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TPS62684 Datasheet(PDF) 14 Page - Texas Instruments
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TPS62684 Datasheet(HTML) 14 Page - Texas Instruments
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SLVSAC5 – APRIL 2014
Feature Description (continued)
< RBW (resolution bandwidth): The receiver is not able to distinguish individual side-band harmonics, so,
several harmonics are added in the input filter and the measured value is higher than expected in theoretical
> RBW: The receiver is able to properly measure each individual side-band harmonic separately, so the
measurements match with the theoretical calculations.
9.4 Device Functional Modes
The TPS62684 device starts operation when EN is set high. For proper operation, the EN pin must be terminated
and must not be left floating. The device should only be enabled when the input voltage is stable and has
ramped above its minimum supply of 3.25V.
Pulling the EN pin low forces the device into shutdown, with a shutdown current of typically 0.2
μA. In this mode,
the internal high side and low side MOSFETs are turned off, the internal resistor feedback divider is
disconnected, and the entire internal-control circuitry is switched off. The TPS62684 device actively discharges
the output capacitor when it turns off. The integrated discharge resistor has a typical resistance of 12
internal discharge transistor is only turned on after the device had been enabled at least once. The required time
to discharge the output capacitor at the output node depends on load current and the effective output
capacitance. The TPS62684 is designed such that it can start into a pre-biased output, in case the output
discharge circuit was active for too short a time to fully discharge the output capacitor. In this case, the converter
starts switching as soon as the internal reference has approximately reached the equivalent voltage to the output
voltage present. It then ramps the output from that voltage level to its target value.
9.4.2 Soft Start
The TPS62684 has an internal soft start circuit that controls the ramp up of the output voltage. Once the
converter is enabled and the input voltage is above the undervoltage lockout threshold V
, the output voltage
ramps up to 95% of its nominal value within t
of typ. 150μs. This ensures a controlled ramp up of the output
voltage and limits the input voltage drop when a battery or a high-impedance power source is connected to the
input of the DC/DC converter.
The inrush current during start-up is directly related to the effective capacitance and load present at the output of
During soft start, the current limit is reduced to 2/3 of its nominal value. Once the internal reference voltage has
reached 90% of its target value, the current limit is set to its nominal target value.
9.4.3 Undervoltage Lockout
The undervoltage lockout circuit prevents the device from misoperation at low input voltages. It prevents the
converter from turning on either MOSFET under undefined conditions. The TPS62684 has a rising UVLO
threshold of 2.1V (typical).
9.4.4 Short-Circuit Protection
The TPS62684 integrates current limit circuitry to protect the device against heavy load or short circuits. When
the average current in the high side MOSFET reaches its current limit, the high side MOSFET is turned off and
the low side MOSFET is turned on ramping down the inductor current.
As soon as the converter detects a short circuit condition it shuts down. After a delay of approximately 20 µs, the
converter restarts. In case the short circuit condition remains, the converter shuts down again after hitting the
current limit threshold. In case the short circuit condition remains present on the converters output, the converter
periodically re-starts with a small duty cycle as the output voltage is zero and shuts down again, thereby limiting
the current drawn from the input.
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