STEVAL-ISA051V1 STMicroelectronics, STEVAL-ISA051V1 Datasheet - Page 32

• Manufacturer Part Number: STEVAL-ISA051V1
• Description: BOARD EVAL PM6670S DDR2/3
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of STEVAL-ISA051V1

• Design Resources: STEVAL-ISA051V1 Gerber Files STEVAL-ISA051V1 Schematic STEVAL-ISA051V1 Bill of Material
• Main Purpose: Special Purpose DC/DC, DDR Memory Supply
• Outputs And Type: 4, Non-Isolated
• Voltage - Output: 1.5V, 1.8V
• Voltage - Input: 4.5 ~ 28V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: PM6670
• Input Voltage: 4.5 V to 28 V
• Output Voltage: 1.8 V, 1.5 V
• Product: Power Management Modules
• Silicon Manufacturer: ST Micro
• Silicon Core Number: PM6670S
• Kit Application Type: Power Management
• Application Sub Type: DDR2/3 Memory Power Supply Controller
• Kit Contents: Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: PM6670S
• Other names: 497-8411

Device description
7.1.6
32/54
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 PM6670S 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
110 mV fixed threshold.
POR, UVLO and soft-start
The PM6670S 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 (4.25 V typ.), keeping active the internal
discharge MOSFETs (only if AVCC > 1 V).
The soft-start allows a gradual increase of the internal current limit threshold during start-up
reducing the input/output surge currents. At the beginning of start-up, the PM6670S current
limit is set to 25 % of nominal value and the under voltage protection is disabled. Then, the
current limit threshold is sequentially brought to 100 % in four steps of approximately 750 μs
(
Figure 37. Soft-start waveforms
Figure 37
).
Figure 36
Switching output
, the R
ILIM
setting resistor design.
Current limit threshold
S5
DS(on)
Doc ID 14432 Rev 4
ILIM
sensing technique allows high efficiency performance
I
CL
must be calculated to set a limit threshold given by the
=
120
μ
A
⋅
R
R
DSon
ILIM
Time
PM6670S
rd