ADPL74101 datasheet(32/49 Pages) AD

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Data Sheet

ADPL74101

analog.com

Rev. 0

32 of 49

The VIN UVLO thresholds can be computed by Equation 17 and Equation 18, as follows:

UVLO RISING = 1.2V(1 +

)

(17)

UVLO FALLING = 1.08V(1 +

)

(18)

The current that flows through the R1 and R2 divider adds to the shutdown, sleep, and active current of the

ADPL74101. Ensure to minimize the impact of this current on the overall efficiency of the application circuit. Resistor

values in the MΩ range can be required to keep the impact on quiescent shutdown and sleep currents low.

Soft-Start and Tracking (TRACK/SS Pin)

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 the internal 0.8 V reference, the ADPL74101 regulates the VFB pin voltage to the voltage on the TRACK/SS pin

instead of the internal reference. The TRACK/SS pin can be used to program an external soft-start function or to allow

VOUT to track another supply during startup.

Soft start is enabled by connecting a capacitor from the TRACK/SS pin to GND. An internal 12μA current source

charges the capacitor, providing a linear ramping voltage at the TRACK/SS pin. The ADPL74101 regulates its feedback

voltage (and therefore VOUT) based on the voltage on the TRACK/SS pin, allowing VOUT to rise smoothly from 0V to its

final regulated value. For a desired soft start time (tSS), select a soft start capacitor (CSS) = tSS × 15nF/ms.

Alternatively, the TRACK/SS pin can be used to track another supply during startup, as shown qualitatively in Figure

37 and Figure 38. To track another supply, connect a resistor divider from the leader supply (VX) to the TRACK/SS pin

of the follower supply (VOUT), as shown in Figure 39. During startup, VOUT tracks VX, according to the ratio set by the

resistor divider in Equation 19:

VOUT

RTRACKA

RTRACKA+RTRACKB

RA+RB

(19)

Set RTRACKA = RA and RTRACKB = RB for coincident tracking (VOUT = VX during startup).

Figure 37. Coincident Tracking

Figure 38. Ratiometric Tracking

VX(LEADER)

VOUT(FOLLOWER)

TIME

VX(LEADER)

VOUT(FOLLOWER)

TIME

ADPL74101 Datasheet(PDF) 32 Page - Analog Devices

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