Fairchild AN-7501 Data Handbook

Switching Waveforms Of The L2FET: A 5 Volt

Gate-Drive Power MOSFET

Application Note October 1999 AN-7501

The switching waveforms of a series of power MOSFET devices called Logic Level FETs (L2FETs) and featuring a VG = 9(4.5)V

RFM10N15

5V gate drive are presented and contrasted with those of the VG = 6(3)V

RFM10N15L

/Title more conventional 10V gate drive devices. A new method of

AN75 characterizing MOSFET switching performance is discussed VG = 5(2.5)V in which the MOSFET is treated as a vertical JFET driven in

1) cascade from a low voltage lateral MOS. The 2:1 advantage Sub- in rise and fall time and the 4:1 reduction in switching

ect “dynamic V(SAT)” dissipation with constant drive power of the VG = 4(2)V

L2FET over the 10V MOSFET are demonstrated and dis-

Switc cussed. ing ave- Background

orms DRAIN VOLTAGE (VD) (V)

A series of power MOSFET devices called Logic Level FETs,

f The FIGURE 1. DRAIN CURRENT vs. DRAIN VOLTAGE CURVES

or L2FETs, is compatible with the 5V power supply used for

FOR REPRESENTATIVE STANDARD AND L2FET

2FET logic circuitry. L2FETs retain the on resistance, drain current,

DEVICES

A 5 and blocking voltage ratings of their 10V predecessors, but

olt operate from a much less costly 5V supply.

VG = 9(4.5)V RFM10N15 ate- The reduction in gate drive voltage is the result of halving the RFM10N15L

VG = 7(3.5)V

rive thickness of the gate insulator from the industry standard VG = 6(3)V

IN (A

IN (A

100nm to 50nm (500Å). Since the surface inversion of the VG = 5(2.5)V

ower MOS channel is determined by the gate insulator voltage OS- field, halving the insulator thickness halves the required gate ET) voltage to achieve the same surface inversion thereby not compromising drain characteristics. Autho VG = 4(2)V

The apparent conclusion from a study of the switching wave- forms of the new device that halving the gate oxide thickness

Key- would double the gate capacitance and halve the switching ords

speed does not prove true. Measurements demonstrate

Inter- DRAIN VOLTAGE (VD) (V)

empirically a 2:1 increase in switching speed for the L2FET il over its 100nm predecessor, where gate drive power is the

same for both devices. The “dynamic V(SAT)” dissipation is FIGURE 2. DRAIN CURRENT vs. LOW DRAIN VOLTAGE

orpo-

CURVES FOR REPRESENTATIVE STANDARD

lowered by a factor of four. The apparent anomalies are

ation) AND L2FET DEVICES DEMONSTRATING THAT

explained with the aid of a new method of switching charac-

RON HAS NOT BEEN SACRIFICED IN THE L2FET

Cre- terization developed by treating the power MOSFET as a

grounded gate, depletion mode, vertical JFET driven in cas- Figures 1 and 2 are plots of drain current versus drain volt-

tor ()

cade by a grounded source, enhancement mode, lateral age with gate voltage as the running parameter. The L2FET

MOS. The waveforms and switching characterization meth- gate voltage is in parenthesis. The low drain voltage curves

FO ods are described in detail below. of Figure 2 demonstrate that r DS(ON) has not been sacrificed

df- in the L2FET. Figure 3 is the transfer characteristic compari-

L2FET Characteristics Compared to Standard Types -

son for three different temperatures. The abscissa has two

ark A Brief Review

scales to reflect the different gate sensitivities; again, the logic level part values are in parenthesis. It is evident from

A large number of power MOSFETs of the L2FET structure

the curve that:

have been announced. These devices were designed to be Page- totally interchangeable with the standard power MOSFET

1. The threshold voltage is scaled down by a factor of two for

with respect to output characteristics, while offering twice the

ode the L2FET.

gate sensitivity, as shown in Figures 1, 2, and 3, which are

comparisons of the industry standard RFM10N15 with its 2. The threshold voltage temperature coefficient in m V/o C is ut- Logic Level FET counterpart, the RFM10N15L. (Although scaled down.

ines the L suffix notation in the type number will ultimately be

3. The current level for zero temperature coefficient is un-

valid for the entire product matrix, the L2FET product cur-

changed.

rently available is available in both p-channel and n-channel

devices handling 200V or less, with 50A ratings or less.) 4. The transconductance is scaled up by a factor of two.

©2002 Fairchild Semiconductor Corporation Application Note 7501 Rev. A1