TPS62660YFFT Integrated Circuits (ICs)

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1. Describe

The TPS62660YFFT device is a high frequency synchronous step-down DC-DC converter optimized for battery powered portable applications. Designed for low-power applications, the TPS62660YFFT supports peak load currents up to 1000mA and allows the use of low-cost chip inductors and capacitors. The device features a wide input voltage range of 2.3 V to 5.5 V, supporting applications powered by Li-Ion batteries with an extended voltage range. Different fixed voltage output versions are available from 1.2V to 2.3V. The TPS62660YFFT operates at a regulated 6MHz switching frequency and enters a power-saving mode at light load currents to maintain high efficiency over the entire load current range. PFM mode extends battery life by reducing quiescent current to 31 μA (typ) during light loads and standby operation. For noise sensitive applications, the device can be forced into fixed frequency PWM mode by pulling the MODE pin high. In shutdown mode, current consumption drops below 1 μA. The TPS6266x is available in a 6-pin chip scale package (DSBGA).

2. Feature

    1. 91% efficiency at 6MHz operation

    2. 31μA quiescent current

    3. Wide VIN range of 2.3 V to 5.5 V

    4. 6MHz regulated frequency operation

    5. Best-in-class load and line transients

    6. ±2% total DC voltage accuracy

    7. Automatic PFM or PWM mode switching

    8. Low ripple light load PFM mode

    9. Fast turn-on time: < 60-µs turn-on time

  10. Integrated active power-down sequencing (optional)

  11. Current overload and thermal shutdown protection

  12. Requires three surface mount external components (one MLCC inductor, two ceramic capacitors)

  13. Complete sub-1mm component profile solution

  14. Overall solution size <12 mm2

  15. Available in 6-pin NanoFree™ (DSBGA)

3. Application

    1. Cell phones and smartphones

    2. PDAs and Palmtops

    3. Portable hard drive

    4. DC-DC Micro Modules

4. Pin configuration

5. Pin Description

6. Feature Description

    1. Switching Frequency

        The magnitude of the internal ramp, which is generated from the duty cycle, reduces for duty cycles either set of 50%. Thus, there is less overdrive on the main comparator inputs which tends to slow the conversion down. The intrinsic maximum operating frequency of the converter is about 10 MHz to 12 MHz, which is controlled to approximately 6 MHz by a frequency-locked loop. When high or low duty cycles are encountered, the loop runs out of range and the conversion frequency falls below 6 MHz. The tendency is for the converter to operate more towards a constant inductor peak current rather than a constant frequency. In addition to this behavior which is observed at high duty cycles, it is also noted at low duty cycles. When the converter is required to operate towards the 6-MHz nominal at extreme duty cycles, the application can be assisted by decreasing the ratio of inductance (L) to the output capacitor's equivalent serial inductance (ESL). This increases the ESL step seen at the main comparator's feedback input, thus decreasing its propagation delay, hence increasing the switching frequency.

    2. Mode Selection

        The MODE pin allows to select the operating mode of the device. Connecting this pin to GND enables the automatic PWM and power-save mode operation. The converter operates in regulated frequency PWM mode at moderate to heavy loads and in the PFM mode during light loads, which maintains high efficiency over a wideload current range. Pulling the MODE pin high forces the converter to operate in the PWM mode even at light load currents. The advantage is that the converter operates with a fixed frequency that allows simple filtering of the switching frequency for noise-sensitive applications. In this mode, the efficiency is lower compared to the power-save mode during light loads. For additional flexibility, it is possible to switch from power-save mode to forced PWM mode during operation. This allows efficient power management by adjusting the operation of the converter to the specific system requirements.

    3. Soft Start

        The TPS62660YFFT has an internal soft-start circuit that limits the inrush current during start-up. This limits input voltage drops when a battery or a high-impedance power source is connected to the input of the converter. The soft-start system progressively increases the ON-time from a minimum pulse-width of 35 ns as a function of the output voltage. This mode of operation continues for approximately 100 μs after enable. Should the output voltage not have reached its target value by this time, such as in the case of heavy load, the soft-n operates in a current limit mode, specifically the P-MOS current limit is set to half the nominal limit, and the N- channel MOSFET remains on until the inductor current has reset. After a further 100 μs, the device ramps up to the full current limit operation if the output voltage has risen above 0.5 V (approximately). Therefore, the start-up time mainly depends on the output capacitor and load current. The TPS62661 device starts up immediately into a nominal current limit mode, thereby ramping up the output voltage with maximum speed (<60 μs typically). The start-up time mainly depends on the output capacitor and load current.

    4. Output Capacitor Discharge

        The TPS62660YFFT device can actively discharge the output capacitor when it turns off. The integrated discharge resistor has a typical resistance of 15 Ω. The required time to discharge the output capacitor at the output node depends on load current and the output capacitance value.

    5. Undervoltage Lockout

        The undervoltage lockout circuit prevents the device from misoperation at low input voltages. It prevents the converter from turning on the switch or rectifier MOSFET under undefined conditions. The TPS6266x device have a UVLO threshold set to 2.05 V (typical). Fully functional operation is permitted down to 2.1-V input voltage.

    6. Short-Circuit Protection

        The TPS62660YFFT integrates a P-channel MOSFET current limit to protect the device against heavy load or short circuits. When the current in the P-channel MOSFET reaches its current limit, the P-channel MOSFET is turned off and the N-channel MOSFET is turned on. The regulator continues to limit the current on a cycle-by-cycle basis. As soon as the output voltage falls below approximately 0.4 V, the converter current limit is reduced to half of the nominal value. Because the short-circuit protection is enabled during start-up, the device does not deliver more than half of its nominal current limit until the output voltage exceeds approximately 0.5 V. Consider this when a load acting as a current sink is connected to the output of the converter.