I7110 Datasheet, PDF (11/17 Pages) List of Unclassifed Manufacturers – 300 Mbps LED Drivers

i7110
7000ppm
3500ppm
Figure-12
The current flows out of the RSET1 pin
determine the LED drive current.
The temperature independent LED driving
current is set mainly by RRSET1, while the
temperature dependent current is set mainly by
RRSET2. However RRSET1 and RRSET2 are
not independent.
The RSET2 pin connects to an internal diode in
the IC, which exhibits standard diode behavior
with temperature. As temperature rises, the
voltage on RSET2 drops, the current flows
through diode increases and the LED drive
current increases.
Given the various interdependencies of the drive
current, RRSET1 and RRSET2, the relationship
with temperature compensation is plotted in
Figure-12
Peaking Function
To improve LED ‘turn on’ time an optional
function ‘peaking’ is included in ‘i7110’. If this
is not required, then the pin PEAK should be left
floating. Two external components are required to
implement peaking. As shown in figure-11. When
the LED is turned on, the voltage on peak is
pulled low very rapidly. This voltage transient is
coupled through RPAEK and CPEAK and exerts
a transient current on the LED.
When the LED is turned off, the voltage on
PEAK is pulled high very rapidly. This Voltage
transient is coupled through RPEAK and CPEAK
and exerts a transient current in the opposite
direction on the LED.
The transient current amplitude and RC decay are
calculated approximately by:
Peak current (Amps): VCC / (RPEAK+3.8)
Decay (seconds): CPEAK*(RPEAK+3.8)
Typical value for CPEAK and RPEAK at 3.3V
operation are:
CPEAK = 20 pf
RPEAK = 10 ohm
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