Datasheet LTC3834 (Analog Devices) - 16
| Manufacturer | Analog Devices |
| Description | 30μA IQ Synchronous Step-Down Controller |
| Pages / Page | 30 / 16 — APPLICATIONS INFORMATION Tracking and Soft-Start (TRACK/SS Pin). Figure … |
| File Format / Size | PDF / 793 Kb |
| Document Language | English |
APPLICATIONS INFORMATION Tracking and Soft-Start (TRACK/SS Pin). Figure 3. Using the TRACK/SS Pin to Program Soft-Start
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LTC3834
APPLICATIONS INFORMATION Tracking and Soft-Start (TRACK/SS Pin)
according to the voltage on the TRACK/SS pin, allowing V The start-up of V OUT to rise smoothly from 0V to its final regulated value. OUT is controlled by the voltage on the The total soft-start time will be approximately: TRACK/SS pin. When the voltage on the TRACK/SS pin is less than the internal 0.8V reference, the LTC3834 reg- 0.8V t = C • ulates the VFB pin voltage to the voltage on the TRACK/ SS SS 1µA SS pin instead of 0.8V. The TRACK/SS pin can be used to program an external soft-start function or to allow VOUT Alternatively, the TRACK/SS pin can be used to track two to “track” another supply during start-up. (or more) supplies during start-up, as shown qualitatively in Figures 4a and 4b. To do this, a resistor divider should Soft-start is enabled by simply connecting a capacitor be connected from the master supply (V from the TRACK/SS pin to ground, as shown in Figure 3. X) to the TRACK/ SS pin of the slave supply (V An internal 1µA current source charges up the capacitor, OUT), as shown in Figure 5. During start-up V providing a linear ramping voltage at the TRACK/SS pin. OUT will track VX according to the ratio set by the resistor divider: The LTC3834 will regulate the VFB pin (and hence VOUT) V R +R X = RA • TRACKA TRACKB LTC3834 V R R +R TRACK/SS OUT TRACKA A B CSS SGND For coincident tracking (VOUT = VX during start-up), 3834 F03 RA = RTRACKA
Figure 3. Using the TRACK/SS Pin to Program Soft-Start
RB = RTRACKB VX (MASTER) VX (MASTER) VOUT (SLAVE) VOUT (SLAVE) OUTPUT VOLTAGE OUTPUT VOLTAGE TIME 3834 F04A TIME 3834 F04B
(4a) Coincident Tracking (4b) Ratiometric Tracking Figure 4. Two Different Modes of Output Voltage Tracking
Vx VOUT RB LTC3834 VFB RA RTRACKB TRACK/SS 3834 F05 RTRACKA
Figure 5. Using the TRACK/SS Pin for Tracking
3834fc 16 For more information www.linear.com/LTC3834 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Package Description Typical Application Related Parts
APPLICATIONS INFORMATION Tracking and Soft-Start (TRACK/SS Pin)
according to the voltage on the TRACK/SS pin, allowing V The start-up of V OUT to rise smoothly from 0V to its final regulated value. OUT is controlled by the voltage on the The total soft-start time will be approximately: TRACK/SS pin. When the voltage on the TRACK/SS pin is less than the internal 0.8V reference, the LTC3834 reg- 0.8V t = C • ulates the VFB pin voltage to the voltage on the TRACK/ SS SS 1µA SS pin instead of 0.8V. The TRACK/SS pin can be used to program an external soft-start function or to allow VOUT Alternatively, the TRACK/SS pin can be used to track two to “track” another supply during start-up. (or more) supplies during start-up, as shown qualitatively in Figures 4a and 4b. To do this, a resistor divider should Soft-start is enabled by simply connecting a capacitor be connected from the master supply (V from the TRACK/SS pin to ground, as shown in Figure 3. X) to the TRACK/ SS pin of the slave supply (V An internal 1µA current source charges up the capacitor, OUT), as shown in Figure 5. During start-up V providing a linear ramping voltage at the TRACK/SS pin. OUT will track VX according to the ratio set by the resistor divider: The LTC3834 will regulate the VFB pin (and hence VOUT) V R +R X = RA • TRACKA TRACKB LTC3834 V R R +R TRACK/SS OUT TRACKA A B CSS SGND For coincident tracking (VOUT = VX during start-up), 3834 F03 RA = RTRACKA
Figure 3. Using the TRACK/SS Pin to Program Soft-Start
RB = RTRACKB VX (MASTER) VX (MASTER) VOUT (SLAVE) VOUT (SLAVE) OUTPUT VOLTAGE OUTPUT VOLTAGE TIME 3834 F04A TIME 3834 F04B
(4a) Coincident Tracking (4b) Ratiometric Tracking Figure 4. Two Different Modes of Output Voltage Tracking
Vx VOUT RB LTC3834 VFB RA RTRACKB TRACK/SS 3834 F05 RTRACKA
Figure 5. Using the TRACK/SS Pin for Tracking
3834fc 16 For more information www.linear.com/LTC3834 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Package Description Typical Application Related Parts
