ZLED7x30 Datasheet

© 2016 Integrated Device Technology, Inc.

16

April 20, 2016

)

(

*

*

LX

L

S

AVG

LED

IN

ON

R

r

R

I

V

V

I

L

t

+

+

−

−

∆

=

)

(

*

*

L

S

AVG

D

LED

OFF

r

R

I

V

V

I

L

t

+

+

+

∆

=

To ensure stable output current, use a 1% accuracy resistor with adequate power tolerance and a good temperature

characteristic for Rs.

Table 3.1

Recommended Values for Sense Resistor Rs

Nominal Average Output Current (mA)

(Ω)

1200 (maximum for ZLED7030)

0.082

1000 (maximum for ZLED7330)

0.1

750 (maximum for ZLED7530)

0.13

667

0.15

350 (maximum for ZLED7730)

0.27

333

0.3

3.3.2

Inductor L1

The recommended range for the L1 inductor is 33

μH to 220μH. Select the inductor value for L1 as needed to ensure

that switch on/off times are optimized across the load current and supply voltage ranges. If the application requires a

high supply voltage and low output current, inductance values at the high end of this range are recommended to

minimize errors due to switching delays, which can reduce efficiency and increase ripple on the output. Also see

(3)

(4)

Where:

Symbol

Description

L

L1 coil inductance in H

ΔI

L1 coil peak-peak ripple current in A (internally set to 0.3

∗ I

Supply voltage in V

Total forward voltage in V for LED string

Nominal average LED current in A

Rs

External current sense resisto

r in Ω

L1 coil resistance in Ω

LX switch resistance in Ω

D1 diode forward voltage at the required load current in V