MC33167 Просмотр технического описания (PDF) - ON Semiconductor

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MC33167

5.0 A, Step-Up/Down/Inverting Switching Regulators

ON Semiconductor 

MC34167, MC33167

Switch Output

The output transistor is designed to switch a maximum of

40 V, with a minimum peak collector current of 5.5 A. When

configured for step–down or voltage–inverting applications,

as in Figures 19 and 23, the inductor will forward bias the

output rectifier when the switch turns off. Rectifiers with a

high forward voltage drop or long turn on delay time should

not be used. If the emitter is allowed to go sufficiently

negative, collector current will flow, causing additional

device heating and reduced conversion efficiency. Figure 9

shows that by clamping the emitter to 0.5 V, the collector

current will be in the range of 100 µA over temperature. A

1N5825 or equivalent Schottky barrier rectifier is

recommended to fulfill these requirements.

Undervoltage Lockout

An Undervoltage Lockout comparator has been

incorporated to guarantee that the integrated circuit is fully

functional before the output stage is enabled. The internal

reference voltage is monitored by the comparator which

enables the output stage when VCC exceeds 5.9 V. To prevent

erratic output switching as the threshold is crossed, 0.9 V of

hysteresis is provided.

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.

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