EVALA5972D STMicroelectronics, EVALA5972D Datasheet - Page 8

• Manufacturer Part Number: EVALA5972D
• Description: Power Management Modules & Development Tools EVAL BOARD A5972 Auto Grade
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of EVALA5972D

• Input Voltage: 4.4 V to 36 V
• Output Voltage: 1.235 V to 35 V
• Board Size: 23 mm x 20 mm
• Product: Power Management Modules
• Supply Current: 2 A
• Dimensions: 23 mm x 20 mm
• For Use With/related Products: AN1517
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Functional description
2.5
2.6
8/29
Due to this reduction of the ON time, the output voltage decreases.
Since the minimum switch ON time (necessary to avoid a false over-current signal) is too
short to obtain a sufficiently low duty cycle at 250 kHz, the output current, in strong over-
current or short-circuit conditions, could increase again. For this reason the switching
frequency is also reduced, thus keeping the inductor current under its maximum threshold.
The Frequency Shifter
voltage decreases (due to the reduced duty cycle), the switching frequency decreases also.
Figure 7.
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 2.
The error amplifier output is compared with the oscillator sawtooth to perform PWM control.
PWM comparator and power stage
This block compares the oscillator sawtooth and the error amplifier output signals
generating 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 a first approach, it appears that
Minimum sink/source voltage
Output voltage swing
Low frequency gain
Transconductance
Input bias current
Description
Current limitation circuitry
Uncompensated error amplifier characteristics
A1/A2=95
(Figure
DRIVER
VCC
OUT
I
OFF
6) functions based on the feedback voltage. As the feedback
PWM
A1
RSENSE
A2
I
1500 µA/300 µA
0.4 V/3.65 V
2300 µS
Values
2.5 µA
65 dB
I
NOT
AM00008v1
RTH
I
L
AN1517