ZLED7010 Datasheet

© 2016 Integrated Device Technology, Inc.

9

April 20, 2016

S

OUT

R

mV

95

I

=

2

Circuit Description

The ZLED7010 is an inductive step-down converter for driving LEDs. It operates in continuous mode, enabling

proper LED current control. The ZLED7010 supports linear or PWM control of the LED current. It provides

temperature compensation to maintain stable and reliable operation of the LEDs. Only a few external components

are needed for typical applications.

2.1.

Voltage Supply

The ZLED7010 has an internal regulator that disables the LX output until the voltage supply rises above a start-up

threshold voltage set internally as needed to ensure that the power MOSFET on-resistance is low enough for

proper operation. When the supply voltage exceeds the threshold, the ZLED7010 begins normal operation.

Important: The ZLED7010 must be operated within the operating voltage range specified in section 1.2 to avoid

conditions that could result in thermal damage to the ZLED7010. Operating with the supply voltage below the

minimum can result in a high switch duty cycle and excessive ZLED7010 power dissipation, risking over-

temperature conditions (also see section 4.1 regarding thermal restrictions) which could result in activation of the

ZLED7010’s thermal shut-down circuitry (see section 4.2). With multiple LEDs, the forward drop is typically

adequate to prevent the chip from switching below the minimum voltage supply specification (6V), so there is less

risk of thermal shut-down.

2.2.

ZLED7010 Standby Mode

Whenever the ADJI pin voltage falls below 0.2V, the ZLED7010 turns the output off and the supply current drops

to approximately 60μA. This standby mode minimizes current consumption.

2.3.

Output Current Control

The LED control current output on the LX pin is determined by the value of external components and the control

voltage input at the ADJI pin. Selection of the external component RS is discussed below, and other external

components are discussed in section 3. The subsequent sections describe the two options for control voltage

input at the ADJI pin: a pulse width modulation (PWM) control signal or a DC control voltage.

The ADJI pin has an input impedance

†

of 500kΩ ±25%.

2.3.1.

Output Current and RS

The current sense threshold voltage and the value of the external current sense resistor (RS) between VIN and

ISENSE set the output current through the LEDs (IOUT). Equation (1) shows this basic relationship. Unless the ADJ

pin is driven from an external voltage (see section 2.3.3), the minimum value for RS is 0.13

Ω to prevent exceeding

the maximum switch current (see section 1.3).

(1)

Where

IOUT = Nominal average output current through the LED(s)

RS

≥0.13Ω

† At room temperature.