MIC5014/5015

Micrel

1997

5-141

5

MIC5014

Control Input

OFF

ON

1

2

3

4

8

7

6

5

+3V to +30V

NC

Gate

Gnd

Source

Input

V+

NC

NC

10µF

Figure 2. Low Side Driver

not use a socket for the MOSFET. If the MOSFET is a TO-220

type package, make high current connections to the drain tab.

Wiring losses have a profound effect on high-current circuits.

A floating milliohmeter can identify connections that are con-

tributing excess drop under load.

Low Voltage Testing

As the MIC5014/MIC5015 have relatively high output imped-

ances, a normal oscilloscope probe will load the device. This

is especially pronounced at low voltage operation. It is recom-

mended that a FET probe or unity gain buffer be used for all

testing.

Circuit Topologies

The MIC5014 and MIC5015 are well suited for use with

standard power MOSFETs in both low and high side driver

configurations. In addition, the lowered supply voltage re-

quirements of these devices make them ideal for use with logic

level FETs in high side applications with a supply voltage of 3

to 4V. (If higher supply voltages [>4V] are used with logic level

FETs, an external zener clamp must be supplied to ensure

exceeded.) In addition, a standard IGBT can be driven using

these devices.

Choice of one topology over another is usually based on

speed vs. safety. The fastest topology is the low side driver,

however, it is not usually considered as safe as high side

driving as it is easier to accidentally short a load to ground than

The slowest, but safest topology is the high side

driver; with speed being inversely proportional to supply

voltage. It is the preferred topology for most military and

automotive applications. Speed can be improved consider-

ably by bootstrapping from the supply.

All topologies implemented using these devices are well

suited to driving inductive loads, as either the gate or the

source pin can be pulled 20V below ground with no effect.

External clamp diodes are unnecessary, except for the case

in which a transient may exceed the overvoltage trip point.

High Side Driver (Figure 1) The high side topology shown

here is an implementation of a “sleep-mode” switch for a

laptop or notebook computer which uses a logic level FET. A

standard power FET can easily be substituted when supply

voltages above 4V are required.

Applications Information

Functional Description

The MIC5014 is functionally and pin for pin compatible with

the MIC5011, except for the omission of the optional speed-

up capacitor pins, which are available on the MIC5011. The

MIC5015 is an inverting configuration of the MIC5014.

The internal functions of these devices are controlled via a

logic block (refer to block diagram) connected to the control

input (pin 2). When the input is off (low for the MIC5014, and

high for the MIC5015), all functions are turned off, and the

gate of the external power MOSFET is held low via two N-

channel switches. This results in a very low standby current;

15

µAtypical,whichisnecessarytopoweraninternalbandgap.

When the input is driven to the “ON” state, the N-channel

switches are turned off, the charge pump is turned on, and the

P-channel switch between the charge pump and the gate

turns on, allowing the gate of the power FET to be charged.

The op amp and internal zener form an active regulator which

shuts off the charge pump when the gate voltage is high

enough. This is a feature not found on the MIC5011.

The charge pump incorporates a 100kHz oscillator and on-

chip pump capacitors capable of charging a 1,000pF load in

90

µs typical. In addition to providing active regulation, the

rating of the power MOSFET at high supply voltages.

The MIC5014/15 devices have been improved for greater

ruggedness and durability.

All pins can withstand being

pulled 20V below ground without sustaining damage, and the

supply pin can withstand an overvoltage transient of 60V for

1s. An overvoltage shutdown has also been included, which

turns off the device when the supply exceeds 35V.

Construction Hints

High current pulse circuits demand equipment and assembly

techniques that are more stringent than normal, low current

lab practices. The following are the sources of pitfalls most

often encountered during prototyping:

Supplies : Many bench

power supplies have poor transient response. Circuits that

are being pulse tested, or those that operate by pulse-width

modulation will produce strange results when used with a

supply that has poor ripple rejection, or a peaked transient

response. Always monitor the power supply voltage that

appears at the drain of a high side driver (or the supply side

of the load for a low side driver) with an oscilloscope. It is not

uncommon to find bench power supplies in the 1kW class that

overshoot or undershoot by as much as 50% when pulse

loaded. Not only will the load current and voltage measure-

ments be affected, but it is possible to overstress various

components, especially electrolytic capacitors, with possibly

catastrophic results. A 10

µF supply bypass capacitor at the

chip is recommended. Residual resistances: Resistances

in circuit connections may also cause confusing results. For

example, a circuit may employ a 50m

Ω power MOSFET for

low voltage drop, but unless careful construction techniques

are used, one could easily add 50 to 100m

Ω resistance. Do