XRP7613IDBTR-F Datasheet, PDF (10/14 Pages) Exar Corporation – 1.2A 36V Step Down High Brightness LED Driver

XRP7613
1.2A 36V Step Down High Brightness LED Driver
PROTECTIONS
LED Open Circuit Protection
Upon detection of an open-circuit on any LED
connected to the XRP7613, the device will shut
down.
LED Short Circuit Protection
Upon detecting a short-circuit on any LED
connected to the XRP7613, the device will
maintain the LED current as set by the
external sense resistor R_SET.
UVLO Protection
The XRP7613 has an Under Voltage Lock-Out
comparator to monitor the Input Voltage V_IN.
The V_IN UVLO threshold is set internally: when
V_IN pin is greater than 6.0V the XRP7613 is
permitted to start up pending the removal of
all other faults.
LED Thermal Protection
The XRP7613 includes a LED thermal
regulation circuit to prevent an over
temperature situation on the LED. When the
LED temperature rises above a predefined
threshold, the XRP7613 will reduce linearly the
LED current from its nominal set value.
Fig. 21: VTH Voltage
The XRP7613 continuously monitors the LED
temperature by measuring the voltage on its
TH pin. The V_TH voltage is created through a
resistive network of a negative temperature
coefficient (NTC) thermistor R_TH and a fixed
resistor R_T between VREF pin and ground.
By setting R_T=10KΩ and using a 103KT1608
thermistor, the voltage on the TH pin will
reduce to 0.4V when the LED temperature
reaches 70°C. The LED average current will be
decreased linearly when V_TH is between 0.4V
and 0.28V. If the LED temperature is over
90°C, the voltage on the TH pin will reduce to
0.28V and the LED will be turned off in order
to decrease the LED temperature. When the
voltage on the TH pin rises to 0.3V, the LED
will be turned on again.
If the LED thermal regulation function isn’t
required, the TH pin should be connected
directly to VREF pin to disable this function.
DIODE SELECTION
Schottky diodes, with their low forward
voltage drop and fast reverse recovery, are
the ideal choices for any XRP7613
applications. The forward voltage drop of a
Schottky diode represents the conduction
losses in the diode, while the diode
capacitance (CT or CD) represents the
switching losses. For diode selection, both
forward voltage drop and diode capacitance
need to be considered. Schottky diodes with
higher current ratings usually have lower
forward voltage drop and larger diode
capacitance, which can cause significant
switching losses. A Schottky diode with a 2A
current rating is adequate for most XRP7613
applications.
INPUT CAPACITOR SELECTION
Ceramic capacitors with their low ESR values
and small size are ideal for the XRP7613
applications. When selecting an input
capacitor, a low ESR capacitor is required to
minimize the noise at the device input. It may
be necessary to add an extra small value
ceramic type capacitor in parallel with the
input capacitor to prevent any possible
ringing.
INDUCTOR SELECTION
Recommended inductor values for the
XRP7613 are in the range of 22µH to 68 µH.
The inductor selected should have low core
losses and low DCR.
© 2012 Exar Corporation
10/13
Rev. 1.2.0