CL6807 查看數據表（PDF） - Unspecified

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CL6807

30V 1A LED driver with internal switch

Unspecified 

CHIPLINK

SEMICONDUCTOR

CL6807

LED current.

The ADJ pin can be driven by an external dc voltage(VADJ) to adjust the output current to a value

belowthe nominal average value defined by RS.

High luminance LEDs often need to be supplied with atemperature compensated current in

order to maintainstable and reliable operation at all drive levels. The LEDs are usually mounted

remotely from the device so,for this reason, the temperature coefficients of theinternal circuits for

the CL6807 have been optimized tominimize the change in output current when nocompensation is

employed. If output currentcompensation is required, it is possible to use anexternal temperature

sensing network - normally using Negative Temperature Coefficient (NTC) thermistors and/or

diodes, mounted very close to the LED(s). Theoutput of the sensing network can be used to drive

the ADJ pin in order to reduce output current with increasing temperature.

Undervoltage Lockout (UVLO)

The CL6807 include a 7V undervoltage lockout (UVLO) with 500mV hysteresis. When VIN falls

below 7V, turning off the internal n-channel MOSFET. MOSFET is on once VIN is 7.5V or higher.

5V Regulator

VCC is the output of a 5V regulator capable of sourcing 10mA. VCC was bypassed to GND with

internal capacitor.

ADJ Input

The CL6807 allow dimming with a PWM signal at the ADJ input. A logic level below 0.5V at ADJ

turns off the LED current. To turn the LED current on, the logic level at ADJ must be at least 2.5V.

APPLICATION DESCRIPTION

Selecting RSENSE to Set the LED Current

The CL6807 feature a programmable LED current using a resistor connected between VIN and

ISNS. Use the following equation to calculate the sense resistor:

I out

=

0.1 × V ADJ

2.5 × Rs

(0.5V

≤ V ADJ

≤ 2.5V )

Current Regulator Operation

The CL6807 regulate the LED output current using an input comparator with hysteresis (Figure

1). As the current through the inductor ramps up and the voltage across the sense resistor reaches

the upper threshold, turns off the internal MOSFET. The MOSFET turns on again when the inductor

current ramps down through the freewheeling diode until the voltage across the sense resistor

equals the lower threshold. Use the following equation to determine the operating frequency:

f sw

=

(VIN

− n × VLED ) × n × VLED

VIN × ΔV × L

× RSENSE

where n = number of LEDs, VLED = forward voltage drop of one LED, and ΔV = (VSNS_HI -

VSNS_LO).

2008-09-09

5

http://www.chiplink-semi.com

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