PM6680ATR STMicroelectronics, PM6680ATR Datasheet - Page 21

• Manufacturer Part Number: PM6680ATR
• Description: IC CTRLR DUAL STEP DOWN 32VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6680ATR

• Applications: Controller, Embedded Computer System
• Voltage - Input: 6 ~ 36 V
• Number Of Outputs: 2
• Voltage - Output: 0.9 ~ 5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• For Use With: 497-6379 - BOARD EVALUATION FOR PM6680A497-6378 - BOARD EVALUATION FOR PM6680497-6425 - BOARD EVAL BASED ON PM6680A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6896-2; PM6680ATR

PM6680A
7.3
Output ripple compensation and loop stability
In a classic constant on time control, the system regulates the valley value of the output
voltage and not the average value, as shown in
voltage ripple is source of a DC static error.
To compensate this error, an integrator network can be introduced in the control loop, by
connecting the output voltage to the COMP1/COMP2 (for the OUT1 and OUT2 sections
respectively) pin through a capacitor C
Figure 30.
The integrator amplifier generates a current, proportional to the DC errors between the FB
voltage and Vr, which decreases the output voltage in order to compensate the total static
error, including the voltage drop on PCB traces. In addition, C
output ripple. In steady state, the voltage on COMP1/COMP2 pin is the sum of the reference
voltage Vr and the output ripple (see
reaches Vr, a fixed Ton begins and the output increases.
For example, we consider Vout = 5 V with an output ripple of ∆V = 50 mV. Considering C
>> C
an AC path for the output voltage ripple. Then the COMP pin ripple is a replica of the output
ripple, with a DC value of Vr + 25 mV = 925 mV.
For more details about the output ripple compensation network, see the
Closing the integrator loop on page 35
FILT
, the C
Circuitry for output ripple compensation
INT
DC voltage drop VC
Figure
INT
INT
in the Design guidelines.
is about 5 V -Vr + 25 mV = 4.125 V. C
as in
30). In fact when the voltage on the COMP pin
Figure
Figure 28
30.
In this condition, the output
INT
provides an AC path for the
Device description
Chapter 9.6:
INT
assures
21/48
INT