STEVAL-ISA052V2 STMicroelectronics, STEVAL-ISA052V2 Datasheet - Page 18

• Manufacturer Part Number: STEVAL-ISA052V2
• Description: BOARD EVAL BASED ON PM6675A
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of STEVAL-ISA052V2

• Design Resources: STEVAL-ISA052V2 Gerber Files STEVAL-ISA052V2 Schematic STEVAL-ISA052V2 Bill of Material
• Main Purpose: DC/DC, Step Down with LDO
• Outputs And Type: 2, Non-Isolated
• Voltage - Output: 1.5V, 0.6 ~ 3.3V
• Voltage - Input: 4.5 ~ 36 V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: PM6675AS
• Input Voltage: 4.5 V to 36 V
• Output Voltage: 1.5 V
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Supplier Unconfirmed
• For Use With/related Products: PM6675AS
• Other names: 497-8413

Device description
7.1.1
18/48
Referring to the typical application schematic (fig. 1 and 23), the final expression is then:
Figure 23. Switching frequency selection and VOSC pin
Equation 5
Even if the switching frequency is theoretically independent from input and output voltages,
parasitic parameters involved in power path (like MOSFET on-resistance and inductor DCR)
introduce voltage drops responsible of a slight dependence on load current.
In addition, the internal delay is cause of a light dependence from input voltage.
The PM6675AS switching frequency can be set by an external divider connected to the
VOSC pin.
The voltage seen at this pin must be greater than 0.8 V and lower than 2 V in order to
ensure system's linearity.
Constant-on-time architecture
Figure 24
The switching regulator of the PM6675AS owns a one-shot generator that turns on the high-
side MOSFET when the following conditions are simultaneously satisfied: the PWM
comparator is high (i.e. output voltage is lower than Vr = 0.6 V), the synchronous rectifier
current is below the current limit threshold and the minimum off-time has expired.
A minimum off-time constrain (300 ns typ.) is introduced to assure the boot capacitor charge
and allow inductor valley current sensing on low-side MOSFET. A minimum On-Time is also
introduced to assure the start-up switching sequence.
Once the on-time has timed out, the high side switch is turned off, while the synchronous
rectifier is ignited according to the anti-cross conduction management circuitry.
When the output voltage reaches the valley limit (determined by internal reference
Vr=0.6 V), the low-side MOSFET is turned off according to the anti-cross conduction logic
once again, and a new cycle begins.
shows the simplified block diagram of the Constant-On-Time controller.
R2
R1
VIN
f
SW
=
K
α
OSC
OSC
VOSC
=
PM6675AS
R
1
R
+
2
R
2
⋅
K
OSC
1
PM6675AS