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TELCOM SEMICONDUCTOR, INC.

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TC426

TC427

TC428

1.5A DUAL HIGH-SPEED

POWER MOSFET DRIVERS

*Static-sensitive device. Unused devices must be stored in conductive

material. Protect devices from static discharge and static fields. Stresses

above those listed under "Absolute Maximum Ratings" may cause perma-

nent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions above those

indicated in the operational sections of the specifications is not implied.

Exposure to absolute maximum rating conditions for extended periods may

effect device reliability.

SUPPLY BYPASSING

Charging and discharging large capacitive loads quickly

requires large currents. For example, charging a 1000-pF

load to18V in 25nsec requires an 0.72A current from the

device power supply.

To guarantee low supply impedance over a wide fre-

quency range, a parallel capacitor combination is recom-

mended for supply bypassing. Low-inductance ceramic

disk capacitors with short lead lengths (< 0.5 in.) should be

used. A 1

µF film capacitor in parallel with one or two

0.1

µF ceramic disk capacitors normally provides adequate

bypassing.

GROUNDING

The TC426 and TC428 contain inverting drivers. Ground

potential drops developed in common ground impedances

from input to output will appear as negative feedback and

degrade switching speed characteristics.

Individual ground returns for the input and output

circuits or a ground plane should be used.

INPUT STAGE

The input voltage level changes the no-load or quies-

cent supply current. The N-channel MOSFET input stage

transistor drives a 2.5mA current source load. With a logic

"1" input, the maximum quiescent supply current is 8 mA.

Logic "0" input level signals reduce quiescent current to

0.4 mA maximum. Minimum power dissipation occurs for

logic "0" inputs for the TC426/427/428. Unused driver

The drivers are designed with 100 mV of hysteresis.

This provides clean transitions and minimizes output stage

current spiking when changing states. Input voltage thresh-

olds are approximately 1.5V, making the device TTL com-

patible over the 4.5V to 18V supply operating range. Input

current is less than 1

µA over this range.

The TC426/427/428 may be directly driven by the

TL494, SG1526/1527, SG1524, SE5560, and similar switch-

mode power supply integrated circuits.

POWER DISSIPATION

The supply current vs frequency and supply current vs

capacitive load characteristic curves will aid in determining

power dissipation calculations.

The TC426/427/428 CMOS drivers have greatly re-

duced quiescent DC power consumption. Maximum quies-

cent current is 8 mA compared to the DS0026 40 mA

specification. For a 15V supply, power dissipation is typi-

cally 40 mW.

Two other power dissipation components are:

• Output stage AC and DC load power.

• Transition state power.

Output stage power is:

Where:

Vo = DC output voltage

f

= Switching frequency

Vs = Supply voltage

negligible. MOSFET power transistors are high imped-

ance, capacitive input devices. In applications where resis-

normally dominate.

cases:

A.

B.

1. f

= 20kHZ

1. f

= 200kHz

=1000pf

=1000pf

3. Vs

= 18V

3. VS

=15V

During output level state changes, a current surge will

flow through the series connected N and P channel output

MOSFETS as one device is turning "ON" while the other is

turning "OFF". The current spike flows only during output

transitions. The input levels should not be maintained be-

tween the logic "0" and logic "1" levels. Unused driver

inputs must be tied to ground and not be allowed to

float. Average power dissipation will be reduced by mini-

mizing input rise times. As shown in the characteristic

curves, average supply current is frequency dependent.