STEVAL-ISA052V1 STMicroelectronics, STEVAL-ISA052V1 Datasheet - Page 28

• 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
7.1.3
28/53
Pulse-skip and no-audible pulse-skip modes
High efficiency at light load conditions is achieved by PM6675S by entering the Pulse-Skip
Mode (if enabled). At light load conditions the zero-crossing comparator truncates the low-
side switch On-Time as soon as the inductor current becomes negative; in this way the
comparator determines the On-Time duration instead of the output ripple.
(see
Figure 37. Inductor current and output voltage at light load with Pulse-Skip
As a consequence, the output capacitor is left floating and its discharge depends solely on
the current drained from the load. When the output ripple on the pin COMP falls under the
reference, a new shot is triggered and the next cycle begins. The Pulse-Skip mode is
naturally obtained enabling the zero-crossing comparator and automatically takes part in the
COT algorithm when the inductor current is about half the ripple current amount, i.e.
migrating from continuous conduction mode (C.C.M.) to discontinuous conduction mode
(D.C.M.).
The output current threshold related to the transition between PWM Mode and Pulse-Skip
Mode can be approximately calculated as:
Equation 19
At higher loads, the inductor current never crosses the zero and the device works in pure
PWM mode with a switching frequency around the nominal value.
A physiological consequence of Pulse-Skip Mode is a more noisy and asynchronous (than
normal conditions) output, mainly due to very low load. If the Pulse-Skip is not compatible
with the application, the PM6675S allows the user to choose between forced-PWM and No-
Audible Pulse-Skip alternative modes (see
page 30
Figure 37
Inductor
current
Output
voltage
V
for details).
reg
).
T
ON
T
OFF
I
LOAD
(
PWM
2
Skip
T
IDLE
Section 7.1.4: Mode-of-operation selection on
)
=
V
IN
2
−
⋅
V
L
OUT
⋅
T
ON
PM6675S
t