STEVAL-ISA051V1 STMicroelectronics, STEVAL-ISA051V1 Datasheet - Page 21

• Manufacturer Part Number: STEVAL-ISA051V1
• Description: BOARD EVAL PM6670S DDR2/3
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of STEVAL-ISA051V1

• Design Resources: STEVAL-ISA051V1 Gerber Files STEVAL-ISA051V1 Schematic STEVAL-ISA051V1 Bill of Material
• Main Purpose: Special Purpose DC/DC, DDR Memory Supply
• Outputs And Type: 4, Non-Isolated
• Voltage - Output: 1.5V, 1.8V
• Voltage - Input: 4.5 ~ 28V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: PM6670
• Input Voltage: 4.5 V to 28 V
• Output Voltage: 1.8 V, 1.5 V
• Product: Power Management Modules
• Silicon Manufacturer: ST Micro
• Silicon Core Number: PM6670S
• Kit Application Type: Power Management
• Application Sub Type: DDR2/3 Memory Power Supply Controller
• Kit Contents: Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: PM6670S
• Other names: 497-8411

PM6670S
7.1
VDDQ section - constant on-time PWM controller
The PM6670S uses 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’s ESR to trigger
the on-time one-shot generator. In this way, the output capacitor’s 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’s 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. 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
off and a new cycle begins
Figure 28. Inductor current and output voltage in steady state conditions
OSC
is a constant value (130 ns typ.) and τ is the internal propagation delay (40ns
Inductor
Inductor
current
current
Output
Output
voltage
voltage
V
V
reg
reg
(Figure
Ton
Ton
Doc ID 14432 Rev 4
T
28).
ON
=
Toff
Toff
K
OSC
V
V
R
OSC
SNS
= 0.9 V), the synchronous rectifier is turned
+
τ
t
t
Device description
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