a5975d STMicroelectronics, a5975d Datasheet - Page 15

• Manufacturer Part Number: a5975d
• Description: Up To 3 A Step-down Switching Regulator For Automotive Applications
• Manufacturer: STMicroelectronics

A5975D
Figure 7.
5.5
5.6
Current limitation circuitry
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.
The error amplifier output is compared to the oscillator sawtooth to perform PWM control.
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.
Transconductance
Low frequency gain
Minimum sink/source voltage
Output voltage swing
Input bias current
Description
Uncompensated error amplifier characteristics
Doc ID 018760 Rev 1
1500 µA/300 µA
0.4 V/3.65 V
2300 µS
Values
2.5 µA
65 dB
Functional description
15/50