PM6670AS View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'PM6670AS' PDF : 54 Pages View PDF
Device description
Figure 27. Switching frequency selection and VOSC pin
VIN
PPMM66667700AS
R1
VOSC
R2
PM6670AS
7.1.1
The suggested voltage range for VOSC pin is 0.3V to 2V, for better switching frequency
programmability.
Constant-on-time architecture
Figure 28 shows the simplified block diagram of the constant-on-time controller.
The switching regulator of the PM6670AS owns a one-shot generator that ignites the high-
side MOSFET when the following conditions are simultaneously satisfied: the PWM
comparator is high (i.e. output voltage is lower than Vr = 0.9 V), the synchronous rectifier
current is below the current limit threshold and the minimum off-time has expired.
A minimum off-time constraint (300 ns typ.) is introduced to assure the boot capacitor
charge and allow inductor valley current sensing on low-side MOSFET. A minimum on-time
is also introduced to assure the start-up switching sequence.
Once the on-time has timed out, the high side switch is turned off, while the synchronous
rectifier is ignited according to the anti-cross conduction management circuitry.
When the output voltage reaches the valley limit (determined by internal reference
Vr = 0.9 V), the low-side MOSFET is turned off according to the anti-cross conduction logic
once again, and a new cycle begins.
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Doc ID 14436 Rev 2
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