LMZ21701SILR

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1. Describe

The LMZ21701SILR nanomodule is an easy-to-use step-down DC/DC solution capable of driving loads up to 1000mA in space-constrained applications. Basic operation requires only one input capacitor, one output capacitor, one soft-start capacitor, and two resistors. The LMZ21701SILR Nano module is an easy-to-use step-down DC/DC solution capable of driving loads up to 1000 mA in space-constrained applications. Basic operation requires only one input capacitor, one output capacitor, one soft-start capacitor, and two resistors. Nano modules are available in an 8-pin DFN package with an integrated inductor. The LMZ21701SILR architecture is based on DCS-Control™ (Direct Control with seamless transition to power saving mode). This architecture combines the fast transient response and stability of a hysteretic converter with the precise DC output regulation of voltage-mode and current mode regulators. The LMZ21701 architecture uses Pulse Width Modulation (PWM) mode for moderate and heavy load requirements, and Power Save Mode (PSM) at light loads for high efficiency. In PWM mode, the switching frequency is controlled over the input voltage range. This value depends on the output voltage setting and is usually reduced at low output voltages to improve efficiency. In a PSM, the switching frequency decreases linearly with the load current. Because the device's architecture supports both modes of operation (PWM and PSM) in a single circuit building block, transitions between modes of operation are seamless with minimal impact on output voltage.

2. Feature

    1. Integrated inductor

    2. Tiny 3.5 mm × 3.5 mm × 1.75 mm package

    3. 35-mm² solution size (single-sided)

    4. -40°C to 125°C junction temperature range

    5. Adjustable output voltage

    6. Comprehensive compensation

    7. Adjustable soft-start function

    8. Start up pre-biased load

    9. Power good and enable pins

  10. Seamless transition to power saving mode

  11. Output current up to 1000 mA

  12. Input voltage range 3 V to 17 V

  13. Output voltage range 0.9 V to 6 V

  14. Efficiency up to 95 %

  15. 1.5µA Shutdown Current

  16. 17µA quiescent current

  17. Create custom designs using LMZ21701 and WEBENCH® Power Designer

3. Application

    1. Point-of-load conversion for 3.3 V, 5 V or 12 V input voltage

    2. Space-constrained applications

    3. LDO replacement

4. Pin configuration

5. Pin Description

6. Function Description

    1. Input undervoltage lockout

        The LMZ21701SILR has an input undervoltage lockout (UVLO) circuit. It monitors the input voltage level and prevents the device from switching the power MOSFET if VIN is not high enough. The typical VIN UVLO rising threshold is 2.9 V with 180 mV hysteresis.

    2. Enable Input (EN)

        The enable pin (EN) is weakly pulled down internally through a 400-kΩ resistor to keep EN logic low when the pin is floating. Pull-down resistors are not connected when EN is set high. Once the voltage on the enable pin (EN) is set high, the Nano module will start to operate. If EN is set low (< 0.3 V), the LMZ21701 will enter shutdown mode. Typical shutdown quiescent current is 1.5 μA.

    3. Soft Start and Tracking (SS)

        When EN is set high for device operation, the LMZ21701SILR starts switching after a 50µs delay and the output voltage begins to rise. The VOUT rising slope is controlled by an external capacitor CSS connected to the soft-start (SS) pin. When EN is pulled low and thermal protection is turned off, the soft-start capacitor voltage is reset to zero volts positive. If tracking is required, the SS pin can be used to track an external voltage.

    4. Power Good (PG)

        The LMZ21701SILR has a power good feature that can be used to sequence multiple power rails. The PG pin is an open-drain output and requires a pull-up resistor RPG to VOUT (or any other external voltage less than 7 V). When the Nano module is enabled and the UVLO is met, the power good function starts monitoring the output voltage. If the output does not reach the proper regulation voltage, the PG pin remains logic low.

    5. Output current limit and output short circuit protection

        The LMZ21701SILR has integrated protection against heavy loads and output short circuit events. Both the high-side FET and the low-side FET have current monitoring circuits. If the current limit threshold of the high-side FET is reached, the high-side FET will turn off and the low-side FET will turn on to reduce the inductor current. Once the current through the low-side FET falls below a safe level, the high-side device is allowed to turn on again. The actual DC output current depends on the input voltage, output voltage and switching frequency.

7. Application Information

The LMZ21701 is a step-down DC-DC converter. It is used to convert a higher DC voltage to a regulated lower DC voltage with a maximum load current of 1 A. The following design process can be used to select components for the LMZ21701. Or, use WEBENCH® software to select from a large component database, run electrical simulations, and optimize designs for specific performance.