MC34063ABuck / boost / inverting controller

One switching controller. Three ways to change a DC rail.

Manufacturer-referenced

Texas Instruments · MC34063AP

PDIP-8SLLS636N · January 2015

MC34063A is an eight-pin switching controller with an internal NPN power switch, reference, comparator, oscillator and current-limit circuit. External connections configure it as a buck, boost or inverting converter. Its 1.5 A headline rating describes peak switch current. Available output current depends on topology, voltage ratio, inductor ripple and cooling; a boost output cannot simply deliver 1.5 A at every voltage. This reference follows TI’s commercial 0–70°C MC34063A in PDIP-8 and SOIC-8. The illustrated buck circuit follows the manufacturer’s example, with its resistor-selected output and distinct current-sense, timing and feedback nodes.

Real View

MC34063AP black package with silver leads and readable markings.

Pinout

MC34063APPDIP-8Top view

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8Physical pins MC34063APPDIP-8 Manufacturer-referencedTexas Instruments

Pin diagram

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Package map

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MC34063APPDIP-8Top view

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PIN 1 · Power switch

SC

Switch collector

Function

Collector of the internal high-current NPN switch.

How to connect

In the buck example, connect to the current-sense resistor output and driver collector pin 8.

Electrical note

The 1.5 A rating is a peak switch limit, not a guaranteed load current.

Key specifications

The external inductor and diode carry the energy. CT controls timing, RSC limits peak current and the output divider sets the regulated voltage.

Supply range3–40 V

Peak switch limit1.5 A · not load current

Ambient range0–70 °C · MC34063A

Nominal reference1.25 V

Operating profile

Supply, signals and operating conditions

MC34063A operating profile
Parameter	Value	Conditions / notes
Selected package	PDIP-8	MC34063AP
Oscillator example	33 kHz	Typical at CT = 1 nF
Set the output	R2 / R1	Feedback at pin 5

Package details

MC34063AP · PDIP-8

Selected package

Selected MC34063A physical package
Property	Details
Manufacturer	Texas Instruments
Part number	MC34063AP
Package	PDIP-8
Connections	8 pins
Mounting	Through-hole
Lead pitch	2.54 mm
Package code	dip
Thermal reference	Board and package dependent; see manufacturer data

Operating conditions

Selected commercial MC34063A

Manufacturer specifications 6 parameters

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Parameter	Value	Conditions / notes
Supply	3–40 V	Recommended VCC range
Ambient temperature	0 to +70°C	MC34063A; MC33063A is a separately specified −40 to +85°C option
Topologies	Buck / boost / inverting	External wiring and calculations differ
Maximum oscillator capability	100 kHz	External CT and the operating conditions determine actual timing
Peak switch current	1.5 A	Not a guaranteed continuous load current
Packages shown	PDIP-8 / SOIC-8	TI P / D orderables

Keep voltage overshoot and thermal stress within the exact device ratings.

Oscillator and current limit

VCC = 5 V; TA = 25°C unless noted

Manufacturer specifications 6 parameters

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Parameter	Value	Conditions / notes
Frequency with CT = 1 nF	24 / 33 / 42 kHz	Minimum / typical / maximum; pin 5 at 0 V
Capacitor charge current	24 / 35 / 42 µA	VCC = 5–40 V
Capacitor discharge current	140 / 220 / 260 µA	VCC = 5–40 V
Discharge / charge ratio	5.2 / 6.5 / 7.5	Pin 7 tied to VCC
Current-limit sense voltage	250 / 300 / 350 mV	Characterized at equal charge and discharge currents
Nominal sense resistor	RSC ≈ 0.3 / IPEAK	Use threshold tolerance and waveform margins

The CT = 1 nF frequency is a test point, not the frequency of the illustrated 470 pF circuit.

Reference, switch and supply

TI electrical-characteristic conditions

Manufacturer specifications 6 parameters

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Parameter	Value	Conditions / notes
Reference at 25°C	1.225 / 1.250 / 1.275 V	Minimum / typical / maximum
Reference over ambient range	1.21–1.29 V	Commercial operating range
Reference line change	1.4 mV typical; 5 mV maximum	VCC = 5–40 V
Darlington switch saturation	1 V typical; 1.3 V maximum	ISW = 1 A; pins 1 and 8 joined
Non-Darlington saturation	0.45 V typical; 0.7 V maximum	ISW = 1 A, 82 Ω driver feed, forced beta about 20
Supply current	4 mA maximum	VCC = 5–40 V; output-switch-off test conditions

Driver topology changes switching loss and turn-off behavior. Use the complete manufacturer conditions.

Buck example components

TI Figure 11 · 25 V input, approximately 5 V output

Manufacturer specifications 7 parameters

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Parameter	Value	Conditions / notes
RSC	0.33 Ω	Between VIN and the joined SC1 / IPK7 / DC8 feed
CT	470 pF	Pin 3 to ground
L1	220 µH	Pin 2 to filtered output; select suitable saturation and RMS ratings
Catch diode	1N5819	Cathode at pin 2; anode at GND
CIN / COUT	100 µF / 470 µF	Choose voltage/ripple ratings and suitable ESR; illustrated 50 V / 16 V
R2 / R1	3.8 kΩ / 1.2 kΩ	R2 from output to INV5; R1 from INV5 to GND
Reference load	500 mA	Manufacturer application example, not the part’s universal current rating

The optional extra LC output filter is omitted from the illustration. The nominal resistor ratio gives 5.208 V before tolerance and losses.

Read the example correctly

Calculated illustrations

Manufacturer specifications 6 parameters

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Parameter	Value	Conditions / notes
Divider output	5.208 V	1.25 × (1 + 3.8/1.2)
Nominal current limit	0.909 A	0.300 V / 0.33 Ω
Threshold-only limit interval	0.758–1.061 A	0.250–0.350 V / 0.33 Ω; excludes resistor tolerance and dynamic effects
Ideal duty at 25 V	20.8%	5.208 / 25; excludes switch/diode drops
Output power at 0.5 A	Approximately 2.60 W	5.208 V × 0.5 A
Simple resistor load	About 10.4 Ω	For an illustrative 0.5 A load; rate it above the dissipated power

These calculations explain the circuit. They are not live measurements or a switching simulation.

Layout and connection checks

Protect quiet nodes from switching currents

Manufacturer specifications 6 parameters

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Parameter	Value	Conditions / notes
Current-sense path	VIN6 → RSC → IPK7 / SC1 / DC8	Use short, low-inductance paths and sense the resistor terminals
Switch node	SE2 → L1 and diode cathode	Keep copper compact
Catch path	GND → diode → SE2 → L1	Short loop with the output capacitor
Feedback divider	Output → R2 → INV5 → R1 → GND	Route away from switch-node copper
Timing capacitor	CT3 → GND4	Place close to the IC
Physical package mapping	Eight pins in both selected packages	Pin 1 indication remains visible

Changing from buck to boost or inverting operation requires a different power-stage connection.

Stress and thermal limits

Absolute maxima are not normal targets

Manufacturer specifications 6 parameters

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Parameter	Value	Conditions / notes
Supply / switch voltage	40 V	Absolute limits require checking each referenced voltage
Driver collector current	100 mA	Absolute maximum
Switch current	1.5 A	Absolute maximum
Junction temperature	150°C	Absolute maximum; thermal design must stay below it
Storage temperature	−65 to +150°C	Unpowered
Comparator input	−0.3 to +40 V	Absolute input range, not a desired feedback voltage

A headline current rating cannot replace dissipation and temperature calculations.

Connections by function

Select a pin for its function, connection guidance and electrical notes.

Power switch2 pins

Oscillator1 pin

Ground1 pin

Feedback1 pin

Supply1 pin

Current sense1 pin

Switch driver1 pin

MC34063A working principle: illustrated functional stages, basic circuit and connections — Select the diagram to read it at full resolution.

How it works

3 stages · Explore one step at a time

Step 1 / 3

Start an energy pulse

The timing capacitor controls the oscillator. When feedback requests energy, the driver turns the output switch on.

Step 2 / 3

Limit the current

The drop across RSC increases with switch-path current. The sense circuit changes the timing when its threshold is reached.

Step 3 / 3

Hold the output near its setting

Pin 5 compares the divided output against 1.25 V. The inductor and catch diode continue supplying current between switching pulses.

MC34063A buck circuit with 0.33ohm sense resistor, 470pF timing capacitor, 220uH inductor,1N5819,100uF input,470uF output and 3.8k/1.2k divider. — Adapted from TI Figure 11. All equal supply labels and GND symbols share their named net. Check actual parts, layout, heat and startup.

Connect it, step by step

Follow the component values and pin connections

Supply and sense

Feed VCC6 before RSC, with SC1, IPK7 and DC8 after it.

Store and recover energy

SE2 feeds the inductor. The diode carries off-state current from ground.

Set the output

The R2/R1 junction drives INV5. The nominal divider predicts 5.208 V.

MC34063A functional cutaway with CT oscillator, current sense, 1.25V reference, comparator, latch, driver and NPN switch. — Functional organization inside an original package drawing; not physical silicon placement.

Explore the circuit

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Compare the output

INV5 is compared with the 1.25 V reference.

Coordinate timing and current

CT3 and IPK7 feed the pulse-control system.

Drive the power transistor

DC8 supplies the driver; SC1 and SE2 expose the main switch terminals.

Selected packagePDIP-8MC34063AP

Physical connections8 pinsPackage-specific numbering

Reference collection8 tables43 parameters & pin functions