July 14 2017 Preliminary A.01

TFR RAILWAY SERIES 24-Pin DIP

Up to 10 Watt DC-DC Converter

Input Capacitance at the Power Module

In order to avoid problems with loop stability, the converter must be

connected to a low impedance AC source and a low inductance source.

pins to de-couple distribution inductance. The external input capacitors

should have low ESR in order to quiet any ripple. Circuit as shown in the

figure below represents typical measurement methods for reflected

ripple current. The capacitor C1 and inductor L1 simulate the typical DC

source impedance. The input reflected-ripple current is measured by a

current probe oscilloscope with a simulated source Inductance (L1).

L1: 1µH

C1: None

Cin: 22µF ESR<0.7ohm @100KHz

Input Reflected-Ripple Test Setup

Test Set-Up

The basic test set-up to measure efficiency, load regulation, line

regulation and other parameters is shown in the next figure. When

testing the converter under any transient conditions, the user should

ensure that the transient response of the source is sufficient to power

the equipment under test. Below is the calculation of:

1-

Efficiency

2-

Load regulation

3-

Line regulation

The value of efficiency is defined as:

%

100

×

×

×

=

IN

IN

O

O

I

V

I

V

η

Where

The value of load regulation is defined as:

%

100

.

×

−

=

NL

NL

FL

V

V

V

reg

Load

Where

The value of line regulation is defined as:

%

100

.

×

−

=

LL

LL

HL

V

V

V

reg

Line

Where

TFR Series Test Setup

Output Ripple and Noise Measurement

The test set-up for noise and ripple measurements is shown in the figure

below. A coaxial cable was used to prevent impedance mismatch

reflections disturbing the noise readings at higher frequencies.

Measurements are taken with output appropriately loaded and all

+Vin

-Vin

-Vo

+Vo

R-Load

C2

Vin

+

-

BNC

To Scope

C1

Note:

C1: None

C2: 0.1uF Ceramic capacitor

Output Voltage Ripple and Noise Measurement Set-Up for Single

Output Model

C1: None

C2: 0.1uF Ceramic capacitor

Output Voltage Ripple and Noise Measurement Set-Up for Dual

Output Model

The conventional ground clip on an oscilloscope probe should never be

used in this kind of measurement. This clip, when placed in a field of

radiated high frequency energy, acts as an antenna or inductive pickup

loop, creating an extraneous voltage that is not part of the output noise

of the converter.

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