RT4532
Application Information
LED Short Protection
threshold, the device is shut down. If the input voltage
rises by under-voltage lockout hysteresis (200mV typical),
the IC restarts.
LED short protection prevents abnormal connection to
cause IC damage avoiding FB1/FB2 connecting power
supply. And, If unbalanced LEDs series (cause FB1 or
FB2 > 9.6V) is different between channel1 and channel2,
IC will also occur LED short event. As LED short event
occur more than deglitch time 2ms, IC will shut-down latch
until IC is reset by EN pin.
Linear Brightness Dimming
The chip is built-in an I2C 8-bit resolution brightness control
with maximum 20mA/40mA selection. Reg0x02 <3>
corresponds to full-scale LED current control. Reg0x04
<7:0> sets 8bits resolution brightness dimming control.
Code
Soft-Start
I
=
I
LED, Full
LED
255
The RT4532 includes a soft-start function to avoid high
inrush current during start-up. The soft-start function is
achieved by clamping the output voltage of the error
amplifier with another voltage source that is increased
slowly from zero to near VIN during the soft-start period.
Where
ILED, Full : the full-scale LED current set by Reg0x02 <3>.
Code : the 8bit brightness code Reg0x04 <7:0>
programmed by I2C interface.
OCP Protection
PWM Brightness Dimming
The RT4532 features a 1A current limitation. The current
flowing through the inductor during a charging period is
detected by a current sensing circuit. If the value exceeds
the current limit, the N-MOSFET will be turned off. The
inductor will then be forced to leave charging stage and
enter discharging stage. Therefore, the inductor current
will not increase to reach current limit.
Besides programmable built-in I2C backlight LEDcurrent
control, the RT4532 features a built-in PWM dimming
current control by setting Reg0x02 <6> to 1, offering a
linear current dimming by external clock source. In order
to guarantee the PWM dimming resolution (7 bit at >
15kHz application), recommending dimming frequency
have to be operated at range of 400Hz to 20kHz.
The over-temperature protection function will be latched
at shutdown status when the junction temperature
exceeds 140°C for 2ms.After re-power on sequence, the
converter will automatically resume switching.
Inductor Selection
The recommended inductor value for dual-channel 6
WLEDs applications is 10μH. When selecting the
inductor, the inductor rated saturation current should be
higher than the peak current at maximum load. Small size
and better efficiency are major concerns for portable
devices. The inductor should have low core loss at 1.1MHz
and lowDCR for better efficiency.
OVP Protection
The chip provides over-voltage protection function to limit
the output voltage in abnormal conditions. The OVP
threshold voltage is 24V/16V by selecting Reg0x02 <7>.
Once the LED is open, the output voltage reaches the
OVP threshold, the driver will be shut down.
Capacitor Selection
10μF input ceramic capacitor and 1μF output ceramic
capacitor are recommended for driving dual-channel 6
WLEDs applications. For better voltage filtering, ceramic
capacitors with low ESR are recommended. X5R and X7R
types are suitable because of their wide voltage and
temperature ranges.
Under-Voltage Lockout
An under-voltage lockout circuit prevents the operation of
the device at input voltages below under-voltage threshold
(2.3V maximum). When the input voltage is below the
Copyright 2015 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS4532-01 August 2015
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