ISL29038
0x04[4]) is set and then clear the flag by writing ‘0’ to Reg
0x04[4].
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.
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.
Typical Application Circuit
A typical application circuit for the ISL29038 is shown in
2
Power-Down
Figure 12. The ISL29038’s I C address is internally hard wired as
‘1000100x’, with x representing the R/W bit. The device can be
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.
2
2
connected to a system’s I C bus together with other I C
compliant devices. It is important to ensure that there is no
2
address conflict with other I C 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 I C devices on the
bus.
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.
2
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
ALS Data Count Read Out
2
st
A 2 byte I C read from ALS_DATA_HB outputs MSB 1 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.
separate power supplies. The V IRLED can range from 2.25V to
DD
5.0V and the V _ANALOG can range from 2.25V to 3.63V. In
DD
dual supply configuration, resistor R should not be installed.
2
In single supply configuration, the IR LED and the ISL29038 are
Proximity Detection of Various Objects
powered from the same power source. The V _IRLED can range
from 2.25V to 3.63V and the V _Analog is derived from
DD
DD
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.
V
_IRLED using resistor R .
DD
2
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_PULLUP
VDD_IRLED
SCL, SDA AND
INT PULLUPs
D
IRLED
IRDR
INT
SDA
SCL
1
R
100
C
1µF
2
1
U1
SMBus MASTER
1
2
3
4
8
7
6
5
GNDIR
AVDD
AGND
RExt
INT
SDA
SCL
VDD_ANALOG
C
2
1µF
ISL29038
R
1
499k
R : 499k 1% RESISTOR
1
R : 100Ω 5% RESISTOR
2
C , C : 1µF CERAMIC 10V CAPACITOR
1
2
D : OSRAM SFH4650 INFRARED LED
1
FIGURE 12. TYPICAL APPLICATIONS CIRCUIT
FN7851.0
October 12, 2012
12
XICOR [ XICOR INC. ]
