ISL29147_15 Datasheet, PDF (12/15 Pages) Intersil Corporation – Low Power Ambient Light and Proximity Sensor with Enhanced Infrared Rejection

ISL29147
Power-Up and ‘Brown-Out’ Reset
The ISL29147 has an enhanced power-on-reset system. A
‘Brown-Out’ detector flag in Reg 0x04[4] informs the system that
the device has powered-up properly. This flag should be reset as
part of the initialization sequence.
A ‘Brown-Out’ condition is defined as an operating condition
when the power supply voltage is not within the specified limits.
To prevent this condition we recommend the power supply slew
rate to be greater than 0.5 V/ms.
During the brown-out period at power-up, the I²C interface and
the IR LED driver are inactive. Following brown-out, the I²C
interface is reinitialized and the configuration registers are set to
power-up default values. After power-up and during device
initialization, host should examine that the PWR_FAIL flag
(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 ISL29147 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 ISL29147 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 ISL29147
defaults to the power-down configuration.
ALS Data Count Read Out
A two 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: 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
The 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 ISL29147 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 an inanimate object such as
paper.
Typical Application Circuit
A typical application circuit for the ISL29147 is shown in
Figure 11. The ISL29147’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 the ISL29147 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 ISL29147 are powered from
separate power supplies. The V_DD IRLED can range from 2.25V
to 5.0V and the V_DD can range from 2.25V to 3.63V. In dual
supply configuration, resistor R₁ should not be installed.
In single supply configuration, the IR LED and the ISL29147 are
powered from the same power source. The V_DD__IRLED can range
from 2.25V to 3.63V and the V_DD is derived from V_DD__IRLED
using resistor R₁.
In either power supply configuration, a 1µF decoupling capacitor
should be installed close to the VDD pin, and another 1µF
decoupling capacitor should be placed close to the IR LED anode.
V_DD
R₁
C₂
100Ω
1µF
C₁
1µF
VDD_PULLUP
5
6
7
8
V_DD
SCL
GND
LED+
SDA
INT
IRDR
LED-
4
3
2
1
U1
SMBus MASTER
SCL
SDA
INT
R₁: 100Ω 5% RESISTOR
C₁, C₂: 1µF CERAMIC 10V CAPACITOR
FIGURE 11. TYPICAL APPLICATIONS CIRCUIT
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FN8409.3
January 6, 2015