ZLED7x30 Datasheet

© 2016 Integrated Device Technology, Inc.

15

April 20, 2016

Vin

LX

GND

ZLED7X30

D1

LED

String

(C3)

Rs

L1

C2

0.1µF

DIM1

DIM2

GND/Floating

GND/Floating

C1

≥220µF

110/220 VAC

Switch

Halogen

Electronic

Transformer

D1

D2

D3

D4

Figure 3.3

ZLED7x30 Application Circuit using a Halogen Electronic Transformer to Operate with AC Line Supply

3.2

Thermal Considerations for Application Design

3.2.1

Temperature Effects of Load, Layout, and Component Selection

Do not exceed the package power dissipation limits by driving high load currents or by operating the chip at high

ambient temperatures. Power dissipation also increases if the efficiency of the circuit is low as could result from

selecting the wrong coil or from excessive parasitic output capacitance on the switch output. See the layout

guidelines in section 3.4.

3.2.2

internal regulator disables the drive to the internal power MOSFET output switch. Above this threshold, the MOSFET

on-resistance is low enough for the chip to start to operate; however, if the supply voltage remains below the

specified minimum (8.5V), the duty cycle of the output switch will be high and the ZLED7x30 power dissipation will be

at a maximum. Avoid operating the ZLED7x30 under such conditions to reduce the risk of damage due to exceeding

the maximum die temperature. When driving multiple LEDs, their combined forward voltage drop is typically high

3.3

External Component Selection

Note: Also see section 3.4 for layout guidelines for the following external components.

3.3.1

Sense Resistor Rs

Table 3.1 gives values for Rs under normal operating conditions in the typical application shown in Figure 3.1. These

values assume that no dimming condition is valid. Under the conditions given the table, in order to maintain the switch

current below the maximum value specified in section 1

, 0.082Ω is the minimum value for Rs for the ZLED7030, 0.1Ω

for the ZLED7330, 0.13

Ω for the ZLED7530 and 0.27Ω for the ZLED7730.