power-down state with power supply
current dropping to less than 1µA. All configuration registers are
maintained in power-down mode.
Soft Reset
A software reset to ISL29038 can be initiated by writing 0x38 to
Reg 0x0E. Following reset, all configuration registers are set to
their default power-up state. After soft reset, the ISL29038
defaults to the power-down configuration.
ALS Data Count Read Out
A 2 byte I²C read from ALS_DATA_HB outputs MSB 1^st data on
SDA. This data is LSB justified with a zero fill for unused bits.
NOTE: That the MSB byte address precedes the LSB byte address. The
ALS count is 256*(ALS_DATA_HB) + ALS_DATA_LB.
Proximity Detection of Various Objects
Proximity sensing relies on the amount of IR reflected back from
objects. A perfect black object would absorb all incident light and
reflect no photons. The ISL29038 is sensitive enough to detect
black ESD foam, which reflects only 1% of IR. Blonde hair typically
reflects more than brown hair and skin tissue is more reflective
than human hair.
IR penetrates into the skin and is reflected from within. As a
result, the proximity count generally peaks at contact and
monotonically decreases as skin moves away. The reflective
characteristics of skin are very different from that of a inanimate
object such as paper.
Typical Application Circuit
A typical application circuit for the ISL29038 is shown in
Figure 12. The ISL29038’s I²C address is internally hard wired as
‘1000100x’, with x representing the R/W bit. The device can be
connected to a system’s I²C bus together with other I²C
compliant devices. It is important to ensure that there is no
address conflict with other I²C devices on the bus.
The SCL, SDA and INT pins on ISL29038 are open drain and
require pull-up resistors for proper system operation. Values of
the pull-up resistors is system dependent and can range from
2.2k to 10k depending upon the number of I²C devices on the
bus.
The proximity sensing system can be powered using a dual power
supply or using a single power supply. In dual supply
configuration, the IR LED and the ISL29038 are powered from
separate power supplies. The V_DD IRLED can range from 2.25V to
5.0V and the V_DD_ANALOG can range from 2.25V to 3.63V. In
dual supply configuration, resistor R₂ should not be installed.
In single supply configuration, the IR LED and the ISL29038 are
powered from the same power source. The V_DD_IRLED can range
from 2.25V to 3.63V and the V_DD_Analog is derived from
V_DD_IRLED using resistor R₂.
In either power supply configuration, a 1µF decoupling capacitor
should be installed close to the AVDD pin, and another 1µF
decoupling capacitor should be placed close to the IR LED anode.
VDD_IRLED
VDD_ANALOG
R₂
100
C₂
1µF
VDD_PULLUP
C₁
D₁ IRLED
1µF
1
2
3
4
U1
GNDIR
AVDD
AGND
RExt
IRDR
INT
SDA
SCL
8
7
6
5
R₁ ^ISL29038
499k
SCL, SDA AND
INT PULL UPs
SMBus MASTER
INT
SDA
SCL
R₁: 499k 1% RESISTOR
R₂: 100Ω 5% RESISTOR
C₁, C₂: 1µF CERAMIC 10V CAPACITOR
D₁: OSRAM SFH4650 INFRARED LED
FIGURE 12. TYPICAL APPLICATIONS CIRCUIT
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FN7851.1
January 23, 2015