LMZ14203H IC

Technical Specifications of LMZ14203HEVAL/NOPB

Datasheet	LMZ14203HEVAL/NOPB datasheet
Category	Programmers, Development Systems
Family	Evaluation Boards – DC/DC & AC/DC (Off-Line) SMPS
Manufacturer	Texas Instruments
Series	SIMPLE SWITCHER?
Part Status	Active
Main Purpose	DC/DC, Step Down
Outputs and Type	1, Non-Isolated
Power – Output	–
Voltage – Output	12V
Current – Output	3A
Voltage – Input	15 V ~ 42 V
Regulator Topology	Buck
Frequency – Switching	Up to 1MHz
Board Type	Fully Populated
Supplied Contents	Board
Utilized IC / Part	LMZ14203H

LMZ14203H Description

The LMZ14203H SIMPLE SWITCHER® power module is a high-performance, low-cost step-down DC-DC solution with excellent power conversion efficiency, line and load regulation, and output accuracy. It can drive loads of up to 3 A. With its cutting-edge package, the LMZ14203H improves thermal performance and may be soldered by hand or machine.

The LMZ14203H takes in a rail voltage input of 6 V to 42 V and outputs a voltage as low as 5 V with a wide range of adjustability and good accuracy. To finish the power solution, the LMZ14203H only needs three more external resistors and four more capacitors. The protection features included in the LMZ14203H make it a dependable and sturdy piece of equipment: thermal shutdown, input under-voltage lockout, short-circuit protection, output overvoltage protection, output current limit, and the ability to start up into a pre-biased output. The switching frequency can be modified by a single resistor up to 1 MHz.

Features for the LMZ14203H

• Integrated Shielded Inductor
• Simple PCB Layout
• Flexible Startup Sequencing Using External Soft-
  Start and Precision Enable
• Protection Against Inrush Currents
• Input UVLO and Output Short-Circuit Protection
• –40°C to 125°C Junction Temperature Range
• Single Exposed Pad and Standard Pinout for Easy
  Mounting and Manufacturing
• Low Output Voltage Ripple

Detailed Description

● COT Control Circuit Overview

The output voltage is fed back and compared to an internal 0.8-V reference, allowing precise control of the ON time using a comparator and a one-shot. For a predetermined time, as programmed by a resistor RON, the high-side MOSFET will be active if the feedback voltage is less than the reference. The relationship between RON and VIN limits the time the device is “ON” as the input voltage increases. After this period of ON-time, the high-side MOSFET is disabled for at least 260 ns. The ON-time cycle is reset if the voltage at the feedback pin drops below the setpoint again. This is how regulation is accomplished.

Feature Description

Indicator of Excess Voltage at the Output The FB voltage is compared to an in-built standard of 0.92 V. Once FB goes beyond 0.92 V, and the ON time is cut off instantly. Overvoltage protection is the term used for this situation (OVP). Extreme changes in the input voltage or the output load might cause this. The maximum ON times of the MOSFETs will be reduced once OVP is engaged. As a bonus, the synchronous MOSFET will stay on until the current in the inductor is zero.

● Current Limit

When the power is not being used, the synchronous MOSFET’s current is monitored to detect the current limit. When the top MOSFET is disabled, the inductor current travels through the load, the PGND pin, and the internal synchronous MOSFET, as shown in the Functional Block Diagram.

The current limit comparator prevents the beginning of the next ON time from occurring if the current exceeds 4.2 A (typical). If the FB input is less than 0.8 V and the inductor current is less than 4.2 A, the next switching cycle will occur. The current via the inductor is measured whenever the synchronous MOSFET is on. If the current through the inductor is more than 4.2 A, the top MOSFET will not switch on for additional ON periods. Because of the prolonged OFF-time, switching occurs at a lower frequency when the current is limited.

● Thermal Protection

The LMZ14203H’s junction temperature must never go above its safe operating range. To prevent damage from overheating, the device enters a low-power standby mode when it reaches a temperature of 165 degrees Celsius (typical). The primary MOSFET is still turned off, lowering VO, and the CSS capacitor is discharged to the ground, further reducing VO. Devices should have thermal protection to avoid catastrophic failure due to accidental overheating. Normal operation is resumed when the junction temperature drops below 145 °C (typical Hyst = 20 °C), at which point the SS pin is freed, and VO begins to climb smoothly.

● Zero Coil Current Detection

The zero coil current detecting circuit keeps tabs on the current flowing through the lower (synchronous) MOSFET and disables it until the next ON-time. This circuit allows it to operate in the more efficient DCM mode when few demands are placed on the system.

● Prebiased Startup

The LMZ14203H will enter a correct pre-biased output startup state. The existence of current channels across power rails during startup is a common occurrence in multiple rail logic applications. When calculating the output voltage, the prebias level must be less than the UVLO reference voltage. As a result, the regulator’s output pre-bias won’t be able to turn on the high-side MOSFET body diode and turn on the regulator.

● Device Functional Modes

Modes of Discontinuous and Continuous Conduction The regulator enters a state of discontinuous conduction when the load is low (DCM). When the load current is higher than the critical conduction point, it will function in continuous conduction mode (CCM). In DCM operation, the inductor current begins at zero amps, rises to a peak, then falls back to zero before the end of the OFF period.

When the current through the inductor is at zero, the load is powered solely by the output capacitor. The next ON time period begins when the FB pin voltage drops below the internal reference. With DCM, the switching frequency is lower and more variable with load current than with CCM. DCM maintains its conversion efficiency even when the load is reduced, and the switching frequency is lowered because these changes reduce the conduction and switching losses.

Conclusion

An input voltage of 4.5 V to 42 V is acceptable for the operation of the LMZ14203H device. This input supply needs to be well regulated, handle maximum input current, and have a consistent voltage during its operation. For the LMZ14203H not to produce a false UVLO fault and reset the system, the input supply rail resistance must be low enough to prevent a significant voltage drop. The bulk capacitance may be needed in addition to the ceramic bypass capacitors if the input supply is further away from the LMZ14203H than a few inches. It doesn’t matter if the capacitor has 47 F or 100 F of bulk capacitance; these values are standard for electrolytic capacitors.

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