TC429

DS21416B-page 6

 2002 Microchip Technology Inc.

FIGURE 3-3:

SWITCHING TIME

DEGRADATION DUE TO

NEGATIVE FEEDBACK

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 3mA current source load.

With a logic “1” input, the maximum quiescent supply

current is 5mA. Logic “0” input level signals reduce

quiescent current to 500

µA maximum.

The TC429 input is designed to provide 300mV of

hysteresis, providing clean transitions and minimizing

output stage current spiking when changing states.

Input voltage levels are approximately 1.5V, making the

device TTL compatible over the 7V to 18V operating

supply range. Input current is less than 10

µA over this

range.

The TC429 can be directly driven by TL494, SG1526/

1527,

SG1524,

SE5560 or

similar

switch-mode

power supply integrated circuits. By off-loading the

power-driving duties to the TC429, the power supply

controller can operate at lower dissipation, improving

performance and reliability.

FIGURE 3-4:

PEAK OUTPUT CURRENT

TEST CIRCUIT

3.4

Power Dissipation

CMOS circuits usually permit the user to ignore power

dissipation. Logic families such as the 4000 and 74C

have outputs that can only supply a few milliamperes of

current, and even shorting outputs to ground will not

force enough current to destroy the device. The TC429,

however, can source or sink several amperes and drive

large capacitive loads at high frequency. The package

power dissipation limit can easily be exceeded.

Therefore, some attention should be given to power

dissipation when driving low impedance loads and/or

operating at high frequency.

The supply current versus frequency and supply

current versus capacitive load characteristic curves will

aid in determining power dissipation calculations.

Table 3-1 lists the maximum operating frequency for

several power supply voltages when driving a 2500pF

load. More accurate power dissipation figures can be

obtained by summing the three power sources.

Input signal duty cycle, power supply voltage and

capacitive load influence package power dissipation.

Given power dissipation and package thermal resis-

tance, the maximum ambient operation temperature

is easily calculated. The 8-pin CERDIP junction-to-

ambient thermal resistance is 150

°C/W. At +25°C, the

package is rated at 800mW maximum dissipation.

Maximum allowable chip temperature is +150

°C.

TC429

1

µF

0.1

µF

0.1

µF

0V

18V

2.4V

0V

Logic

Ground

Power

Ground

300 mV

6A

PC Trace Resistance = 0.05W

2500pF

1

8

6,7

5

4

2

+18V

TEK Current

Probe 6302

TC429

1

µF

0.1

µF

0.1

µF

0V

18V

2.4V

0V

2500pF

1

8

6,7

5

4

2

TEK Current

Probe 6302

+18V