STEVAL-ISA052V1 STMicroelectronics, STEVAL-ISA052V1 Datasheet - Page 32

• Manufacturer Part Number: STEVAL-ISA052V1
• Description: KIT EVAL PM6675S HE CTLR 2A REG
• Manufacturer: STMicroelectronics

Specifications of STEVAL-ISA052V1

• Main Purpose: DC/DC, Step Down with LDO
• Outputs And Type: 2, Non-Isolated
• Voltage - Output: 1.5V, 0.6 ~ 3.3V
• Current - Output: 10A, 2A
• Voltage - Input: 4.5 ~ 28 V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: PM6675
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-8426

Device description
7.1.6
32/53
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 21
The PM6675S 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 PM6675S 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 > 1V).
The soft-start allows a gradual increase of the internal current limit threshold during startup
reducing the input/output surge currents. At the beginning of start-up, the PM6675S 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 41. Soft-start waveforms
After a fixed 3ms total time, the soft-start finishes and UVP is released: if the output voltage
doesn't reach the under voltage threshold within soft-start duration, the UVP condition is
detected and the device performs a soft-end and latches off. Depending on the load
conditions, the inductor current may or may not reach the nominal value of the current limit
during the soft-start (
Figure 41
).
Switching output
Figure 42
Current limit threshold
SWEN
shows two examples).
ILIM
I
CL
must be calculated to set a limit threshold given by the
=
100
µ
A
⋅
R
R
DSon
ILIM
Time
PM6675S
rd