ZXLD383

ZXLD383

Document number: DS32189 Rev. 3 - 2

4 of 10

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May 2010

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Device Description

The ZXLD383 is a simple PFM, DC-DC controller combined with a high performance internal switching transistor, enabling

the production of a high efficiency boost converter for use in single cell applications. It includes a dual function Enable input

which serves both as an operation inhibit control and an ultra-low voltage drop isolation diode for battery charging purposes

in Garden Light applications. A block diagram is shown for the ZXLD383 in Figure 1.

which forces the supply voltage across the external inductor L1. This causes a current to build up, storing energy in the

inductor. During this phase, switch current and supply voltage are monitored and used by the pulse control circuit to

determine the optimum drive conditions and on-time. At the end of the energy charge cycle, the internal switch is turned off

starting the energy discharge cycle. With the voltage across the inductor reversed, the current flowing through it (and the

sensed by the pulse control circuit and is combined with the output of an off-period timer to initiate the next energy charge

cycle. Except for low level losses, all the energy stored in the inductor during a charge cycle is channeled to the load LED

during the following discharge cycle.

The current fed into the load LED has a sawtooth waveform, the average (DC) value of which is kept constant by the pulse

control circuit for varying supply voltage and temperature. It is possible to change the output current given by the ZXLD383

by changing the value of inductor L1. The larger the inductance of L1, the lower the output current. A table/graph showing

the relationship between inductance and output current is given later in this datasheet. Since the output current of the

ZXLD383 is a sawtooth waveform, its peak value is substantially larger than the DC/average value. The table also provides

this data.

The internal switching transistor has a minimum collector-emitter breakdown voltage of 20V and this sets the maximum

load voltage allowable. The minimum value is set by a feature of the pulse control circuit that requires the load voltage to

will be impaired.) Higher than nominal load voltages will lower the average (DC) output current generated for a given

inductor value.

The Enable pin inhibits the operation of the output switch if held at a potential of Vcc-0.8V or lower. It also includes a diode

to ground which allows the input to be wired directly to a photocell array that will then both enable operation of the

converter when in darkness and charge the IC’s power source in daylight conditions. The diode function is performed by an

active circuit that gives an ultra low forward voltage drop (typically less than 0.1V at 20mA). This allows the use of a lower

output voltage photocell array (lower cost) without degrading performance.