STEVAL-ISA052V1 STMicroelectronics, STEVAL-ISA052V1 Datasheet - Page 20

• 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
20/53
Switching section - constant on-time PWM controller
The PM6675S employes a pseudo-fixed frequency, Constant On-Time (COT) controller as
the core of the switching section. It is well known that the COT controller uses a relatively
simple algorithm and uses the ripple voltage derived across the output capacitor ESR to
trigger the On-Time one-shot generator. In this way, the output capacitor ESR acts as a
current sense resistor providing the appropriate ramp signal to the PWM comparator.
Nearly constant switching frequency is achieved by the system loop in steady-state
operating conditions by varying the On-Time duration, avoiding thus the need for a clock
generator. The On-Time one shot duration is directly proportional to the output voltage,
detected by theVSNS pin, and inversely proportional to the input voltage, detected by the
the VOSC pin, as follows:
Equation 1
where K
(40ns typ.). The one-shot generator directly drives the high-side MOSFET at the beginning
of each switching cycle allowing the inductor current to increase; after the On-Time has
expired, an Off-Time phase, in which the low-side MOSFET is turned on, follows. The Off-
Time duration is solely determined by the output voltage: when lower than the set value (i.e.
the voltage at VSNS pin is lower than the internal reference V
rectifier is turned off and a new cycle begins
Figure 32. Inductor current and output voltage in steady state conditions
OSC
is a constant value (130 ns typ.) and τ is the internal propagation delay
Inductor
current
Output
voltage
V
reg
Ton
T
ON
Toff
=
K
OSC
(Figure
V
V
OSC
SNS
+
32).
τ
R
= 0.6 V), the synchronous
t
PM6675S