STEVAL-ISA052V2 STMicroelectronics, STEVAL-ISA052V2 Datasheet - Page 16

• 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
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Device description
The PM6675AS combines a single high efficiency step-down controller and an independent
Low Drop-Out (LDO) linear regulator in the same package.
The switching controller section is a high-performance, pseudo-fixed frequency, Constant-
On-Time (COT) based regulator specifically designed for handling fast load transient over a
wide range of input voltage.
The switching section output can be easily set to a fixed 1.5 V voltage without additional
components or adjusted in the 0.6 V to 3.3 V range using an external resistor divider. The
Switching Mode Power Supply (SMPS) can handle different modes of operation in order to
minimize noise or power consumption, depending on the application needs. Selectable low-
consumption and low-noise modes allow the highest efficiency and a 33 kHz minimum
switching frequency respectively at light loads.
The current sensing is lossless, based on the Low-Side MOSFET turn-on resistance.
The input of the LDO can be either the switching section output or a lower voltage rail in
order to reduce the total power dissipation. Linear regulator stability is achieved by filtering
its output with a ceramic capacitor (20 µF or greater). The LDO linear regulator can sink and
source up to 2 Apk.
Two fixed current limit (±1A-±2A) can be chosen.
An active soft-end is independently performed on both the switching and the linear
regulators outputs when disabled.
Switching section - constant on-time pwm controller
The PM6675AS employes a pseudo-fixed frequency, Constant On-Time (COT) controller as
the core of the switching section. As well known, the COT controller concerns of 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,
sensed at VSNS pin, and inversely proportional to the input voltage, sensed at the VOSC
pin, as follows:
Equation 1
where K
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.
OSC
is a constant value (130 ns typ.) and τ is the internal propagation delay (40ns
T
ON
=
K
OSC
V
V
OSC
SNS
+
τ
PM6675AS