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MLD1N06CL

SMARTDISCRETES Internally Clamped, Current Limited N–Channel Logic Level Power MOSFET

Motorola => Freescale 

THE SMARTDISCRETES CONCEPT

From a standard power MOSFET process, several active

and passive elements can be obtained that provide on–chip

protection to the basic power device. Such elements require

only a small increase in silicon area and/or the addition of one

masking layer to the process. The resulting device exhibits

significant improvements in ruggedness and reliability as well

as system cost reduction. The SMARTDISCRETES device

functions can now provide an economical alternative to smart

power ICs for power applications requiring low on–resistance,

high voltage and high current.

These devices are designed for applications that require a

rugged power switching device with short circuit protection

that can be directly interfaced to a microcontroller unit (MCU).

Ideal applications include automotive fuel injector driver,

incandescent lamp driver or other applications where a high

in–rush current or a shorted load condition could occur.

OPERATION IN THE CURRENT LIMIT MODE

The amount of time that an unprotected device can with-

stand the current stress resulting from a shorted load before

its maximum junction temperature is exceeded is dependent

upon a number of factors that include the amount

of heatsinking that is provided, the size or rating of the device,

its initial junction temperature, and the supply voltage. Without

some form of current limiting, a shorted load can raise a de-

vice’s junction temperature beyond the maximum rated oper-

ating temperature in only a few milliseconds.

Even with no heatsink, the MLD1N06CL can withstand a

shorted load powered by an automotive battery (10 to 14

Volts) for almost a second if its initial operating temperature is

under 100°C. For longer periods of operation in the current–

limited mode, device heatsinking can extend operation from

several seconds to indefinitely depending on the amount of

heatsinking provided.

SHORT CIRCUIT PROTECTION AND THE EFFECT OF

TEMPERATURE

The on–chip circuitry of the MLD1N06CL offers an integrated

means of protecting the MOSFET component from high in–rush

current or a shorted load. As shown in the schematic diagram,

the current limiting feature is provided by an NPN transistor and

integral resistors R1 and R2. R2 senses the current through the

MOSFET and forward biases the NPN transistor’s base as the

current increases. As the NPN turns on, it begins to pull gate

drive current through R1, dropping the gate drive voltage across

it, and thus lowering the voltage across the gate–to–source of

the power MOSFET and limiting the current. The current limit is

temperature dependent as shown in Figure 3, and decreases

from about 2.3 Amps at 25°C to about 1.3 Amps at 150°C.

Since the MLD1N06CL continues to conduct current and dis-

sipate power during a shorted load condition, it is important to

provide sufficient heatsinking to limit the device junction tempera-

ture to a maximum of 150°C.

The metal current sense resistor R2 adds about 0.4 ohms to

the power MOSFET’s on–resistance, but the effect of tempera-

ture on the combination is less than on a standard MOSFET due

to the lower temperature coefficient of R2. The on–resistance

variation with temperature for gate voltages of 4 and 5 Volts is

shown in Figure 5.

Back–to–back polysilicon diodes between gate and source

provide ESD protection to greater than 2 kV, HBM. This on–chip

protection feature eliminates the need for an external Zener

diode for systems with potentially heavy line transients.

Motorola TMOS Power MOSFET Transistor Device Data

MLD1N06CL

4

VGS = 5 V

VDS = 7.5 V

3

2

1

0

–50

0

50

100

150

TJ, JUNCTION TEMPERATURE (°C)

Figure 3. ID(lim) Variation

With Temperature

4

ID = 1 A

3

2

25°C

TJ = –50°C 150°C

1

0

0

2

4

6

8

10

VGS, GATE–TO–SOURCE VOLTAGE (VOLTS)

Figure 4. RDS(on) Variation With

Gate–To–Source Voltage

1.25

ID = 1 A

1

VGS = 4 V

0.75

VGS = 5 V

0.5

0.25

–50

0

50

100

150

TJ, JUNCTION TEMPERATURE (°C)

Figure 5. On–Resistance Variation With

Temperature

3

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