TMI3253T

General Description

The TMI3253 / TMI3253S / TMI3253T are high-efficiency synchronous step-down DC-DC converters using Constant On-Time (COT) control with a 600 kHz switching frequency.

The devices can deliver up to 3 A of output current and up to 3.5 A at 1.2 V output, under appropriate operating and thermal conditions.

The devices integrate both the main high-side switch and synchronous low-side switch with very low RDS(ON):

• high-side MOSFET: 70 mΩ;
• low-side MOSFET: 35 mΩ.

The low MOSFET resistance minimizes conduction losses and provides high conversion efficiency.

The 600 kHz switching frequency allows the use of smaller external inductors and capacitors while maintaining low output-voltage ripple.

The COT architecture provides fast transient response, making the devices suitable for applications requiring rapid response to load changes.

The devices include integrated internal compensation and are stable with low-ESR ceramic output capacitors.

The TMI3253/S/T requires a minimum number of standard external components and is available in a compact SOT23-6 RoHS-compliant package.

Key Features

• 70 mΩ / 35 mΩ low-RDS(ON) integrated MOSFETs.
• High-efficiency synchronous operation.
• Wide input-voltage range: 4.5 V to 18 V.
• Output voltage:
  • 0.8 V — TMI3253;
  • 0.6 V — TMI3253S;
  • 0.765 V — TMI3253T.
• 600 kHz switching frequency.
• Up to 3 A output current.
• Up to 3.5 A at 1.2 V output.
• COT control for fast transient response.
• Power-Save Mode at light load.
• Integrated internal compensation.
• Stable operation with low-ESR ceramic output capacitors.
• Over-current protection with Hiccup Mode.
• Thermal shutdown.
• Inrush-current limiting.
• Soft-start function.
• Built-in input over-voltage protection.
• Available in SOT23-6 package.

Device Variants

Applications

• Digital Set-Top Boxes.
• Flat-Panel Televisions and Monitors.
• Notebook Computers.
• Wireless Modems.
• DSL Modems.
• Digital equipment power-supply circuits.

Repair-Oriented Notes

The TMI3253/S/T is a synchronous buck converter, meaning both power MOSFETs are integrated into the IC. External circuitry normally consists of the inductor, input/output capacitors, feedback components, and other supporting components.

In a repair situation, if the output voltage is missing, check:

• input voltage at the IC;
• output short circuit or excessive load;
• inductor continuity;
• feedback network;
• signs of overheating or internal MOSFET failure.

If the converter repeatedly starts and stops, the Hiccup over-current protection may be activating because of an overloaded or shorted output.

The specified 35 mΩ and 70 mΩ RDS(ON) values are characteristics of the internal MOSFETs and should not be interpreted as expected resistance measurements between arbitrary IC pins with a multimeter.

Tags: TMI3253, TMI3253S, TMI3253T, Buck converter, DC-DC, 18V, 3A, 600kHz, SOT-23-6, synchronous step-down converter