EB201/D

http://onsemi.com

5

ringing in the parasitic components. Therefore, when

of recovery abruptness and thus gives a comparative

estimate of probable noise. So, although the diode recovery

time is only a fraction of the total commutation time, the

noise

generated

by

the

diode’s

abruptness

limits

commutation speeds and determines system switching

losses.

Compared to the diodes of standard cell density

MOSFETs,

ON

Semiconductor’s

high

cell

density

charge, and have a softer reverse recovery (Figure 5).

Figure 6 shows that some high cell density devices are just

as noisy as their predecessors. The softness advantage of

HDTMOS diodes means they can be forced through reverse

recovery at a higher di/dt than that of a standard cell

MOSFET diode without increasing the current ringing or

generating more noise. Generalizing about how much faster

time is in part a function of circuit layout. However, a

maximum reduction of about 50% seems feasible.

One precaution required when using the body diode of a

approximately 1 V at elevated current, which is typical of a

likely to be high. So if the diode’s duty cycle is high, the

on–state losses of the diode must be considered. The diode’s

high forward voltage can be decreased by turning on the

MOSFET when its diode is to conduct. With the gate on,

current flows through the channel (source–to–drain), and

the voltage drop is equal to that of the MOSFET in its

conventional direction.

Switching Speed and Ruggedness

Except for on–resistance and body diode performance,

high cell density devices are very similar to existing

MOSFET

technology.

For

example,

the

output

characteristics and gate charge curves of high cell density

devices have the same general characteristics as those of

standard devices. For a given die size, HDTMOS devices

require more gate charge than their standard counterparts.

However, for a given on–resistance, HDTMOS devices

have lower gate charge and they switch faster. Standard and

high cell density gate charge waveforms, those of

the

MTP50N05E (28 m

Ω, 163 mils by 200 mils) and the

MTP75N05HD (9.5 m

Ω, 170 mils by 220 mils), are shown

in Figure 7.

Figures 8 and 9 show the switching behavior of the

MTP50N05E and the MTP75N05HD. The HDTMOS

device is slower due to its higher per unit area input

capacitance and larger die area. Had the comparison been

based on the same on–resistance, it would have favored the

HDTMOS device.

Figure 6. Diode Reverse Recovery Compared to

Competition

0

RFG70N06

MTP75N05HD

di/dt = 100 A/microsecond, lfm = 25 A

20 ns/DIV

Figure 7. Gate Charge Comparison Between

Standard TMOS and HDTMOS

MTP50N05E

MTP75N05HD

0

Gate Charge (10 nC/DIV)

Today’s reliability requirements mandate that all new

high current MOSFETs be rugged with respect to

overvoltage transients that might appear across the

drain–source of the MOSFET. They must be able to handle

avalanche currents of at least their continuous current rating.

HDTMOS devices are no exception to this rule. The

ruggedness of both standard and HDTMOS are limited by

maximum junction temperature, so for a given die area, they

have roughly the same unclamped inductive switching

capability.