PM6670AS STMicroelectronics, PM6670AS Datasheet - Page 22

• Manufacturer Part Number: PM6670AS
• Description: IC CTLR DDR2/3 MEM PS VFQFPN-24
• Manufacturer: STMicroelectronics

Specifications of PM6670AS

• Applications: Memory, DDR2/DDR3 Regulator
• Current - Supply: 800µA
• Voltage - Supply: 4.5 V ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-VFQFN, 24-VFQFPN
• For Use With: 497-8412 - BOARD EVAL PM6670AS DDR2/3497-8411 - BOARD EVAL PM6670S DDR2/3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Device description
7.1.1
22/53
Figure 27. Switching frequency selection and VOSC pin
The suggested voltage range for VOSC pin is 0.3V to 2V, for better switching frequency
programmability.
Constant-on-time architecture
Figure 28
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.
shows the simplified block diagram of the constant-on-time controller.
Doc ID 14436 Rev 2
R2
R1
VIN
VOSC
PM6670AS
PM6670
PM6670AS