ADPL74101 datasheet(20/49 Pages) AD

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Data Sheet

ADPL74101

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Startup and Shutdown (RUN and TRACK/SS Pins)

Use the RUN pin to shut down the ADPL74101. Pulling the RUN pin below 1.08V shuts down the main control loop.

Pulling the RUN pin below 0.7V disables the controller and most internal circuits, including the INTVCC LDO regulators.

In this shutdown state, the ADPL74101 draws only 1μA of quiescent current.

The RUN pin needs to be externally pulled up or driven directly by logic. The RUN pin can tolerate up to 100V (absolute

maximum). Therefore, the pin can be tied to VIN in always-on applications where the controller is enabled

continuously and never shuts down. Additionally, a resistive divider from VIN to the RUN pin can be used to set a

precise input undervoltage lockout so that the power supply does not operate below a user-adjustable level.

The startup of VOUT is controlled by the voltage on the TRACK/SS pin. When the voltage on the TRACK/SS pin is less

than 0.8V internal reference voltage, the ADPL74101 regulates the VFB voltage to the TRACK/SS pin voltage instead of

the 0.8V reference voltage. This method allows the TRACK/SS pin to be used as a soft-start, which smoothly ramps

the output voltage on startup, limiting the input supply inrush current. An external capacitor from the TRACK/SS pin

to GND is charged by an internal 12μA pull-up current, creating a voltage ramp on the TRACK/SS pin. As the TRACK/SS

voltage rises linearly from 0V to 0.8V (and beyond), VOUT rises smoothly from 0V to its final value.

Alternatively, the TRACK/SS pin can be used to make the startup of VOUT track that of another supply. Typically, this

requires connecting to the TRACK/SS pin through an external resistor divider from the other supply to GND. See the

RUN Pin and Undervoltage Lockout section and Soft-Start and Tracking (TRACK/SS Pin) section for more details.

Light Load Operation: Burst Mode Operation, Pulse-Skipping, or Forced

Continuous Mode (MODE Pin)

The ADPL74101 can be set to enter high-efficiency Burst Mode operation, constant-frequency pulse-skipping mode,

or forced continuous conduction mode at light-load currents.

To select Burst Mode operation, tie the MODE pin to GND. To select forced continuous operation, tie the MODE pin to

INTVCC. To select pulse-skipping mode, tie the MODE pin to a DC voltage greater than 1.2V and less than INTVCC – 1.3V.

An internal 100kΩ resistor to GND invokes Burst Mode operation when the MODE pin is floating, and pulse-skipping

mode when the MODE pin is tied to INTVCC through an external 100kΩ resistor.

When the controller is enabled for Burst Mode operation, the minimum peak current in the inductor is set to

approximately 25% of its maximum value, even though the voltage on the ITH pin may indicate a lower value. If the

average inductor current is higher than the load current, the EA decreases the voltage on the ITH pin. When the ITH

voltage drops below 0.425V, the internal sleep signal goes high (enabling sleep mode), and both external FETs turn

off. The ITH pin is then disconnected from the EA output, and parked at 0.45V.

In sleep mode, much of the internal circuitry turns off, reducing the quiescent current drawn by the ADPL74101 to

15µA. When VOUT is 3.2V or higher, the majority of this quiescent current is supplied by the SENSE– pin, which further

reduces the input-referred quiescent current by the ratio of VIN/VOUT multiplied by the efficiency.

In sleep mode, the load current is supplied by the output capacitor. As the output voltage decreases, EA’s output

rises. When the output voltage drops enough, the ITH pin is reconnected to the EA output, the sleep signal goes low,

and the controller resumes normal operation by turning on the top FET on the next cycle of the internal oscillator.

When the controller is enabled for Burst Mode operation, the inductor current is not allowed to reverse. The IR turns

off the bottom FET just before the inductor current reaches zero, preventing it from reversing and going negative.

Therefore, the controller operates in discontinuous operation.

ADPL74101 Datasheet(PDF) 20 Page - Analog Devices

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