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GM7130HV

3A STEP DOWN VOLTAGE SWITCHING

REGULATORS

Application Hints

The regulator input pin must be by-passed with at least a 100

μF electrolytic capacitor to maintain

stability. The capacitor

’s leads must be kept short, and located near GM1730HV. If the operating

temperature range includes temperature below -25°C, the input capacitor value may need to be larger.

With most electrolytic capacitors, the capacitance value decreases and the ESR increase with lower

temperature and age. It is suggested to parallel a ceramic or solid tantalum capacitor to increase the

stability at cold temperature.

It is n should be used for best results. When using the Adjustable

version, place the programming resistors as close as possible to GM7130HV, to keep the sensitive

feedback wiring short.

Inductor Selection

All switching regulators have two basic modes of operation: continuous and discontinuous. The

difference between the two types relates to the inductor current, whether it is flowing continuously, or if

it drops to zero for a period of time in the normal switching cycle. Each mode has distinctively different

operating characteristics, which can affect the regulator performance and requirements. The

GM7130HV can be used for both continuous and discontinuous modes of operation.

Inductors are available in different styles such as pot core, toriod, E-frame, bobbin core, etc., as well

as different core materials, such as ferrites and powdered iron. The least expensive, the bobbin core

type, consists of wire wrapped on a ferrite rod core. This type of construction makes for an inexpensive

inductor, but since the magnetic flux is not completely contained within the core, it generates more

electromagnetic interference (EMI). This EMI can cause problems in sensitive circuits, or can give

incorrect scope readings because of induced voltages in the scope probe.

An inductor should not be operated beyond its maximum rated current because it may saturate. When

an inductor begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly

a resistor (the DC resistance of the winding). This will cause the switch current to rise very rapidly.

Different inductor types have different saturation characteristics, and this should be kept in mind when

selecting an inductor.

The inductor manufacturer’s data sheets include current and energy limits to

avoid inductor saturation.