ZLED7025 datasheet(19/26 Pages) IDT

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ZSLS7025 Datasheet

April 20, 2016

4.3

Application Circuit Layout Requirements

The guidelines in this section are strongly recommended when laying out application circuits. As for all switching

power supplies, especially those providing high current and using high switching frequencies, layout is an important

design step. If the layout is not well-designed, the regulator could show instability as well as EMI problems. For

additional guidelines, refer to the IDT application note PCB Layout Design Guidelines for LED Driver Circuits

available at http://www.IDT.com.

• Wide traces should be used for connection of the high current loop to minimize the EMI and unnecessary loss.

• The external components ground should be connected to the ZSLS7025 ground and should be as short as

possible. It is especially important that the RFB ground to ZSLS7025 ground connection is as short and wide as

possible to have an accurate LED current.

• The capacitors C

IN, CVDD, and COUT should be placed as close as possible to the ZSLS7025 for good filtering. It

is especially important that the COUT output capacitor connection is as short and wide as possible.

• The Q

1 external MOSFET drain is a fast switching node (also applies to Q2 if the PWM is accomplished with a

dimming control MOSFET as described in section 2.6.3). The inductor L1 and Schottky diode D1 should be

placed as close as possible to the drain, and the connection should be kept as short and wide as possible.

Avoid other traces crossing and routing too long in parallel with this node to minimize the noise coupling into

these traces. The feedback pins (i.e., CS, FB, OVP) should be as short as possible and routed away from the

inductor, Schottky diode, and Q1. The feedback pins and feedback network should be shielded with a ground

plane or trace to minimize noise coupling into this circuit.

• The thermal pad on the back of the external MOSFET package must be soldered to the large ground plane for

ideal heat distribution.

4.4

Application Example

This section provides an example of an application design for the ZSLS7025 for the RC-filter PWM application

described in section 2.6.2 and shown again for reference in Figure 4.2.

Design criteria:

VIN = 12 to 24 V

IOUT = 350mA

VOUT = 30 to 40V (9 to 12 LEDs, Vf = 3.3V)

To calculate the worst case parameters, use the minimum input voltage, maximum output voltage, and maximum

output current; i.e., VIN = 12V, IOUT = 350mA, and VOUT

≈ 40V (12 LEDs, Vf = 3.3V).

ZLED7025 Datasheet(PDF) 19 Page - Integrated Device Technology