Datasheet LTC3891 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | Low IQ, 60V Synchronous Step-Down Controller |
| Pages / Page | 32 / 10 — PIN FUNCTIONS TRACK/SS (Pin 19/Pin 1):. FREQ (Pin 20/Pin 2):. FUNCTIONAL … |
| File Format / Size | PDF / 691 Kb |
| Document Language | English |
PIN FUNCTIONS TRACK/SS (Pin 19/Pin 1):. FREQ (Pin 20/Pin 2):. FUNCTIONAL DIAGRAM
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LTC3891
PIN FUNCTIONS TRACK/SS (Pin 19/Pin 1):
External Tracking and Soft-
FREQ (Pin 20/Pin 2):
The frequency control pin for the Start Input. The LTC3891 regulates the VFB voltage to the internal VCO. Connecting the pin to GND forces the VCO smaller of 0.8V or the voltage on the TRACK/SS pin. An to a fixed low frequency of 350kHz. Connecting the pin internal 10μA pull-up current source is connected to this to INTVCC forces the VCO to a fixed high frequency of pin. A capacitor to ground at this pin sets the ramp time 535kHz. Other frequencies between 50kHz and 900kHz to final regulated output voltage. Alternatively, a resistor can be programmed by using a resistor between FREQ divider on another voltage supply connected to this pin and GND. An internal 20µA pull-up current develops the allows the LTC3891 output to track another supply during voltage to be used by the VCO to control the frequency. start-up.
FUNCTIONAL DIAGRAM
INTVCC VIN + D PGOOD 0.88V BOOST B – VFB CB + DROP TG TOP OUT C – IN 0.72V DET D BOT SW TOP ON S Q INTV R Q CC SWITCH SHDN BG LOGIC BOT 20µA FREQ COUT PGND VCO CLK2 VOUT CLK1 + R 0.425V SENSE SLEEP L – ICMP IR – PFD + + – – + + – 2mV SENSE+ SYNC 2.7V PLLIN/MODE DET 0.65V SENSE– 100k SLOPE COMP ILIM VFB CURRENT + RB LIMIT EA – 0.80V VIN TRACK/SS RA + EXTV OV CC – 0.88V CC ITH 5.1V 5.1V 7µA SHDN CC2 RC LDO LDO 10µA RST FOLDBACK TRACK/SS EN EN 2(VFB) + 11V – SHDN CSS 4.7V 3891 FD SGND INTV RUN CC 3891fa 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions FUNCTIONAL Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts
PIN FUNCTIONS TRACK/SS (Pin 19/Pin 1):
External Tracking and Soft-
FREQ (Pin 20/Pin 2):
The frequency control pin for the Start Input. The LTC3891 regulates the VFB voltage to the internal VCO. Connecting the pin to GND forces the VCO smaller of 0.8V or the voltage on the TRACK/SS pin. An to a fixed low frequency of 350kHz. Connecting the pin internal 10μA pull-up current source is connected to this to INTVCC forces the VCO to a fixed high frequency of pin. A capacitor to ground at this pin sets the ramp time 535kHz. Other frequencies between 50kHz and 900kHz to final regulated output voltage. Alternatively, a resistor can be programmed by using a resistor between FREQ divider on another voltage supply connected to this pin and GND. An internal 20µA pull-up current develops the allows the LTC3891 output to track another supply during voltage to be used by the VCO to control the frequency. start-up.
FUNCTIONAL DIAGRAM
INTVCC VIN + D PGOOD 0.88V BOOST B – VFB CB + DROP TG TOP OUT C – IN 0.72V DET D BOT SW TOP ON S Q INTV R Q CC SWITCH SHDN BG LOGIC BOT 20µA FREQ COUT PGND VCO CLK2 VOUT CLK1 + R 0.425V SENSE SLEEP L – ICMP IR – PFD + + – – + + – 2mV SENSE+ SYNC 2.7V PLLIN/MODE DET 0.65V SENSE– 100k SLOPE COMP ILIM VFB CURRENT + RB LIMIT EA – 0.80V VIN TRACK/SS RA + EXTV OV CC – 0.88V CC ITH 5.1V 5.1V 7µA SHDN CC2 RC LDO LDO 10µA RST FOLDBACK TRACK/SS EN EN 2(VFB) + 11V – SHDN CSS 4.7V 3891 FD SGND INTV RUN CC 3891fa 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions FUNCTIONAL Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts
