MIC4452YN datasheet(8/14 Pages) MICREL

8 / 14 page

Micrel Inc.

MIC4451/4452

January 2011

M9999-011811

Applications Information

To guarantee low supply impedance over a wide

frequency range, a parallel capacitor combination is

recommended for supply bypassing. Low inductance

ceramic disk capacitors with short lead lengths (< 0.5

inch) should be used. A 1µF low ESR film capacitor in

parallel with two 0.1µF low ESR ceramic capacitors,

(such as AVX RAM GUARD

®), provides adequate

bypassing. Connect one ceramic capacitor directly

between pins 1 and 4. Connect the second ceramic

capacitor directly between pins 8 and 5.

Supply Bypassing

Charging and discharging large capacitive loads quickly

requires large currents. For example, changing a

10,000pF load to 18V in 50ns requires 3.6A.

The MIC4451/4452 has double bonding on the supply

pins, the ground pins and output pins. This reduces

parasitic lead inductance. Low inductance enables large

currents to be switched rapidly. It also reduces internal

ringing that can cause voltage breakdown when the

driver is operated at or near the maximum rated voltage.

Grounding

The high current capability of the MIC4451/4452

demands careful PC board layout for best performance.

Since the MIC4451 is an inverting driver, any ground

lead impedance will appear as negative feedback which

can degrade switching speed. Feedback is especially

noticeable with slow-rise time inputs. The MIC4451 input

structure includes 200mV of hysteresis to ensure clean

transitions and freedom from oscillation, but attention to

layout is still recommended.

Internal ringing can also cause output oscillation due to

feedback. This feedback is added to the input signal

since it is referenced to the same ground.

DRI VE

LOGIC

φ1 DRIVE SIGNAL

CONDUCTION ANGLE

CONTROL 0° TO 180°

CONDUCTION ANGLE

CONTROL 180° TO 360°

MIC4451

VDD

1µF

VDD

MIC4452

VDD

1µF

VDD

φ1

φ3

φ2

PHASE 1 OF 3 PHASE MOTOR

DRI VER USIN G MI C4451/4452

Figure 5 shows the feedback effect in detail. As the

MIC4451 input begins to go positive, the output goes

negative and several amperes of current flow in the

ground lead. As little as 0.05Ω of PC trace resistance

can produce hundreds of millivolts at the MIC4451

ground pins. If the driving logic is referenced to power

ground, the effective logic input level is reduced and

oscillation may result.

To insure optimum performance, separate ground traces

should be provided for the logic and power connections.

Connecting the logic ground directly to the MIC4451

GND pins will ensure full logic drive to the input and

ensure fast output switching. Both of the MIC4451 GND

pins should, however, still be connected to power

ground.

Figure 3. Direct Motor Drive

MIC4451

1µF

50V

MKS2

UNITED CHEMCON SXE

0.1µF

WIMA

MKS2

6, 7

0.1µF

50V

5.6 kΩ

560 Ω

+15

560µF 50V

BYV 10 (x 2)

100µF 50V

(x2) 1N4448

Figure 4. Self Contained Voltage Doubler

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