These versatile SMPS ICs comprise digital and analog functions which are required to
design high-quality flyback, single-ended, and push-pull converters in normal, half-
bridge and full-bridge configurations. The components can also be used in single-ended
voltage multipliers and speed-controlled motors. Malfunctions in electrical operation are
recognized by the integrated op amps which activate protective functions.
Type
Ordering Code
Package
s
TDA 4714 C
Q67000-A8312
P-DIP-14-1
s
TDA 4716 C
Q67000-A8313
P-DIP-16-1
s
Not for new design
IC for Switched-Mode Power Supplies (SMPS)
Bipolar IC
P-DIP-14-1
P-DIP-16-1
Features
q
Push-pull outputs (open collector)
q
Double pulse suppression
q
Dynamic current limitation
q
Overvoltage protection
q
IC undervoltage protection
q
Reference voltage source
q
Reference overload protection
q
Soft start
q
Feed-forward control
q
Operational amplifier (TDA 4716 C)
Semiconductor Group
1
09.94
TDA 4714 C
TDA 4716 C
TDA 4714 C
TDA 4716 C
Semiconductor Group
2
Pin Configurations
(top view)
TDA 4714 C
TDA 4716 C
TDA 4714 C
TDA 4716 C
Semiconductor Group
3
Pin Definitions and Functions
(TDA 4714 C)
Pin
Symbol
Function
1
2
V
REF
+
V
S
Reference voltage
Supply voltage
3
4
Q2
Q1
Output Q2
Output Q1
5
C
soft start
Soft start
6
7
R
T
C
T
VCO
R
T
VCO
C
T
8
9
R
R
C
R
Ramp generator
R
R
Ramp generator
C
R
10
I COMP
Input comparator
11
I OV
Input overvoltage
12
13
I
DYN
+
I
DYN
Dynamic current
limitation ()
Dynamic current
limitation (+)
14
GND
Ground
Pin Definitions and Functions
(TDA 4716 C)
Pin
Symbol
Function
1
2
V
REF
V
S
Reference voltage
V
REF
Supply voltage
V
S
3
4
Q2
Q1
Output Q2
Output Q1
5
C
soft start
Soft start
6
7
R
T
C
T
VCO
R
T
VCO
C
T
8
9
R
R
C
R
Ramp generator
R
R
Ramp generator
C
R
10
11
12
Q op amp
I op amp
+ I op amp
Operational amplifier
output
Operational amplifier
input ()
Operational amplifier
input (+)
13
I OV
Input overvoltage
14
15
I
DYN
+
I
DYN
Dynamic current
limitation ()
Dynamic current
limitation (+)
16
GND
Ground
TDA 4714 C
TDA 4716 C
Semiconductor Group
4
Circuit Description
The following is a description of the individual functional units and their interaction.
Voltage Controlled Oscillator (VCO)
The VCO generates a sawtooth voltage. The duration of the falling edge is determined
by the value of
C
T
. The duration of the rising edge of the waveform and, therefore,
approximately the frequency, is determined by the value of
R
T
. During the fall time, the
VCO provides a trigger signal for the ramp generator, as well as an L signal for a number
of IC parts to be controlled.
Ramp Generator
The ramp generator is triggered by the VCO and oscillates at the same frequency. The
duration of the falling edge of the ramp generator waveform is to be shorter than the fall
time of the VCO. To control the pulse width at the output, the voltage of the rising edge
of the ramp generator signal is compared with a DC voltage at comparator K2. The slope
of the rising edge of the ramp generator signal is controlled by the current through
R
R
.
This offers the possibility of an additional, superimposed control of the output duty cycle.
This additional control capability, called "feed-forward control", is utilized to compensate
for known interference such as ripple on the input voltage.
Push-Pull Flipflop
The push-pull flipflop is switched by the falling edge of the VCO. This ensures that only
one output of the two push-pull outputs is enabled at a time.
Comparator K2
The two plus inputs of the comparator are switched such that the lower plus level is
always compared with the level of the minus input. As soon as the voltage of the rising
sawtooth edge exceeds the lower of the two plus levels, both outputs are disabled via
the pulse turn-OFF flipflop. The period during which the respective, active output is low
can be infinitely varied. As the frequency remains constant, this process corresponds to
a change in duty cycle.
Operational Amplifier K1 (TDA 4716 C)
The op amp K1 is a high-quality amplifier. Fluctuations in the output voltage of the power
supply are amplified by K1 and applied to the free positive input of comparator K2.
Variations in output voltage are, in this way, converted to a corresponding change in
output duty cycle. K1 has a common-mode input voltage range between 0 V and + 5 V.
TDA 4714 C
TDA 4716 C
Semiconductor Group
5
Pulse Turn-OFF Flipflop
The pulse turn-OFF flipflop enables the outputs at the start of each half cycle. If an error
signal from comparator K7 or a turn-off signal from K2 is present, the outputs will
immediately be switched off.
Comparator K3
Comparator K3 limits the voltage of capacitance
C
soft start
(and also at K2!) to a maximum
of + 5 V. The voltage at the ramp generator output may, however, rise to 5.5 V. With a
corresponding slope of the rising ramp generator edge, the duty cycle can be limited to
a desired maximum value.
Comparator K4
The comparator has its switching threshold at 1.5 V and sets the error flipflop with its
output if the voltage at capacitance
C
soft start
is below 1.5 V. However, the error flipflop
accepts the set signal only if no reset pulse (error) is applied. In this way the outputs
cannot be turned on again as long as an error signal is present.
Soft Start
The lower one of the two voltages at the plus inputs of K2 is a measure for the duty cycle
at the output. At the instant of turning on the component, the voltage at capacitor
C
soft start
equals 0 V. As long as no error is present, this capacitor is charged with a current of 6
A
at the maximum value of 5 V. In case of an error,
C
soft start
is discharged with a current of
2
A. A set signal is pending at the error flipflop below a charge of 1.5 V and the outputs
are enabled if no reset signal is pending simultaneously. As the minimum ramp
generator voltage, however, is 1.8 V, the duty cycle at the outputs is actually increased
slowly and continuously not before the voltage at
C
soft start
exceeds 1.8 V.
Error Flipflop
Error signals, which are led to input R of the error flipflop cause an immediate disabling
of the outputs, and after the error has been eliminated, the component to switch on again
by the soft start.
Comparator K5, K8,
V
REF
Overcurrent Load
These are error detectors which cause immediate disabling of the outputs via the error
flipflop when an error occurs. After elimination of the error, the component switches on
again by the soft start.
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