NCP5007SNT1 View Datasheet(PDF) - ON Semiconductor

Part Name

Description

MFG CO.

NCP5007SNT1

Compact Backlight LED Boost Driver

ON Semiconductor 

NCP5007

TYPICAL APPLICATIONS CIRCUITS

Standard Feedback

The standard feedback provides constant current to the

LEDs, independently of the Vbat supply and number of

Vbat

LEDs in series. Figure 28 depicts a typical application to

supply 13 mA to the load.

Vbat

GND

U1

3 EN

5

Vbat

GND

2 GND

1 FB

Vout 4

NCP5007

C1

4.7 mF

L1

22 mH

D1

GND

MBR0530

C2

1.0 mF

R1

15 W

D6 D5 D4 D3 D2

LED LED LED LED LED

GND

Figure 28. Basic DC Current Mode Operation with

Analog Feedback

PWM Operation

The analog feedback pin 1 provides a way to dim the LED

by means of an external PWM signal as depicted in

Figure 29. Taking advantage of the high internal impedance

presented by the FB pin, one can set up a simple R/C network

to accommodate such a dimming function. Two modes of

operation can be considered:

• Pulsed mode, with no filtering

• Averaged mode with filtering capacitor

Although the pulsed mode will provide a good dimming

function, it will yield high switching transients which are

difficult to filter out in the control loop. As such this first

approach is not recommended. The output current depends

upon the duty cycle of the signal presented to the node pin 1:

this is very similar to the digital control shown in Figure 30.

The average mode yields a noise−free operation since the

converter operates continuously, together with a very good

dimming function. The cost is an extra resistor and one extra

capacitor, both being low cost parts.

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