MIC5016/5017

Micrel

MIC5016/5017

6

October 1998

driven to near supply immediately when the MIC5016/17 is

turned on. Typical circuits reach full enhancement in 50

µs or

less with a 15V supply.

Bootstrapped High Side Driver (Figure 3) The turn-on time

of a high side driver can be improved to faster than 40

µs by

bootstrapping the supply with the MOSFET source. The

Schottky barrier diode prevents the supply pin from dropping

more than 200mV below the drain supply, and improves turn-

on time. Since the supply current in the “OFF” state is only a

small leakage, the 100nF bypass capacitor tends to remain

charged for several seconds after the MIC5016/17 is turned

off. Faster switching speeds can be obtained at the expense

of supply voltage (the overvoltage shutdown will turn the part

off when the bootstrapping action pulls the supply pin above

35V) by using a larger capacitor at the junction of the two

1N4001 diodes. In a PWM application (this circuit can be

used for either PWM’ed or continuously energized loads), the

chip supply is sustained at a higher potential than the system

supply, which improves switching time.

Figure 3. Bootstrapped High-Side Driver

High Side Driver With Current Sense (Figure 4) Although no

current sense function is included on the MIC5016/17 de-

vices, a simple current sense function can be realized via the

addition of one more active component; an LM301A op amp

used as a comparator. The positive rail of the op amp is tied

chosen as it can withstand having input transients that swing

below the negative rail, and has common mode range almost

to the positive rail.

The inverting side of this comparator is tied to a voltage divider

is tied to the node between the drain of the FET and the sense

resistor. If the overcurrent trip point is not exceeded , this node

tor will be high which feeds the control input of the MIC5016

(polarities should be reversed if the MIC5017 is used). Once

the overcurrent trip point has been reached, the comparator

1/2 MIC5016

Control Input

OFF

ON

+2.75V to +30V

Gate

Gnd

Source

Input

V+

1µF

100nF

1N4001 (2)

1N5817

IRF540

will go low, which shuts off the MIC5016. When the short is

removed, feedback to the input pin insures that the MIC5016

will turn back on. This output can also be level shifted and sent

to an I/O port of a microcontroller for intelligent control.

Current Shunts (R

use at R

to 50m

Ω, at 2 to10W. If a precise overcurrent trip point is not

necessary, then a nonprecision resistor or even a measured

PCB trace can serve as R

values with such resistors is temperature coefficient; the

designer should be aware that a linear, 500ppm/

°C change

will contribute as much as 10% shift in the overcurrent trip

point.

If this is not acceptable, a power resistor designed for current

shunt service (drifts less than 100ppm/

°C), or a Kelvin-sensed

1/2 MIC5016

Gate

Gnd

Source

Input

V+

10µF

R4

1k

Ω

R

S

0.06

Ω

12V

On

R1

1k

Ω

R2

120k

Ω

LM301A

2.2k

Ω

= 1.7A

Figure 4. High Side Driver with Overcurrent Shutdown

† Suppliers of Precision Power Resistors:

Dale Electronics, Inc., 2064 12th Ave., Columbus, NE 68601. (402) 565-3131

International Resistive Co., P.O. Box 1860, Boone,NC 28607-1860.

(704) 264-8861

Isotek Corp., 566 Wilbur Ave. Swansea, MA 02777. (508) 673-2900

Kelvin, 14724 Ventura Blvd., Ste. 1003, Sherman Oaks, CA 91403-3501.

(818) 990-1192

RCD Components, Inc., 520 E. Industrial Pk. Dr., Manchester, NH 03103.

(603) 669-0054

Ultronix, Inc., P.O. Box 1090, Grand Junction, CO 81502 (303) 242-0810

High Side Driver With Delayed Current Sense (Figure 5)

Delay of the overcurrent detection to accomodate high inrush

loads such as incandescent or halogen lamps can be accom-

plished by adding an LM3905 timer as a one shot to provide

an open collector pulldown for the comparator output such

that the control input of the MIC5017 stays low for a preset

amount of time without interference from the current sense

circuitry. Note that an MIC5017 must be used in this applica-

tion (figure 5), as an inverting control input is necessary. The

delay time is set by the RC time constant of the external

components on pins 3 and 4 of the timer; in this case, 6ms was

chosen.

An LM3905 timer was used instead of a 555 as it provides a

clean transition, and is almost impossible to make oscillate.

Good bypassing and noise immunity is essential in this circuit

to prevent spurious op amp oscillations.