Datasheet LTC7860 (Analog Devices) - 6
| Hersteller | Analog Devices |
| Beschreibung | High Efficiency Switching Surge Stopper |
| Seiten / Seite | 26 / 6 — pin FuncTions. TMR (Pin 1):. ITH (Pin 6):. FBN (Pin 7):. FREQ (Pin 2):. … |
| Dateiformat / Größe | PDF / 843 Kb |
| Dokumentensprache | Englisch |
pin FuncTions. TMR (Pin 1):. ITH (Pin 6):. FBN (Pin 7):. FREQ (Pin 2):. RUN (Pin 8):. SGND (Pin 3):. CAP (Pin 9):. SS (Pin 4):
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LTC7860
pin FuncTions TMR (Pin 1):
Programmable Fault Timer. The TMR function
ITH (Pin 6):
Current Control Threshold and Controller monitors the time spent in PROTECTIVE PWM mode and Compensation Point. This pin is the output of the error provides fault control. During a fault, a 30μA (ITPU) current amplifier and the switching regulator’s compensation pulls up the TMR pin. If the fault clears before the 1.29V point. The voltage ranges from 0V to 2.9V, with 0.8V cor- TMR Gate Off Threshold (VGTH) is reached, a 40μA current responding to zero sense voltage (zero current). (ITPDR) resets the TMR pin to ground. The gate turns off
V
and shuts down when V
FBN (Pin 7):
Feedback Input for an Inverting Feedback GTH is reached. In shutdown, a Option. Connect V 1.3μA (I FBN to the center of a resistor divider TPDC) current pulls TMR down to a 240mV TMR between the output and V Restart Threshold (V FB. The VFBN threshold is 0V. RTH) allowing a cool down period before restart. To defeat the inverting amplifier and use Non-Inverting feedback option, tie VFBN > 2V. VFBN can be tied to FREQ
FREQ (Pin 2):
Switching Frequency Setpoint Input. The if FREQ is floated and a 535kHz fixed operating frequency switching frequency is programmed by an external set- is selected. The minimum suggested value of the feedback point resistor RFREQ connected between the FREQ pin and resistor between VFB and VFBN for Inverting Feedback signal ground. An internal 20µA current source creates Option is 10K. a voltage across the external setpoint resistor to set the internal oscillator frequency. Alternatively, this pin can
RUN (Pin 8):
Run Control Input. A RUN voltage above be driven directly by a DC voltage to set the oscillator the 1.26V threshold enables normal operation, while a frequency. Grounding selects a fixed operating frequency voltage below the threshold shuts down the controller. of 350kHz. Floating selects a fixed operating frequency An internal 0.4µA current source pulls the RUN pin up to of 535kHz. about 3.3V. The RUN pin can be connected to an external power supply up to 60V.
SGND (Pin 3):
Ground Reference for Small-Signal Analog Component (Signal Ground). Signal ground should be
CAP (Pin 9):
Gate Driver (–) Supply. A low ESR ceramic used as the common ground for all small-signal analog bypass capacitor of at least 0.47µF or 10X the effective inputs and compensation components. Connect the signal CMILLER of the P-channel power MOSFET, is required ground to the power ground (ground reference for power from VIN to this pin to serve as a bypass capacitor for the components) only at one point using a single PCB trace. internal regulator. To ensure stable low noise operation, the bypass capacitor should be placed adjacent to the VIN and
SS (Pin 4):
Soft-Start and External Tracking Input. The CAP pins and connected using the same PCB metal layer. LTC7860 regulates the feedback voltage to the smaller of 0.8V or the voltage on the SS pin. An internal 10μA pull-up
SENSE (Pin 10):
Current Sense Input. A sense resistor, current source is connected to this pin. A capacitor to RSENSE, from the VIN pin to the SENSE pin sets the maxi- ground at this pin sets the ramp time to the final regulated mum current limit. The peak inductor current limit is equal output voltage. to 95mV/RSENSE. For accuracy, it is important that the VIN pin and the SENSE pin route directly to the current sense
VFB (Pin 5):
Output Feedback Sense. A resistor divider resistor and make a Kelvin (4-wire) connection. from the regulated output point to this pin sets the output voltage. The LTC7860 will nominally regulate V
V
FB to the
IN (Pin 11):
Chip Power Supply. A minimum bypass internal reference value of 0.8V. If V capacitor of 0.1µF is required from the V FB is less than 0.4V, IN pin to power the switching frequency will linearly decrease and fold ground. For best performance use a low ESR ceramic back to about one-fifth of the internal oscillator frequency capacitor placed near the VIN pin. to reduce the minimum duty cycle. 7860f 6 For more information www.linear.com/LTC7860
pin FuncTions TMR (Pin 1):
Programmable Fault Timer. The TMR function
ITH (Pin 6):
Current Control Threshold and Controller monitors the time spent in PROTECTIVE PWM mode and Compensation Point. This pin is the output of the error provides fault control. During a fault, a 30μA (ITPU) current amplifier and the switching regulator’s compensation pulls up the TMR pin. If the fault clears before the 1.29V point. The voltage ranges from 0V to 2.9V, with 0.8V cor- TMR Gate Off Threshold (VGTH) is reached, a 40μA current responding to zero sense voltage (zero current). (ITPDR) resets the TMR pin to ground. The gate turns off
V
and shuts down when V
FBN (Pin 7):
Feedback Input for an Inverting Feedback GTH is reached. In shutdown, a Option. Connect V 1.3μA (I FBN to the center of a resistor divider TPDC) current pulls TMR down to a 240mV TMR between the output and V Restart Threshold (V FB. The VFBN threshold is 0V. RTH) allowing a cool down period before restart. To defeat the inverting amplifier and use Non-Inverting feedback option, tie VFBN > 2V. VFBN can be tied to FREQ
FREQ (Pin 2):
Switching Frequency Setpoint Input. The if FREQ is floated and a 535kHz fixed operating frequency switching frequency is programmed by an external set- is selected. The minimum suggested value of the feedback point resistor RFREQ connected between the FREQ pin and resistor between VFB and VFBN for Inverting Feedback signal ground. An internal 20µA current source creates Option is 10K. a voltage across the external setpoint resistor to set the internal oscillator frequency. Alternatively, this pin can
RUN (Pin 8):
Run Control Input. A RUN voltage above be driven directly by a DC voltage to set the oscillator the 1.26V threshold enables normal operation, while a frequency. Grounding selects a fixed operating frequency voltage below the threshold shuts down the controller. of 350kHz. Floating selects a fixed operating frequency An internal 0.4µA current source pulls the RUN pin up to of 535kHz. about 3.3V. The RUN pin can be connected to an external power supply up to 60V.
SGND (Pin 3):
Ground Reference for Small-Signal Analog Component (Signal Ground). Signal ground should be
CAP (Pin 9):
Gate Driver (–) Supply. A low ESR ceramic used as the common ground for all small-signal analog bypass capacitor of at least 0.47µF or 10X the effective inputs and compensation components. Connect the signal CMILLER of the P-channel power MOSFET, is required ground to the power ground (ground reference for power from VIN to this pin to serve as a bypass capacitor for the components) only at one point using a single PCB trace. internal regulator. To ensure stable low noise operation, the bypass capacitor should be placed adjacent to the VIN and
SS (Pin 4):
Soft-Start and External Tracking Input. The CAP pins and connected using the same PCB metal layer. LTC7860 regulates the feedback voltage to the smaller of 0.8V or the voltage on the SS pin. An internal 10μA pull-up
SENSE (Pin 10):
Current Sense Input. A sense resistor, current source is connected to this pin. A capacitor to RSENSE, from the VIN pin to the SENSE pin sets the maxi- ground at this pin sets the ramp time to the final regulated mum current limit. The peak inductor current limit is equal output voltage. to 95mV/RSENSE. For accuracy, it is important that the VIN pin and the SENSE pin route directly to the current sense
VFB (Pin 5):
Output Feedback Sense. A resistor divider resistor and make a Kelvin (4-wire) connection. from the regulated output point to this pin sets the output voltage. The LTC7860 will nominally regulate V
V
FB to the
IN (Pin 11):
Chip Power Supply. A minimum bypass internal reference value of 0.8V. If V capacitor of 0.1µF is required from the V FB is less than 0.4V, IN pin to power the switching frequency will linearly decrease and fold ground. For best performance use a low ESR ceramic back to about one-fifth of the internal oscillator frequency capacitor placed near the VIN pin. to reduce the minimum duty cycle. 7860f 6 For more information www.linear.com/LTC7860