ZLED7001 Datasheet

© 2016 Integrated Device Technology, Inc.

9

April 20, 2016











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+

∗

=

=

1

R

R

R

V

mV

240

~

V

NTC

NTC

REF

LDH

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+

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1

R

R

R

R

15

.

1

V

I

NTC

NTC

S

REF

OUT

A group of modules based on the ZLED7001 can be matched in LED brightness using the linear dimming input

with the PWM dimming feature still available for overall brightness control.

If the LD pin is not used, it must be connected to the PWMD pin, which is internally pulled-up. When the LD pin

voltage drops below 50mV, the GATE output is switched off.

2.8.

Temperature Compensation

ZLED7001 provides thermal protection for the connected LEDs. Applying an NTC thermistor close to the LED

string will enable the temperature compensation of the LED current. Refer to the application circuit on page 1. If

the temperature of the LEDs rises, the resistance of the NTC thermistor decreases until the voltage of the LD pin

falls below 240mV. Then the average current is controlled by the LD pin and the temperature compensation

function starts. The upper threshold to start compensation is given by equation (5):

(5)

Considering the limit for IREF, under all conditions R1 must be selected larger than 2.2k

Ω. Assuming a 30%

inductor current ripple, the temperature compensated continuous current can be computed as shown in

equation (6):

(6)

When the LD pin voltage drops below 50mV (typical), the GATE output is switched off. The transition to dimming

as well as the switch-off is reversible as soon as the respective thresholds are exceeded after the LED assembly

cools. Adding a capacitor C1 from the LD pin to ground will reduce noise on the LD input.

2.9.

Design Example

A common application for an AC-line-powered ZLED7001 is luminants with a string of several LEDs operated by

one driver. For the example, the following constraints are assumed:

Application:

15W LED luminant with 13 HB LEDs in 1 string

AC supply voltage:

VINAC = 230 VAC

Average DC supply voltage:

VINDC

≈ 280 VDC resulting after bridge rectification and filtering with a 10μF

capacitor; power factor correction is not considered.

LED string forward voltage:

ΣV

F = 13*3.3V

≈ 43V

LED string average current:

ILED = 350mA

IC Input Resistor (RIN) and Hold Capacitor (CIN):

For a given 2N60 MOSFET and a maximum expected switching frequency of 100kHz, the IC input current will be

(

)

mA

kHz

nC

mA

f

Q

mA

I

S

G

IN

4

.

1

)

100

9

(

5

.

0

5

.

0

=

⋅

+

=

⋅

+

≈