RT4532WSC datasheet(10/12 Pages) RICHTEK

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RT4532

www.richtek.com

DS4532-01 August 2015

is a registered trademark of Richtek Technology Corporation.

Application Information

LED Short Protection

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.

Soft-Start

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.

OCP Protection

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.

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.

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.

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

LED

LED, Full

Code

255



Where

ILED, Full : the full-scale LED current set by Reg0x02 <3>.

Code : the 8bit brightness code Reg0x04 <7:0>

programmed by I2C interface.

PWM Brightness Dimming

Besides programmable built-in I2C backlight LED current

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.

Inductor Selection

The recommended inductor value for dual-channel 6

WLEDs applications is 10

μH. 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 low DCR for better efficiency.

Capacitor Selection

μF 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.

threshold, the device is shut down. If the input voltage

rises by under-voltage lockout hysteresis (200mV typical),

the IC restarts.

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.

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