Preliminary
EUP2520
Current Limit Protection
Application Information
The EUP2520 has current limiting protection to
prevent excessive stress on itself and external
components during overload conditions. The internal
Setting LED Current
The White LED current is set using the following
equation: For main display:
current limit comparator will disable the NMOS power
device at a typical switch peak current limit of 700
mA.
− V
MAIN _ FB
MAIN _ RTN
I
=
LED
---------------(1)
R
FB
Output Over-Voltage Protection
The EUP2520 contains dedicated circuitry for
monitoring the output voltage. In the event that the
primary LED network is disconnected the output will
PWM Dimming
The LED current can be controlled using a PWM signal
on the enable pin with frequencies in the range of 100
Hz to 1 kHz. While EUP2520 LED current can also be
controlled with PWM signal on the PWM pin with
frequencies in the range of 20kHz to 33kHz, and LED
current is linearly proportional to the duty cycle, the
PWM frequency above audible range will minimize
audible noise from the inductor and/or output capacitor
of the boost converter. The maximum LED current
would be achieved with 100% duty cycle on PWM pin.
~
increase and be limited to 23.2V(typ.). There is a 1V
hysteresis associated with this circuitry, which will
turn the NMOS off when the output voltage is at
24.2V(max.) until the output voltage reach
22.5V(typ.) or lower. The 23.5V limit allows the use
of 25V 1
µF ceramic output capacitors creating an
overall small solution for white LED applications.
Under Voltage Protection
The EUP2520 has an UVP comparator to turn the
NMOS power device off in case the input voltage or
battery voltage is too low preventing an on state of the
power device conducting large amounts of current.
Setting SUB Voltage
Sub-display voltage is be set by choosing RSUB1 and RSUB2 as
illustrated in Figure 5. If RSUB1>100K, a 0.1uF bypass
capacitor should be added to improve performance ,VSUB is
calculated as follow:
Reliability and Thermal Shutdown
The EUP2520 has an internal thermal shutdown
function to protect the die from excessive
temperatures. The thermal shutdown trip point is
typically 160˚C, Normal operation resumes when the
temperature drops below 140˚C.
R
+ R
SUB2
SUB1
---------(2)
V
=
∗ V
SUB _ FB
SUB
R
SUB2
Startup
The EUP2520 does not include a power on reset
circuit and relies on external signal to monitor enable
signal. In the event of under voltage condition, the
device enable pin must be brought low until the input
voltage is above the minimum guarantee voltage
(2.7V).
Figure 5.
The above equation to solve for RSUB1
.
The EUP2520 is optimized for 20V at 30mA over the
input voltage range, for higher output current up to
50mA is achieveable with a minimum input of 3.6V. If
lower VSUB is desired, the output current capability
will be higher.
DS2520 Ver0.1 May. 2007
10
EUTECH [ EUTECH MICROELECTRONICS INC ]
