ZXLD1350Q 查看數據表（PDF） - Diodes Incorporated.

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ZXLD1350Q

AUTOMOTIVE COMPLIANT 350mA BUCK LED DRIVER

Diodes Incorporated. 

ZXLD1350Q

Device Description

The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a self-oscillating continuous-mode buck converter.

Device Operation (Refer to block diagram and Figure 1 - Operating waveforms)

tOFF

tON

Figure 1. Theoretical Operating Waveforms

Operation can be best understood by assuming that the ADJ pin of the device is unconnected and the voltage on this pin (VADJ) appears directly at

the (+) input of the comparator.

When input voltage VIN is first applied, the initial current in L1 and RS is zero and there is no output from the current sense circuit. Under this

condition, the (-) input to the comparator is at ground and its output is high. This turns MN on and switches the LX pin low, causing current to flow

from VIN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by VIN and L1 to produce a voltage ramp (VSENSE) across RS.

The supply referred voltage VSENSE is forced across internal resistor R1 by the current sense circuit and produces a proportional current in internal

resistors R2 and R3. This produces a ground referred rising voltage at the (-) input of the comparator. When this reaches the threshold voltage

(VADJ), the comparator output switches low and MN turns off. The comparator output also drives another NMOS switch, which bypasses internal

resistor R3 to provide a controlled amount of hysteresis. The hysteresis is set by R3 to be nominally 15% of VADJ.

When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to VIN. The current decays at a rate determined by the LED and

diode forward voltages to produce a falling voltage at the input of the comparator. When this voltage returns to VADJ, the comparator output

switches high again. This cycle of events repeats, with the comparator input ramping between limits of VADJ ± 15%.

ZXLD1350Q

Document number: DS37076 Rev. 2 - 2

5 of 21

www.diodes.com

September 2017

© Diodes Incorporated

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