PM6670AS STMicroelectronics, PM6670AS Datasheet - Page 31

• 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

PM6670AS
7.1.6
Figure 34. Current sensing scheme
An internal 120 μA current source is connected to C
input of the positive current limit comparator. When the voltage drop developed across the
sensing parameter equals the voltage drop across the programming resistor R
controller skips subsequent cycles until the overcurrent condition is detected or the output
UV protection latches off the device (see
protections on page 35
Referring to
without the need for an external sensing resistor. The on-resistance of the MOSFET is
affected by temperature drift and nominal value spread of the parameter itself; this must be
considered during the R
It must be taken into account that the current limit circuit actually regulates the inductor
valley current. This means that R
maximum DC output current plus half of the inductor ripple current:
Equation 22
The PM6670AS provides also a fixed negative current limit to prevent excessive reverse
inductor current when the switching section sinks current from the load in forced-PWM (3
quadrant working conditions). This negative current limit threshold is measured between
PHASE and PGND pins, comparing the drop magnitude on PHASE pin with an internal
120 mV fixed threshold.
POR, UVLO and soft-start
The PM6670AS automatically performs an internal startup sequence during the rising
phase of the analog supply of the device (AVCC). The switching controller remains in a
stand-by state until AVCC crosses the upper UVLO threshold (4.2 V typ.), keeping active the
internal discharge MOSFETs (only if AVCC > 1 V).
Figure 34
, the RDSon sensing technique allows high efficiency performance
PM6670AS
).
ILIM
PM6670
PM6670
PGND
PGND
setting resistor design.
Doc ID 14436 Rev 2
HGATE
HGATE
PHASE
PHASE
LGATE
LGATE
CSNS
CSNS
ILIM
I
CL
must be calculated to set a limit threshold given by the
100µA·
100µA·
=
Section 7.1.11: Over voltage and under voltage
120
R
R
ILIM
ILIM
μ
A
V
V
⋅
R
IN
IN
R
DSon
I
I
ILIM
VALLEY
VALLEY
SNS
·
·
R
R
pin that is also the non-inverting
DSon
DSon
V
V
OUT
OUT
Device description
ILIM
, the
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