PM6670AS View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'PM6670AS' PDF : 54 Pages View PDF
Device description
PM6670AS
7.1.5
When the MODE pin is connected to +5 V, the PM6670AS allows setting the VDDQ voltage
to 1.8 V or 1.5 V just forcing the DDRSEL multilevel pin to +5 V or to ground respectively
(see Figure 33a).
In this condition the pulse-skip feature is enabled. This device configuration is suitable for
standard DDR2/3 memory supply applications avoiding the need for an external, high
accuracy, divider for output voltage setting.
Applications requiring different output voltages can be managed by PM6670AS simply
setting the adjustable mode. If MODE pin voltage is higher than 4 V, the fixed output mode is
selected. Connecting an external divider to the MODE pin (Figure 33b), it is used as
negative input of the error amplifier and the output voltage is given by expression (21).
Equation 21
VDDQ ADJ
=
0.9 ⋅
R8 + R9
R8
VDDQ output voltage can be set in the range from 0.9 V to 2.6 V. Adjustable mode
automatically switches DDRSEL pin to become the power saving algorithm selector: if tied
to +5 V, the forced-PWM (fixed frequency) control is performed. If grounded or connected to
VREF pin (1.237 V reference voltage), the pulse-skip or non-audible pulse-skip modes are
respectively selected.
Table 8. Mode-of-operation settings summary
Mode
DDRSEL
VDDQ
VMODE > 4.3 V
VDDRSEL > 4.2 V
1 V < VDDRSEL < 3.5 V
<0.5 V
1.8 V
1.5 V
VMODE < 3.7 V
VDDRSEL > 4.2 V
1V < VDDRSEL < 3.5 V
VDDRSEL < 0.5 V
ADJ
Operating mode
Pulse-Skip
Forced-PWM
Non-Audible Pulse-skip
Pulse-Skip
Current sensing and current limit
The PM6670AS switching controller uses a valley current sensing algorithm to properly
handle the current limit protection and the inductor current zero-crossing information. The
current is sensed during the conduction time of the low-side MOSFET. The current sensing
element is the on-resistance of the low-side switch. The sensing scheme is visible in
Figure 34.
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Doc ID 14436 Rev 2
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