R5975D Datasheet, PDF (15/47 Pages) STMicroelectronics – Up to 3 A step-down switching regulator for aerospace applications

R5975D
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Figure 6. Current limitation circuitry
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Functional description
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5.5
Error amplifier
The voltage error amplifier is the core of the loop regulation. It is a transconductance
operational amplifier whose non inverting input is connected to the internal voltage
reference (1.235 V), while the inverting input (FB) is connected to the external divider or
directly to the output voltage. The output (COMP) is connected to the external
compensation network. The uncompensated error amplifier has the following
characteristics:
Table 5. Uncompensated error amplifier characteristics
Description
Values
Transconductance
Low frequency gain
2300 µS
65 dB
Minimum sink/source voltage
1500 µA/300 µA
Output voltage swing
Input bias current
0.4 V/3.65 V
2.5 µA
The error amplifier output is compared to the oscillator sawtooth to perform PWM control.
5.6
PWM comparator and power stage
This block compares the oscillator sawtooth and the error amplifier output signals to
generate the PWM signal for the driving stage.
The power stage is a highly critical block, as it functions to guarantee a correct turn-on and
turn-off of the PDMOS. The turn-on of the power element, or more accurately, the rise time
of the current at turn-on, is a very critical parameter. At the first approach, it appears that the
faster the rise time, the lower the turn-on losses.
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