November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

GENERAL DESCRIPTION

The TDA8380A is an integrated circuit intended for use as a control circuit in low-cost switched mode power supplies for
television, monitors and small industrial equipment. The TDA8380A operates using duty factor regulation in the fixed
frequency mode.

Features

A low-current initialization circuit (maximum 150

A) which can be switched off

A bandgap reference generator

Circuitry for slow-start combined with an accurate setting of the maximum duty factor (D

max

)

Programmable low supply voltage protection with one default value

High supply protection circuitry

Error amplifier with a transfer characteristic generator (TCG)

Protection against open- and short-circuited feedback loop

An overload voltage foldback

Primary current protection circuitry for both cycle-by-cycle and trip mode

Protection against transformer saturation

A direct drive output stage (sink current 2.5 A, source current 0.75 A)

Anti-double pulse logic

Protected against damage as a result of a short-circuited high-voltage transistor

RC oscillator with synchronization input

QUICK REFERENCE DATA

PACKAGE OUTLINE

16-lead DIL; plastic (SOT38); SOT38-1 ; 1996 November 18.

PARAMETER

SYMBOL

MIN.

TYP.

MAX.

UNIT

Supply voltage

Supply current

Output pulse repetition frequency range

100

kHz

Operating ambient temperature range

amb

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

PINNING

Emitter of output source transistor

Collector of output source transistor

DEM

Demagnetization sense input

CCmin

Minimum V

threshold setting

Supply voltage

ref

Reference current setting

Feedback input

STAB

Output error amplifier

DUTY

Pulse width modulator input

OSC

Oscillator capacitor

SYNC

Synchronization input

Maximum duty factor (D

max

) setting plus slow-start

CURR

Input current protection

Ground

Emitter of output sink transistor

Collector of output sink transistor

Fig.2 Pinning diagram.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

FUNCTIONAL DESCRIPTION

The TDA8380A is a control circuit which generates the pulses required to drive the switching transistor in a switched
mode power supply (SMPS).

Supply

This device is intended to be used on the primary side of the power supply and can be supplied via a take-over (auxiliary)
winding on the transformer.

The device is initialized via a high value resistor connected between the rectified mains voltage and the device's supply
pin (pin 5), which causes the capacitor connected to this pin to charge slowly. When the voltage exceeds the initialization
level (typically 17 V) the device will start up and the duty cycle will be slowly increased by the slow-start circuit. After a
short period the take-over winding will supply the device. The value of the resistor is normally defined by the time taken
to charge the capacitor.
A one second delay between switching on and operation of the power supply is acceptable in most cases.

The operating voltage range is from 9 to 20 V. The supply pin is protected by a 23 V Zener diode. The supply protection
circuit is activated once the Zener diode is conducting. The slow-start procedure begins after initialization, until then the
output is off. The current drawn by the device during the initialization period is less than 150

When the supply voltage falls below the minimum trip level, the device switches off and the start-up procedure is
repeated. The minimum voltage supply threshold setting (V

CCmin

) can be set externally with a resistor connected between

the V

CCmin

pin (pin 4) and ground (pin 14) (see Fig.3).

CCmin

can be set between 8.4 V (an internally fixed overriding protection level) and 17 V by means of an external resistor

connected to pin 4.

When choosing the initialization and minimum supply voltages the following should be taken into account:

The difference between the two voltages should be large enough to enable a supply voltage dip during start-up.

The value of the minimum supply voltage should be high enough to ensure that the high-voltage transistor is correctly
driven. A high protection level makes it possible to have a large resistor value in series with the base drive.

For battery line input operation, the V

CCmin

pin is connected to V

, the start-up circuit is then inhibited and the device

starts operating when V

exceeds the 8.4 V protection level (this level has a hysteresis of approximately 50 mV). The

device draws current continuously under these conditions.

Fig.3 Trip level setting of minimum V

protection level.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

Reference block

A bandgap based reference generates a stabilized voltage of 7 V to supply most of the device's internal circuits, this
decreases chip size and increases reliability. The only circuits connected to V

are:

The initialization circuit

The output circuitry

The series transistor of the stabilized voltage

By means of a resistor (R

) connected to the I

ref

input a reference current is defined which determines six other device

settings.

Part of the reference current is used to charge the oscillator capacitor (C

), therefore, the charging time is proportional

to R

. The maximum duty factor (D

max

) is set by the resistor connected to pin 12 (R

) and is defined by the ratio

. The minimum supply voltage (pin 5) set by the resistor (R

) at input V

CCmin

is defined by: 4/6

Oscillator

The oscillator capacitor is charged and discharged between the high and low voltage levels as defined by the bandgap
reference (high voltage typically 5 V and low voltage typically 1.4 V). The charge current is 1/6 of the reference current,
the discharge current having the same value as the reference current. The period is therefore defined by 10

The oscillator flyback pulse is used to set the bistable in the output logic, however the output remains low until the positive
ramp starts (see Fig.4). The oscillator can be synchronized by means of the SYNC pin. When this pin is connected to
V

, the oscillator is free running. When it is between 0.85 and 5.6 V, the oscillator stops at the low voltage level prior to

the next positive ramp.

Fig.4 Oscillator levels.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

Synchronization

The synchronisation input (pin 11) can be driven by either an optocoupler or a loosely coupled pulse transformer.

Figure 5 illustrates synchronization using the 0.85 V threshold and a digital signal connected to the SYNC input (for
example, an optocoupler between pin 11 and V

); the duty factor of the pulse is not very important. The oscillator starts

at the first negative going edge of the sync. signal after the low voltage level has been reached. The synchronization
frequency must be lower than the free running frequency. Synchronization must never affect the period time as this will
corrupt the setting of the maximum duty factor.

In Fig.6 the disabling threshold (5.6 V) is used for synchronization. In this case the oscillator starts at the positive going
edge of the sync. signal.

Fig.5 DC coupled synchronization using the 0.85 V level.

Fig.6 DC coupled synchronization using the 5.6 V level.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

Figure 7 illustrates synchronization using a pulse transformer. Internal circuitry causes a DC shift which informs the
device that synchronization pulses are present (spikes around 0 V at the output of the pulse transformer) or not present
(DC 0 V at the output of the pulse transformer). When synchronization is not used the SYNC pin must be connected to
V

, it must not be connected directly to ground or left open.

Fig.7 Synchronization using a pulse transformer.

Synchronization pulses present.

Synchronization pulses not present.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

Error amplifier

The error amplifier compares the feedback voltage of the SMPS with a reference voltage (nominally 2.5 V). The amplifier
output at pin 8 enables gain setting. The amplifier is stable for a gain greater than 20 dB.

The output of the error amplifier is not internally connected to the Pulse Width Modulator (PWM). One input to the PWM
is available at the DUTY input (pin 9) via the Control Slicing Level (CSL) circuit. Normally the STAB and DUTY pins are
connected together, but direct driving of pin 9 via an optocoupler from the secondary side is also possible. A type of
current mode control can be achieved by mixing the STAB signal with the primary current signal before applying it to the
DUTY input.

The feedback (FB) input (pin 7) is used as the input to the Transfer Characteristic Generator (TCG) circuit which ensures
well defined duty factors at low FB voltages; a voltage foldback is an inherent characteristic. In Fig.8, the duty factor is
shown as a function of the voltages at the FB, DUTY and SS inputs. The input which gives the lowest duty factor overrides
the others.

The left hand curve is passed through during a slow-start (via the slow-start input pin 12) when the duty cycle slowly
increases linearly with respect to V

. The right-hand curve is passed through at start-up. The FB voltage slowly

increases from zero and the duty factor, starting at 12%, increases until the maximum duty factor (D

max

) is reached. A

few hundred millivolts later, the FB voltage reaches the start of the regulation curve which is at approximately 2.5 V. The
plateau area between reaching D

max

and starting the regulation curve is kept as small as possible (typically 200 mV).

Due to the characteristics of the TCG, and the fact that an open FB input results in a low voltage at the FB input, open-
and short-circuit feedback loops will result in low duty factors. When DC feedback is used across the error amplifier, the
current capability of the error amplifier must be considered when determining the feedback resistor value.

When the input to the PWM (pin 9) is driven by an optocoupler, the TCG can be used when a rough primary voltage is
applied to the FB input. In this situation an open feedback loop will cause an increase in the FB voltage as the duty factor
rises to its maximum. As soon as the FB voltage exceeds the reference by 0.7 V, the slow-start is triggered.

Fig.8 The duty factor as a function of the FB, SS and DUTY voltages.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

Demagnetization sense circuit

To enable the SMPS to be kept in the non-continuous mode, an input is available which delays switch-on of the
high-voltage transistor until the transformer currents have decayed to zero. This is an effective way of avoiding
transformer saturation. The waveforms illustrated by Fig.9 show demagnetization with respect to the application diagram
of Fig.13.

As long as the voltage of the take-over (auxiliary) winding (also used for supplying the device) is above 0.6 V (V

) the

output will be prevented from switching on.

Over-current protection

The over-current protection circuit (pin 13) senses the voltage across resistor R

(see Fig.13), which reflects the primary

current. This generated voltage is negative-going as the emitter of the high-voltage power transistor is grounded (this
circuit arrangement provides the IC with the best safeguard against a possible collector-emitter short-circuit in the power
transistor). At pin 13, the negative voltage signal is shifted to a positive level by a voltage across resistor R

. This voltage

is set by the reference current at pin 13 and is defined by resistor R

at the I

ref

input (pin 6) and = 1/6

ref

Therefore V

shift

R 13

) = V

ref

or nominal 0.416

(V).

The positive current monitor voltage at pin 13 is compared with two voltage levels: the first level = 0.2 V and the second
level = 0 V (see Fig.10).

The first trip level only switches off the high-voltage transistor for a cycle and puts the SMPS in a continuous
cycle-by-cycle current protection mode.

The second trip level is only activated when the primary current rise is very fast which can occur during a short-circuited
output. In this mode the high-voltage transistor is quickly switched off and the slow-start procedure is activated.

The difference between the first and second primary current peak levels is set by R

= 0.2/R

The absolute peak values are set by R

and R

= 0.416

= (0.416

)

0.2

Fig.9 Demagnetization function.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

Slow-start circuit

A slow-start occurs:

At Switch-on of the SMPS

After a current trip as described in the section Over-current protection

After a low or high V

trip.

The capacitor at the SS input is discharged and the slow-start bistable is reset when the voltage at the SS input falls
below 0.5 V after which the circuit is ready for a slow-start. The dead time (during which the capacitor at the SS input is
being charged to the 1.4 V lower level of the sawtooth) before duty cycle regulation starts is minimal. The SS input can
also be used for D

max

setting by connecting a resistor to ground. The voltage across this resistor is then limited to

1/6

ref

Output stages

The output stage consists of two NPN darlington transistors, their collector and emitter connected to separate pins (see
Fig.13). The top transistor is capable of sourcing a maximum of 0.75 A to the high-voltage transistor while the bottom
transistor can sink peak currents up to 2.5 A.

For low currents up to 10 mA, the saturation voltage of the sink darlington transistor is similar to that of a single transistor
(see Fig.11). During switching of this transistor dV/dt is internally limited to reduce interference.

Care should be taken with the external wiring of the output pins to avoid oscillation or interference due to parasitic
inductance and wire resistance.

During start-up a small current flows from V

to E2 to precharge the series capacitor at the output (see Fig.13).

Fig.10 Current protection.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

RATINGS

Limiting values in accordance with the Absolute Maximum System (IEC 134)

THERMAL RESISTANCE

PARAMETER

SYMBOL

MIN.

TYP.

MAX.

UNIT

Voltage

pin 5 (V

)

0.5

pins 1, 2, 4 and 16

0.5

pins 3 and 13

0.5

pins 7 and 9

0.5

6.5

pin 11

0.6

Currents

pins 5 (V

)

pin 1

0.75

pin 2

0.75

pins 3, 4, 6 to 8 and 10 to 12

pin 13

200

pin 15

2.5

pin 16

2.5

Total power dissipation

tot

see Fig.12

Operating ambient temperature range

(for dissipation

1 W)

amb

Storage temperature range

stg

150

From junction to ambient (in free air)

th j

a(max)

55 K/W

Fig.12 Power derating curve.

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

CHARACTERISTICS

= 14 V; T

amb

= 25

C; reference resistor = 5 k

unless otherwise specified

PARAMETER

CONDITIONS

SYMBOL

MIN.

TYP.

MAX.

UNIT

Supply

Supply voltage

Supply initialization level

High voltage protection

Internal fixed minimum

protection level

7.9

8.4

8.9

Hysteresis

Supply current

operational

before initialization

100

150

Reference current (pin 4)

note 1

/5.7

/6.4

Trigger level V

CCmin

setting

3.6V

3.8V

4.2V

Clamp voltage

at 20 mA

21.5

23.5

25.5

Reference (pin 6)

Reference voltage

ref

2.4

2.5

2.6

Current range

ref

200

800

Reference voltage over

range

ref

Error amplifier

Error amplifier threshold

= 8.5 to 20 V

2.4

2.5

2.6

Input current

Sink current output

at 1.2 V

Source current output

at 5.5 V

100

130

Open loop gain

100

Unity gain bandwidth

MHz

Input DUTY current

note 1

/5.7

/6.3

High FB protection level

2.95

3.1

3.25

Temperature coefficient of

error amplifier threshold

/dT

100

TCG function (see Fig.8)

Transfer characteristics

dD/dV

%/V

Minimum duty factor

min

Plateau width

200

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

Slow-start function

Transfer characteristics

dD/dV

23.8

%/V

Input current

note 1

/5.7

/6.3

Sink current during faults

at 0.5 V

Internally fixed maximum

duty factor

max

Clamp current

at V

= 0.5 V

Output stage

Source transistor

Voltage drop with respect

to V

at 0.75 A

Pull-up current

= 15 V

100

Operating current range

0.75

Sink transistor (see Fig.11)

Saturation voltage

at 2.5 A

at 1 A

1.5

at 10 mA

0.3

Leakage current

= 20 V

Falling edge

/dt

0.2

V/ns

Operating current range

Peak

2.5

Average

250

Oscillator

High level voltage

Low level voltage

1.4

Charge current

note 1

/5.7

/6.3

Frequency range

100

kHz

Frequency

= 5 k

= 680 pF

28.5

kHz

Temperature coefficient of

the frequency

df/dT

100

PARAMETER

CONDITIONS

SYMBOL

MIN.

TYP.

MAX.

UNIT

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

Note to the characteristics

1. Over the current range of I

; 200 to 800

Synchronization

Minimum synchronization

pulse width

0.5

Switching threshold

0.7

0.85

0.9

Input current

2.5

5.0

7.5

Disabling threshold

4.2

5.6

6.0

Input voltage

700

390

550

Demagnetization input

Switching voltage level

615

645

675

Switching current level

Current range of clamp

circuits

Clamp level positive

at 10 mA

950

Clamp level negative

10 mA

800

Temperature coefficient

1.9

mV/K

Current protection

Input current

note 1

/5.7

/6.3

First threshold

190

200

210

Second threshold

Delay to switch output via

pulse at pin 13

level 1

from 300 mV to
100 mV;
I

= 500 mA

350

Delay to switch output via

pulse at pin 13

level 2

from 300 mV to

200 mV;

= 500 mA

300

500

First threshold including

(12 k

)

= 5 k

800

Threshold for open pin

detection

3.5

PARAMETER

CONDITIONS

SYMBOL

MIN.

TYP.

MAX.

UNIT

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

PACKAGE OUTLINE

UNIT

max.

REFERENCES

OUTLINE

VERSION

EUROPEAN

PROJECTION

ISSUE DATE

IEC

JEDEC

EIAJ

inches

DIMENSIONS (inch dimensions are derived from the original mm dimensions)

SOT38-1

92-10-02
95-01-19

min.

max.

1.40
1.14

0.055
0.045

0.53
0.38

0.32
0.23

21.8
21.4

0.86
0.84

6.48
6.20

0.26
0.24

3.9
3.4

0.15
0.13

0.254

2.54

7.62

0.30

8.25
7.80

0.32
0.31

9.5
8.3

0.37
0.33

2.2

0.087

4.7

0.51

3.7

0.15

0.021
0.015

0.013
0.009

0.01

0.10

0.020

0.19

050G09

MO-001AE

(e )

seating plane

pin 1 index

10 mm

scale

Note

1. Plastic or metal protrusions of 0.25 mm maximum per side are not included.

(1)

DIP16: plastic dual in-line package; 16 leads (300 mil); long body

SOT38-1

November 1993

Philips Semiconductors

Product specification

Control circuit for switched mode power supplies

TDA8380A

SOLDERING

Introduction

There is no soldering method that is ideal for all IC packages. Wave soldering is often preferred when through-hole and
surface mounted components are mixed on one printed-circuit board. However, wave soldering is not always suitable for
surface mounted ICs, or for printed-circuits with high population densities. In these situations reflow soldering is often
used.

This text gives a very brief insight to a complex technology. A more in-depth account of soldering ICs can be found in our
"IC Package Databook" (order code 9398 652 90011).

Soldering by dipping or by wave

The maximum permissible temperature of the solder is 260

C; solder at this temperature must not be in contact with the

joint for more than 5 seconds. The total contact time of successive solder waves must not exceed 5 seconds.

The device may be mounted up to the seating plane, but the temperature of the plastic body must not exceed the
specified maximum storage temperature (T

stg max

). If the printed-circuit board has been pre-heated, forced cooling may

be necessary immediately after soldering to keep the temperature within the permissible limit.

Repairing soldered joints

Apply a low voltage soldering iron (less than 24 V) to the lead(s) of the package, below the seating plane or not more
than 2 mm above it. If the temperature of the soldering iron bit is less than 300

C it may remain in contact for up to

10 seconds. If the bit temperature is between 300 and 400

C, contact may be up to 5 seconds.

DEFINITIONS

LIFE SUPPORT APPLICATIONS

These products are not designed for use in life support appliances, devices, or systems where malfunction of these
products can reasonably be expected to result in personal injury. Philips customers using or selling these products for
use in such applications do so at their own risk and agree to fully indemnify Philips for any damages resulting from such
improper use or sale.

Data sheet status

Objective specification

This data sheet contains target or goal specifications for product development.

Preliminary specification

This data sheet contains preliminary data; supplementary data may be published later.

Product specification

This data sheet contains final product specifications.

Limiting values

Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress above one or
more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation
of the device at these or at any other conditions above those given in the Characteristics sections of the specification
is not implied. Exposure to limiting values for extended periods may affect device reliability.

Application information

Where application information is given, it is advisory and does not form part of the specification.

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