CYStech Electronics Corp.

Spec. No. : C547F3

Issued Date : 2007.09.26

Revised Date

Page No. : 3/6

PL1084A-XXXF3

CYStek Product Specification

Note: 1. See thermal regulation specifications for changes in output voltage due to heating effects. Line and load regulation are

measured at a constant junction temperature by low duty cycle pulse testing. Load regulation is measured at the output

lead =1/18” from the package.

2. Line and load regulation are guaranteed up to the maximum power dissipation of 15W. Power dissipation is determined

by the difference between input and output and the output current. Guaranteed maximum power dissipation will not be

over the full input/output range.

Block Diagram

Functional Description

Introduction

The PL1084A adjustable Low Dropout(LDO) regulator is a 3 terminal device that can easily be programmed with the

addition of two external resistors to any voltages within the range of 1.25V to 2.5V. The PL1084A only needs 1.5V

differential between Vin and Vout to maintain output regulation. In addition, the output voltage tolerances are also

extremely tight and they include the transient response as part of the specification. For example, Intel VRE

specification calls for a total of ±100mV including initial tolerance, load regulation and 0 to 5A load step. The

PL1084A is specifically designed to meet the fast current transient needs as well as providing an accurate initial

voltage, reducing the overall system cost with the need for fewer output capacitors.

Output Voltage Setting

The PL1084A can be programmed to any voltages in the range of 1.25V to 5V with the addition of R1 and R2

external resistors according to the following formula:

Vout=Vref(1+R2/R1)+Iadj*R2, where Vref=1.25V typically, Iadj=55μA typically

The PL1084A keeps a constant 1.25V between the output pin and the adjust pin. By placing a resistor R1 across these

two pins, a constant current flows through R1, adding to the Iadj current requirement of the PL1084A. R1 is typically

selected to be 121Ω resistor so that it automatically satisfies the minimum current requirement. Notice that since

Iadj is typically in the range of 55μA, it only adds a small error to the output voltage and should only be considered

when a very precise output voltage setting is required. For example, in a typical 3.3V application where R1=121Ω

and R2=200Ω, the error due to Iadj is only 0.3% of the nominal set point.