ZLED7002 Datasheet

© 2016 Integrated Device Technology, Inc.

7

April 20, 2016













+

=

−

2

R

1

R

2

R

V

V

CC

PIN

UV













=

3

R

V

8000

I

ISET

MAIN

2.2.

Under-Voltage Threshold

The ZLED7002’s UV pin enables under-voltage detection. When a high-to-low transition occurs on the power supply voltage and

the voltage at the UV pin falls below the under-voltage threshold (typically 1.17V), the ZLED7002 automatically turns off the MAIN

LED channel and actives the SUB channel. There is an 80mV hysteresis for the under-voltage threshold to prevent unintended

activation due to power supply ripple. When a low-to-high transition occurs on the power supply voltage, the SUB channel is turned

off and the MAIN channel is activated if the UV pin voltage is 80mV (typical) above the under-voltage threshold.

(1)

If the values for R1 and R2 are low, high current will flow through them resulting in lower system efficiency. Typical values for R1

and R2 are in the magnitude of 10

Ω. For design purposes, it is helpful to select the value for R2 first and then compute

R1 as needed to achieve the target ratio.

recommended.

2.3.

Main LED Current

The R3 resistor connected between the Iset and GND pins determines the level of the constant current through the MAIN LED

channel, which is typically 8000 times the current of the Iset pin. The voltage at the Iset pin is a constant 1.2V, which is unaffected

by environmental temperature and any power supply voltage changes as shown in Figure 1.1 and Figure 1.2.

The MAIN LED current flows through the MAIN pin to ground, so voltage dropout is minimal (as low as 0.1V when the MAIN

channel current is 200mA).

Note: System efficiency is reduced if the power supply voltage is larger than the MAIN LED’s voltage. In this case, the additional

voltage is added to the MAIN pin voltage.

(2)

2.4.

Sub LED Current

The SUB LED channel current is determined by the external R4 resistor in series with the connected SUB LED string, the SUB

LED forward voltage, and the voltage drop across the D1 Zener diode connected from the cathode of the SUB LED to the SUB pin.

When the SUB channel is active, its current flows through the SUB pin to ground.