TC429
FIGURE 3-3:
SWITCHING TIME
DEGRADATION DUE TO
NEGATIVE FEEDBACK
+18V
FIGURE 3-4:
+18V
PEAK OUTPUT CURRENT
TEST CIRCUIT
TC429
2.4V
0V
0.1µF
2
4
1µF
1µF
18V
1
8 6,7
5
TEK Current
Probe 6302
0V
0.1µF
2500pF
2.4V
0V
0.1µF
2
4
1
8 6,7
5
TEK Current
Probe 6302
18V
0V
0.1µF
2500pF
Logic
Ground
300 mV
Power
Ground
6A
PC Trace Resistance = 0.05W
TC429
3.4
Power Dissipation
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 500µA 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 10µA 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.
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.
DS21416B-page 6
2002 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
