LD5805 datasheet(13/18 Pages) LEADTREND

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LD5805

06/15/2015

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5805-DS-01 June 2015

Where: D is PWM duty cycle value. RLPF is optional

resistor to keep LPF pin voltage low under IC disable

condition.

Short LED protection

The voltage of LED1 ~ LED4 pins exceeds a typical

threshold of approximately 8.8V during of normal

operation, the corresponding string be turned off and

latched.

Suggest to check LED1~LED4 pins voltage is under

90% of VLSCP value at input voltage is maximum and

LED string voltage is minimum condition. To avoid IC is

latched risk by short LED protection at enable moment.

LED Open String Protection

When any one of the LED strings is open, the output

voltage will boost up until the voltage of OVP reaches

the threshold of 2.0V approximately. The IC will ignore

the opened string and the others will remain operation. If

all the strings are opened and the voltage at OVP

reaches 2.0V, the MOSFET drive output will be turned

off and the IC will shut off and stay latched. Toggle ENA

to resume the operation.

MOSFET Over-Current Protection

The LD5805 provides cycle-by-cycle current limit to

protect the MOSFET. During the MOSFET turning on,

LD5805 detects the CS pin voltage and if inductor peak

current to cause to VCS rises above approximately 0.55V,

the LDR will shut off.

Output Terminal Short-circuit to ground

Protection

When output terminal is short circuit to ground then OVP

voltage falls below about 0.1V, MOSFET driving output

(LDR pin) will turn off. This will protect the converter

from damage.

LED1-3 Channels Operation

For applications where only three LED strings are used,

the LD5805 provides design flexibly by disabling the

fourth channel, LED4 opened. It is required that a

resistor (RSET) connected between CS pin and Boost

MOS Source pin. The three LED strings should be

connected to LED1-3 correspondingly.

LED String Setting

RSET

1~3 Channel

4.7KΩ

1~4 Channel

100RΩ

Multi-Chip Parallel Operation

The LD5805 is flexible for extending LED Channels with

two or three LD5805s in parallel. For the connection of

two LD5805s extending 8 strings LEDs (Max.2 ICs):

(1) Connector the VIN pins of the master IC and the

slave IC together to provide the power of the slave

IC internal logic circuitry.

(2) Connector the COMP pins of the slave IC and the

master IC together to regulate the voltage of all 8

strings LEDs.

(3) The MOS driving signals of the slave IC are not

used; the boost converter can be only driven by the

master IC.

(4) Do not let the CS pin of the slave IC floating,

connector it to GND.

(5) The EN and Dimming signals should be applied to

both ICs.

It is recommended to use external PWM dimming mode

to achieve the accurate dimming synchronization of both

parts.

Loop compensation

The LD5805 has an internal trans-conductance error

amplifier for LED current regulation for COMP output to

compensate the control loop. In case of open LED event

that all LED strings are open, the COMP node will

compensate the control loop still. The external inductor,

output capacitor, the compensation resistor and the

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