TC1426 datasheet(6/14 Pages) MICROCHIP

6 / 14 page

TC1426/TC1427/TC1428

DS21393B-page 6

 2002 Microchip Technology Inc.

3.0

APPLICATIONS INFORMATION

3.1

SUPPLY BYPASSING

Large currents are required to charge and discharge

capacitive loads quickly. For example, charging a

1000pF load to 16V in 25nsec requires a 0.8A current

from the device’s power supply.

To guarantee low supply impedance over a wide

frequency range, a parallel capacitor combination is

recommended for supply bypassing. Low-inductance

ceramic MLC capacitors with short lead lengths

(<0.5-in.) should be used. A 1.0

µF film capacitor in

parallel with one or two 0.1

µF ceramic MLC capacitors

normally provides adequate bypassing.

3.2

GROUNDING

The TC1426 and TC1428 contain inverting drivers.

Individual ground returns for the input and output

circuits or a ground plane should be used. This will

reduce negative feedback that causes degradation in

switching speed characteristics.

FIGURE 3-1:

INVERTING DRIVER

SWITCHING TIME

3.3

INPUT STAGE

The input voltage level changes the no-load or

quiescent 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 9mA. Logic "0" input level signals

reduce quiescent current to 500

µA maximum. Unused

driver inputs must be connected to VDD or GND.

Minimum power dissipation occurs for logic "0" inputs

for the TC1426/TC1427/TC1428.

The drivers are designed with 100mV of hysteresis.

This provides clean transitions and minimizes output

stage current spiking when changing states. Input

voltage thresholds are approximately 1.5V, making a

logic "1" input any voltage greater than 1.5V up to VDD.

Input current is less than 1

µA over this range.

The TC1426/TC1427/TC1428 may be directly driven

by the TL494, SG1526/27, TC38C42, TC170 and

similar switch-mode power supply integrated circuits.

FIGURE 3-2:

NONINVERTING DRIVER

SWITCHING TIME

+5V

10%

90%

10%

90%

10%

90%

VDD

µF

MKS-2

TC1426

(1/2 TC1428)

Test Circuit

0.1

µF MLC

Input

VDD = 16V

Output

CL = 1000pF

tD1

tD2

Input

Output

VDD

0.1

µF MLC

Input

VDD = 16V

Output

CL = 1000pF

tD1

tD2

Input

Output

90%

10%

90%

µF

WIMA

MKS-2

TC1427

(1/2 TC1428)

+5V

90%

Test Circuit

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