MC34065–H, L MC33065–H, L

9

MOTOROLA ANALOG IC DEVICE DATA

Figure 17. External Clock Synchronization

Figure 18. External Duty Cycle Clamp and

Multi–Unit Synchronization

–

+

R

220pF

RT

R

R

15

1

3

2

4

5

CT

External

Sync

Input

Bias

Osc.

20k

EA1

1.0V

2R

The external diode clamp is required if the negative Sync current

is greater than –5.0 mA.

–

+

–

+

–

+

6

5

2

C

RB

MC1455

R

S

Q

3

7

4

8

RA

Vref

15

1

3

2

4

5

To additional MC34065s

2R

R

1.0V

Osc.

Bias

R

R

5.0k

5.0k

5.0k

1

EA1

f =

1.08

(RA + RB)C

Dmax Drive Output 1 =

RB

RA + RB

Dmax Drive Output 2 =

RA

RA + RB

20k

PIN FUNCTION DESCRIPTION

Pin

Function

Description

1

Sync Input

A narrow rectangular waveform applied to this input will synchronize the oscillator. A dc voltage

within the range of 2.4 V to 5.5 V will inhibit the oscillator.

2

CT

Timing capacitor CT connects from this pin to ground setting the free–running oscillator frequency

range.

3

RT

Resistor RT connects from this pin to ground precisely setting the charge current for CT. RT must be

between 4.0 k and 16 k.

4

Voltage Feedback 1

This pin is the inverting input of Error Amplifier 1. It is normally connected to the switching power

supply output through a resistor divider.

5

Compensation 1

This pin is the output of Error Amplifier 1 and is made available for loop compensation.

6

Current Sense 1

A voltage proportional to the inductor current is connected to this input. PWM 1 uses this information

to terminate conduction of output switch Q1.

7

Drive Output 1

This pin directly drives the gate of a power MOSFET Q1. Peak currents up to 400 mA are sourced

and sunk by this pin.

8

Gnd

This pin is the control circuitry ground return and is connected back to the source ground.

9

Drive Gnd

This pin is a separate power ground return that is connected back to the power source. It is used to

reduce the effects of switching transient noise on the control circuitry.

10

Drive Output 2

This pin directly drives the gate of a power MOSFET Q2. Peak currents up to 400 mA are sourced

and sunk by this pin.

11

Current Sense 2

A voltage proportional to inductor current is connected to this input. PWM 2 uses this information to

terminate conduction of output switch Q2.

12

Compensation 2

This pin is the output of Error Amplifier 2 and is made available for loop compensation.

13

Voltage Feedback 2

This pin is the inverting input of Error Amplifier 2. It is normally connected to the switching power

supply output through a resistor divider.

14

Drive Output 2 Enable

A logic low at this input disables Drive Output 2.

15

Vref

This is the 5.0 V reference output. It can provide bias for any additional system circuitry.

16

VCC

This pin is the positive supply of the control IC. The minimum operating voltage range after startup is

11 V to 15.5 V for the –H suffix, 8.2 V to 9.5 V for the –L suffix.