TEA2018A

TEA2018A
CURRENT MODE SWITCHING
POWER SUPPLY CONTROL CIRCUIT
.
.
..
.
..
.
DIRECT DRIVE OF THE EXTERNAL
SWITCHING TRANSISTOR
POSITIVE AND NEGATIVE OUTPUT CURRENTS UP TO 0.5 A
CURRENT LIMITATION
TRANSFORMER DEMAGNETIZATION
SENSING
FULL OVERLOAD AND SHORT-CIRCUIT
PROTECTION
PROPORTIONAL BASE CURRENT DRIVING
LOW STANDBY CURRENT BEFORE STARTING (< 1.6 mA)
THERMAL PROTECTION
DESCRIPTION
The TEA2018A is an 8-pin DIP low-cost integrated
circuit designed for the control of switch mode
power supplies.
Due to its current mode regulation, the TEA2018A
facilitates design of power supplies with following
features :
High stability regulation loop
Automatic input voltage feed-forward in discontinuous mode fly-back
Automatic pulse-by-pulse current limitation
Typical applications : Video Display Units, TV sets,
typewriters, microcomputers and industrialapplications
Where synchronization is required, use the
TEA2019. For more details, see application
note AN406/0591
DIP8
(Plastic Package)
ORDER CODE : TEA2018A
..
.
OSCILLATOR
1
8
ERROR AMPLIFIER NON-INVERTING INPUT
GROUND
2
7
DEMAGNETIZATION SENSING
COLLECTOR CURRENT SENSING
3
6
POSITIVE SUPPLY VOLTAGE
NEGATIVE SUPPLY VOLTAGE
4
5
OUTPUT
May 1993
2018A-01.EPS
PIN CONNECTIONS
1/7
TEA2018A
BLOCK DIAGRAM
VCC
6
TEA2018A
DEMAGNETIZATION
SENSING
IS 7
INTERNAL
BIAS
MONITORING
VCC
”Good”
0.1V
Rt
Ct 1
V REF
2.4V
V CC
OSCILLATOR
Undervoltage
Ic
RECOPY
&
FLIP-FLOP
MAXIMUM
DUTY CYCLE
70%
5 OUTPUT
DELAY
500ns
&
1
1
COMPARATOR
8
G ≅ 50
THERMAL
SHUTDOWN
2.4V
3
2
4
I SENSE
GROUND
V CC
2018A-02.EPS
-1V
VOLTAGE
LIMITATION
Parameter
Positive Supply Voltage
Negative Supply Voltage
Peak Output Current (duty cycle < 5%)
Input Current (Pin 3)
Junction Temperature
Operating Ambient Temperature Range
Storage Temperature Range
Value
15
-5
±1
±5
+150
-20, +70
-40, +150
Unit
V
V
A
mA
o
C
o
C
o
C
THERMAL DATA
Symbol
Rth (j-a)
Parameter
Junction-ambient Thermal Resistance
Value
Unit
o
80
C/W
2018A-02.TBL
Symbol
VCC+
VCCIO(peak)
II
Tj
Toper
Tstg
2018A-01.TBL
ABSOLUTE MAXIMUM RATINGS
Symbol
VCC+
VCCVCC(start)
VCC(stop)
2/7
Parameter
Positive Supply Voltage
Negative Supply Voltage
Minimum Positive Supply Voltage required for starting (VCC+ rising)
Minimum Positive Voltage below wich device stops operating (VCC+ falling)
Min.
6.6
-1
4.2
Typ.
8
-3
6
4.9
Max.
15
-5
6.6
5.6
Unit
V
V
V
V
2018A-03.TBL
ELECTRICAL OPERATING CHARACTERISTICS
Tamb = 25oC, potentials referenced to ground (unless otherwise specified) (see test circuit)
TEA2018A
ELECTRICAL OPERATING CHARACTERISTICS
Tamb = 25oC, potentials referenced to ground (unless otherwise specified) (see test circuit)
ton(min)
Parameter
Hysteresis on VCC+ Threshold
Stand-by Supply Current before starting (VCC+ < VCC(start))
Current Limitation Threshold Voltage (Pin 3)
Collector Current Sensing Input Resistance
Demagnetization Sensing Threshold
Demagnetization Sensing Input Current (Pin 7 = 0V)
Maximum Duty Cycle
Error Amplifier Gain
Error Amplifier Input Current (non-inverting input)
Internal Reference Voltage
Min.
0.7
Typ. Max.
1.1
1.6
1
1.6
-1100 -1000 -880
1000
75
100
125
1
60
70
50
2
2.3
2.4
2.5
Unit
V
mA
mV
Ω
mV
µA
%
10-4
V/oC
Reference Voltage Temperature Drift
Oscillator Free-running Period ( R = 59kΩ, C = 1.2nF)
44
48
52
µA
V
µs
o
Oscillator Frequency Drift with Temperature (VCC+ = +8V)
0.05
%/ C
Oscillator Frequency Drift with VCC+ (+8V < VCC+ < +14V)
0.5
%/V
2
µs
Minimum Conducting Time (Ct = 1nF)
2018A-04.TBL
Symbol
∆VCC+
ICC(sb)
Vth(IC)
R (IC)
V7(th)
IS
τmax
AV
II+
VREF
∆VREF
∆T
tOSC
∆fOSC
∆T
∆fOSC
∆VCC
Symbol
VCC+
VCCIO
foper
Parameter
Min.
Positive Supply Voltage
Negative Supply Voltage
Output Current
Operating Frequency
Typ.
8
-3
Max.
0.5
30
Unit
V
V
A
kHz
2018A-05.TBL
RECOMMENDED OPERATING CONDITIONS
TEST CIRCUIT
V8
V7
V6
470Ω
22nF
10Ω
22nF
8
7
6
5
TEA2018A
1
2
1.2nF
1%
3
4
22nF
4.7nF
470nF
100Ω
V1
V3
2018A-03.EPS
59kΩ
1%
V4
3/7
TEA2018A
GENERAL DESCRIPTION
(see application note AN-086)
IC RB
=
IB Re
- Efficient and fast switch-off : When the positive
base drive is removed, 1ms (typically) will elapse
before the application of negative current therefore allowing a safe and rapid collector current
fall.
Operating Principles (Figure 1)
On every period, the beginning of the conduction
time of the transistor is triggered by the fall of the
oscillator sawtooth which acts as clock signal. The
period Tosc is given by : Tosc ≅ 0.66 Ct (Rt + 200)
(Tosc in seconds, Ct in Farad, Rt in Ω)
Safety Functions
- Overload & short-circuit protection : When the
voltage applied to pin 3 exceeds the current
limitation threshold voltage [Vth(Ic)], the output
flip-flop is reset and the transistor is turned off.
The shunt resistor Re must be calculated so as to
obtain the current limitation threshold on pin 3 at
the maximum allowable collector current.
- Demagnetization sensing : This function disables
any new conductioncycle of the transistor as long
as the core is not completely demagnetized.
When not used, pin 7 must be grounded.
- ton(max) : Outside the regulation area and in the
absence of current limitation, the maximum conduction time is set at about 70 % of the period.
- ton(min) : A minimum conducting time is ensured
during each period (see Figure 2)
- Supply voltage monitoring : The TEA2018A will
stop operating if VCC+ on pin 6 falls below the
threshold level VCC(stop)
The end of the conduction time is determined by a
signal issued from comparing the following signals :
a) the sawtooth waveform representing the
collector current of the switching transistor,
sampled across the emitter shunt resistor,
b) the output of the error amplifier.
Base Drive
- Fast turn-on : On each period, a current pulse
ensures fast transistor switch-on.
This pulse performs also the ton(min) function at
the beginning of the conduction.
- Proportional base drive : In order to save power,
the positive base current after the starting pulse
becomes an image of the collector current.
IC
The ratio is programmed as follows Figure 2) :
IB
TEST CIRCUIT
Vi
OUTPUT
FILTER
FLIP-FLOP
OSCILLATOR
S
LOAD
IC
ERROR
AMPLIFIER
Q
VREF
ERROR
SIGNAL
R
COMPARATO R
Re
I C SENSE
OSCILLATOR
SAW-TOOTH
Error signal
I C (sample)
t
FLIP-FLOP
OUTPUT
4/7
t
2018A-04.EPS - 2018A-05.EPS
t
TEA2018A
Figure 2
IC
COLLECTOR
CURRENT I C
0
t
IB
IC
t on(min)
RB
BIAS
CURRENT
5
IB
IB
3
0
Re
RB
Re
IC
t
2018A-06.EPS
TEA2018A
SCHEMATICS OF INPUTS AND OUTPUTS
E
+
V CC+
Is
Vo
Vd + 0.1V
V CC
7.5kΩ
7.5kΩ
50µA
1kΩ
V ref
V CC
Vth H = 0.66 V CC
CC
15kΩ
15kΩ
2kΩ
Vth L = 0.33 V
1kΩ
1kΩ
OSC.
GND
Ic
2018A-07.EPS
DISCH.
V CC -
5/7
TEA2018A
No output pulses are available before the voltage
on pin 6 has reached the threshold level [VCC(start),
VCC rising].
During this time the TEA2018A draws only 1mA
(typically). When the voltage on pin 6 reaches this
threshold, base drive pulses appear.
The energy drawn by these pulses tends to discharge the power supply storage capacitor. However a hysteresis of about 1.1V (typically) (∆ VCC)
is implemented to avoid the device from stopping.
Figure 3 : Normal Start-up Sequence
Figure 4 : tON (min.) versus Ct
Starting Process (Figure 3)
Prior to starting, a low current is drawn from the
high voltage source through a high value resistor.
This current charges the power supply voltage
capacitor of the device.
t
+
V CC
on (min.) ( µs)
12
V CC (start)
10
6V
+
V CC
4.9V
8
6
V CC (stop)
C t (nF)
2
1
2
3
4
5
6
7
8
9
10
2018A-09.EPS
t
2018A-08.EPS
4
TYPICAL APPLICATION
47µF
385V
4 x 1N4007
1N41 48
BYW98-50
68Ω
+12V
100 0µF
15Ω
4.7kΩ
1N414 8
220µF
16V
4.7µF
0.1µF
BYW98-50
+5V
22kΩ
1kΩ
8
4.7kΩ
7
6
5
BA
15 9
RB
8.2Ω
BUV
46 A
0.1µF
2.2kΩ
3W
1kΩ 3W
RF Filter
2 x 12mH
470 0µF
BA
159
TEA2018A
47kΩ
10µF
0.5A
1
2
3
220 VA C
1.2nF
100Ω
150Ω
1nF
1kV
4
3.9V
47µF
Re
6/7
Maximum Power ≅ 30W
Primary Ground
Operating Frequency ≅ 30kHz
Second ary Ground
2018A-10.EPS
1Ω
TEA2018A
PACKAGE MECHANICAL DATA
8 PINS - PLASTIC DIP
I
L
a1
A
e4
b1
B B1
b
E
e
Z
e3
Z
D
5
Dimensions
A
a1
B
b
b1
D
E
e
e3
e4
F
i
L
Z
Min.
4
Millimeters
Typ.
3.32
0.51
1.15
0.356
0.204
Max.
1.65
0.55
0.304
10.92
9.75
7.95
Min.
0.020
0.045
0.014
0.008
Max.
0.065
0.022
0.012
0.430
0.384
0.313
2.54
7.62
7.62
3.18
Inches
Typ.
0.131
0.100
0.300
0.300
6.6
5.08
3.81
1.52
0.125
0260
0.200
0.150
0.060
DIP8.TBL
1
PM-DIP8.EPS
F
8
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for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result
from its use. No licence is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics.
Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all
information previously supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life
support devices or systems without express written approval of SGS-THOMSON Microelectronics.
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