FP7176

This datasheet contains new product information.

Feeling Technology reserves the rights to modify the product specification without notice.

No liability is assumed as a result of the use of this product. No rights under any patent accompany the sales of the product.

Rev. 0.64

8/14

OFF Timer

The timing resistor connected to RT determines the off-time of the gate driver, and it must be

wired to GND. The equation governing the off-time of the GATE output is given by:

3

.

0

+

25

)

(k

Ω

R

s)=

μ

(

T

T

OFF

within the range of 30k

Ω≦RT(kΩ)≦1MΩ

Average Current Control

The LED current is detected using a sense resistor at the CS pin. The feedback operates in a fast

current is programmed simply as:

)

Ω

(

R

V

277

.

0

=

)

A

(

I

CS

LED

Otherwise:

)

Ω

(

R

185

.

0

×

)

V

(

V

=

)

A

(

I

CS

LD

LED

CS

LED

Current

Average Current =

0.277V

0.277V

t

t

The above equations are only valid for continuous conduction of the output inductor. It is a good

practice to design the inductor such that the switching ripple current in it is 30~40% of its average

peak-to-peak, full load, DC current. Hence, the recommended inductance can be calculated as:

LED

OFF

)

MAX

(

LED

I

×

4

.

0

T

×

V

L=

GATE Output

The GATE output of the FP7176 is used to drive an external MOSFET. It is recommended that

the gate charge QG of the external MOSFET be less than 25nC for switching frequencies ≤100kHz and

less than 15nC for switching frequencies >100kHz.