PM6670S STMicroelectronics, PM6670S Datasheet - Page 22

• Manufacturer Part Number: PM6670S
• Description: IC CTLR DDR2/3 MEM PS VFQFPN-24
• Manufacturer: STMicroelectronics

Specifications of PM6670S

• Applications: Memory, DDR2/DDR3 Regulator
• Current - Supply: 800µA
• Voltage - Supply: 4.5 V ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-VFQFN, 24-VFQFPN
• For Use With: 497-8411 - BOARD EVAL PM6670S DDR2/3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Device description
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The duty-cycle of the buck converter is, in steady-state conditions, given by
Equation 2
The switching frequency is thus calculated as
Equation 3
where
Equation 4a
Equation 4b
Referring to the typical application schematic (figures on cover page and
final expression is then:
Equation 5
Even if the switching frequency is theoretically independent from battery and output
voltages, parasitic parameters involved in power path (like MOSFETs' on-resistance and
inductor's DCR) introduce voltage drops responsible for slight dependence on load current.
In addition, the internal delay is due to a small dependence on input voltage. The PM6670S
switching frequency can be set by an external divider connected to the VOSC pin.
Figure 29. Switching frequency selection and VOSC pin
The suggested voltage range for VOSC pin is 0.3 V to 2 V, for better switching frequency
programmability.
f
SW
Doc ID 14432 Rev 4
=
f
SW
R2
R1
T
D
ON
VIN
=
K
α
=
α
OSC
OSC
α
K
OSC
OUT
D
OSC
=
V
=
VOSC
V
OUT
=
=
V
--------------
IN
R
V
V
V
OUT
PM6670S
1
V
-------------- -
--------------
V
OSC
V
SNS
PM6670
IN
R
V
+
OSC
OUT
SNS
2
IN
R
2
=
⋅
α
α
K
OSC
OUT
OSC
1
⋅
K
OSC
1
Figure 29
PM6670S
), the