Datasheet LTC3416 (Analog Devices) - 10

LTC3416
U U W U APPLICATIO S I FOR ATIO
coincidentally or ratiometrically track another output volt- selected the same as that of VOUT1’s resistor divider. To age as shown in Figure 3. implement the ratiometric sequencing in Figure 3b, the extra resistor divider’s ratio should be set so that the If the voltage on the TRACK pin is less than 0.8V, voltage TRACK pin voltage exceeds 1.05V by the end of the start- tracking is enabled. During voltage tracking, the output up period. The LTC3416 utilizes a method in which the voltage regulates to the tracking voltage through a resistor TRACK pin’s control over the output voltage is gradually divider network. The output voltage during tracking can be released as the TRACK pin voltage approaches 0.8V. With calculated with the following equation: this technique, some overdrive will be required on the ⎛ R2⎞ TRACK pin to ensure that the tracking function is com- V = V OUT TRACK 1+ ⎝⎜ , V pletely disabled at the end of the start-up period. R ⎠⎟ 1 TRACK < 0.8V For coincident tracking, the following condition should be Voltage tracking can be accomplished by sensing a frac- satisfied to ensure that tracking is disabled at the end of tion of the output voltage from another regulator. This is start-up. typically done by using a resistor divider to attenuate the output voltage that is being tracked. Setting this attenua- VOUT2 ≥ 1.32 VOUT1 tion factor equal to the reciprocal of the gain factor For ratiometric tracking, the following equation can be provided by the feedback resistors will force the regulator used to calculate the resistor values: outputs to be equal to each other during tracking. If tracking is not desired, connect the TRACK pin to SVIN. ⎛ V ⎞ R4 R OUT 3 2 = – 1 To implement the coincident tracking shown in Figure 3a, ⎝⎜ VTRACK ⎠⎟ connect an extra resistor divider to the output of VOUT2 and connect its midpoint to the TRACK pin of the LTC3416 as V ≥1.05V TRACK shown in Figure 4. The ratio of this divider should be VOUT2 VOUT2 VOUT1 VOUT1 OUTPUT VOLTAGE OUTPUT VOLTAGE 3416 F03 TIME TIME
(3a) Coincident Tracking (3b) Ratiometric Sequencing Figure 3. Two Different Modes of Output Voltage Sequencing
VOUT2 R4 R2 TO TO TRACK VFB(MASTER) PIN PIN R3 R1 3416 F04
Figure 4. Setup for Tracking and Ratiometric Sequencing
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