MC34167 MC33167

7

MOTOROLA ANALOG IC DEVICE DATA

Thermal Protection

Internal Thermal Shutdown circuitry is provided to protect

the integrated circuit in the event that the maximum junction

temperature is exceeded. When activated, typically at 170

°C,

the latch is forced into a ‘reset’ state, disabling the output

switch. This feature is provided to prevent catastrophic failures

from accidental device overheating. It is not intended to be

used as a substitute for proper heatsinking. The MC34167

is contained in a 5–lead TO–220 type package. The tab of the

package is common with the center pin (Pin 3) and is normally

connected to ground.

DESIGN CONSIDERATIONS

Do not attempt to construct a converter on wire–wrap

or plug–in prototype boards. Special care should be taken

to separate ground paths from signal currents and ground

paths from load currents. All high current loops should be

kept as short as possible using heavy copper runs to

minimize ringing and radiated EMI. For best operation, a tight

component layout is recommended. Capacitors Cin, CO, and

all feedback components should be placed as close to the IC

as physically possible. It is also imperative that the Schottky

diode connected to the Switch Output be located as close to

the IC as possible.

Figure 15. Low Power Standby Circuit

Figure 16. Over Voltage Shutdown Circuit

Figure 17. Soft–Start Circuit

1

5

R1

120

Error

Amp

Compensation

100

µA

I = Standby Mode

VShutdown = VZener + 0.7

tSoft–Start ≈ 35,000 Css

Css

D1

D2

1.0 M

Vin

1

5

R1

120

Error

Amp

Compensation

100

µA

1

5

R1

120

Error

Amp

Compensation

100

µA

+

+

+