TDA16833 查看數據表（PDF） - Infineon Technologies
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TDA16833 Datasheet PDF : 21 Pages
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TDA 16831-4
Circuit Description
The TDA 16831-4 is a current mode pulse
width modulator with integrated sense
CoolMOS transistor. It fulfills the
requirements of minimum external control
circuitry for a flyback application.
Current mode control means that the
current through the MOS transistor is
compared with a reference signal derived
from the output voltage of the flyback
application. The result of that comparison
determines the on time of the MOS
transistor.
To minimize external circuitry the sense
resistor which gives information about
MOS current is integrated. The oscillator
resistor and capacitor which determine the
switching frequency are integrated, too.
Special efforts have been made to
compensate temperature dependency and
to minimize tolerances of this resistor.
The circuit in detail: (see Figure 3)
Start Up Circuit (uvlo)
Uvlo is monitoring the external supply
voltage VCC. When VCC is exceeding the on
threshold VCCH = 12 V, the bandgap, the
bias circuit and the soft start circuit are
switched on. When VCC is falling below the
off-threshold VCCL = 9 V the circuit is
switched off. During start up the current
consumption is about 30 µA.
Bandgap (bg)
The bandgap generates an internal very
accurate reference voltage of 5.5 V to
supply the internal circuits.
Current Source (bias)
The bias circuit provides the internal
circuits with constant current.
Oscillator (osc)
The oscillator is generating a frequency
twice the switching frequency
fswitch = 100 kHz. Resistor, capacitor and
current source which determine the
frequency are integrated. The charging
and discharging current of the
implemented oscillator capacitor is
internally trimmed, in order to achieve a
very accurate switching frequency.
Temperature coefficient of switching
frequency is very low ( see page 19).
Divider Flip Flop (tff)
Tff is a flip flop which divides the oscillator
frequency by one half to create the
switching frequency. The maximum duty
cycle is set to Dmax = 0.5.
Current Sense Amplifier (pwmop)
The positive input of the pwmop is applied
to the internal sense resistor. With the
internal sense resistor (Rsense) the sensed
current coming from the CoolMOS is
converted into a sense voltage. The sense
voltage is amplified with a gain of 32 dB.
The amplified sense voltage is connected
to the negative input of the pwm
comparator. Each time when the CoolMOS
transistor is switched on, a current spike is
superposed to the true current information.
To eliminate this current spike the sense
voltage is smoothed via an internal resistor
capacitor network with a time constant of
Td1 = 100 ns. This is the first leading edge
blanking and only a small spike is left. To
reduce this small spike the current sense
amplifier is creating a virtual ramp at the
output. This is done by a second resistor
capacitor network with Td2 = 100 ns and an
op-offset of 0.8 V which is seen at the
output of the amplifier. When gate drive is
Data Sheet
6
1999-12-10
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