LMZ23603TZ/NOPB

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1. Description

The LMZ23603TZ/NOPB SIMPLE SWITCHER®power module is an easy-to-use step-down DC-DC solution capable of driving up to 3-A load. The LMZ23603 is available in an innovative package that enhances thermal performance and allows for hand or machine soldering. The LMZ23603 can accept an input voltage rail between 6 V and 36 V and deliver an adjustable and highly accurate output voltage as low as 0.8 V. The LMZ23603 only requires two external resistors and three external capacitors to complete the power solution. The LMZ23603 is a reliable and robust design with the following protection features: thermal shutdown, programmable input undervoltage lockout, output overvoltage protection, short circuit protection, output current limit, and allows start-up into a prebiased output. The sync input allows synchronization over the 650-kHz to 950-kHz switching frequency range.

2. Features

    1. Integrated Shielded Inductor

    2. Simple PCB Layout

    3. Frequency Synchronization Input (650 kHz to 950 kHz)

    4 . Flexible Startup Sequencing Using External Soft- start, Tracking and Precision Enable

    5. Protection Against Inrush Currents and Faults Such as Input UVLO and Output Short Circuit

    6. Junction Temperature Range –40°C to 125°C 

    7. Single Exposed Pad and Standard Pinout for Easy Mounting and Manufacturing

    8. Fast Transient Response for Powering FPGAs and ASICs

    9. Fully Enabled for WEBENCH® Power Designer

  10. Pin Compatible With LMZ22005/LMZ23605/LMZ22003

  11. Performance Benefits

        – High Efficiency Reduces System Heat Generation

        – Low component count, only 5 external components

        – Low output voltage ripple

        – Uses PCB as heat sink, no airflow required

  12. Electrical Specifications

        – 18-W maximum total output power

        – Up to 3-A output current

       – Input voltage range 6 V to 36 V

       – Output voltage range 0.8 V to 6 V

       – Efficiency up to 92%

3. Pin Configuration 

5. Pin Functions

6. Switch Output

This is the output of a power MOSFET switch connected directly to the input voltage. The switch provides energy to an inductor, an output capacitor and the load circuitry under control of an internal pulse-width-modulator (PWM). The PWM controller is internally clocked by a fixed 260-kHz oscillator. In a standard step-down application the duty cycle (Time ON/Time OFF) of the power switch is proportional to the ratio of the power supply output voltage to the input voltage. The voltage on pin 1 switches between VIN (switch ON) and below ground by the voltage drop of the external Schottky diode (switch OFF).

7. Input

The input voltage for the power supply is connected to pin 2. In addition to providing energy to the load the input voltage also provides bias for the internal circuitry of the LM2673. For ensured performance the input voltage must be in the range of 8 V to 40 V. For best performance of the power supply the input pin must always be bypassed with an input capacitor located close to pin 2.

8. C Boost

A capacitor must be connected from pin 3 to the switch output, pin 1. This capacitor boosts the gate drive to the internal MOSFET above VIN to fully turn it ON. This minimizes conduction losses in the power switch to maintain high efficiency. The recommended value for C Boost is 0.01 µF.

9. Ground

This is the ground reference connection for all components in the power supply. In fast-switching, high-current applications such as those implemented with the LM2673, TI recommends that a broad ground plane be used to minimize signal coupling throughout the circuit.

10. Current Adjust

A key feature of the LM2673 is the ability to tailor the peak switch current limit to a level required by a particular application. This alleviates the need to use external components that must be physically sized to accommodate current levels (under shorted output conditions for example) that may be much higher than the normal circuit operating current requirements. A resistor connected from pin 5 to ground establishes a current (I(pin 5) = 1.2 V / RADJ) that sets the peak current through the power switch. The maximum switch current is fixed at a level of 37,125 / RADJ.

11. Feedback

This is the input to a two-stage high gain amplifier, which drives the PWM controller. It is necessary to connect pin 6 to the actual output of the power supply to set the DC output voltage. For the fixed output devices (3.3-V, 5- V, and 12-V outputs), a direct wire connection to the output is all that is required as internal gain setting resistors are provided inside the LM2673. For the adjustable output version two external resistors are required to set the dc output voltage. For stable operation of the power supply it is important to prevent coupling of any inductor flux to the feedback input