Datasheet LTC3708 (Analog Devices) - 9
| Hersteller | Analog Devices |
| Beschreibung | Fast 2-Phase, No RSENSE Buck Controller with Output Tracking |
| Seiten / Seite | 34 / 9 — PIN FUNCTIONS. RUN/SS (Pin 1):. PGND1, PGND2 (Pins 23, 19):. SENSE1–, … |
| Dateiformat / Größe | PDF / 667 Kb |
| Dokumentensprache | Englisch |
PIN FUNCTIONS. RUN/SS (Pin 1):. PGND1, PGND2 (Pins 23, 19):. SENSE1–, SENSE2– (Pins 24, 18):. ITH1, ITH2 (Pins 2, 8):
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LTC3708
PIN FUNCTIONS RUN/SS (Pin 1):
Run Control and Soft-Start Input. A
PGND1, PGND2 (Pins 23, 19):
Power Ground. Connect this capacitor to ground at this pin sets the ramp rate of the pin closely to the source of the bottom N-channel MOSFET, output voltage (approximately 0.5s/µF) and the time delay the (–) terminal of CDRVCC and the (–) terminal of CIN. for overcurrent latchoff (see Applications Information). Forcing this pin below 0.8V shuts down the LTC3708.
SENSE1–, SENSE2– (Pins 24, 18):
Current Sense Com- parator Input. The (–) input to the current comparator is
ITH1, ITH2 (Pins 2, 8):
Error Amplifier Compensation Point used to accurately Kelvin sense the bottom side of the and Current Control Threshold. The current comparator sense resistor or MOSFET. threshold increases with this control voltage. The voltage ranges from 0V to 2.4V with 0.8V corresponding to zero
SENSE1+, SENSE2+ (Pins 25, 16):
Current Sense Com- sense voltage (zero current). parator Input. The (+) input to the current comparator is normally connected to the SW node unless using a sense
VFB1, VFB2 (Pins 3, 7):
Error Amplifier Feedback Input. resistor (See Applications Information). This pin connects the error amplifier input to an external resistive divider from V
SW1, SW2 (Pins 26, 15):
Switch Node. The (–) terminal of OUT . Additional compensation can be implemented, if desired, using this pin. the bootstrap capacitor CB connects here. This pin swings from a Schottky diode voltage drop below ground up to VIN.
TRACK1, TRACK2 (Pins 4, 6):
Tie TRACK2 pin to a re- sistive divider connected to the output of channel 1 for
TG1, TG2 (Pins 27, 14):
Top Gate Drive. Drives the top either coincident or ratiometric output tracking. TRACK1 N-channel MOSFET with a voltage swing equal to DRVCC is used in the same manner between multiple LTC3708s superimposed on the switch node voltage SW. (see Applications Information). To disable this feature, tie
BOOST1, BOOST2 (Pins 28, 13):
Boosted Floating Driver the pins to VCC. Do Not Float These Pins. Supply. The (+) terminal of the bootstrap capacitor CB
SGND (Pins 5, 33):
Signal Ground. All small-signal com- connects here. This pin swings from a diode voltage drop ponents and compensation components should connect to below DRVCC up to VIN + DRVCC. this ground and eventually connect to PGND at one point.
ION1, ION2 (Pins 29, 12):
On-Time Current Input. Tie a The Exposed Pad of the LTC3708EUH must be soldered resistor from VIN to this pin to set the one-shot timer to the PCB. current and thereby set the switching frequency.
EXTLPF (Pin 9):
Filter Connection for the External PLL.
PGOOD (Pin 30):
Power Good Output. Open-drain logic This PLL is used to synchronize the LTC3708 to an external output that is pulled to ground when either or both output clock. If external clock is not used, leave this pin floating. voltages are not within ±10% of the regulation point. The
INTLPF (Pin 10):
Filter Connection for the Internal PLL. output voltage must be out of regulation for at least 100µs This PLL is used to phase shift the second channel to the before the power good output is pulled to ground. first channel by 180°.
FCB (Pin 31):
Forced Continuous and External Clock Input.
V
Tie this pin to ground to force continuous synchronous
CC (Pin 17):
Main Input Supply. Decouple this pin to SGND with an RC filter (10Ω, 1µF for example). operation or to VCC to enable discontinuous mode opera- tion at light load. Feeding an external clock signal into this
DRVCC (Pin 21):
Driver Supply. Provides supply to the pin will synchronize the LTC3708 to the external clock and drivers for the bottom gates. Also used for charging the enable forced continuous mode. bootstrap capacitors.
VRNG1, VRNG2 (Pins 32, 11):
Sense Voltage Range Input.
BG1, BG2 (Pins 22, 20):
Bottom Gate Drive. Drives the The voltage at this pin is ten times the nominal sense volt- gate of the bottom N-channel MOSFET between ground age at maximum output current and can be programmed and DRVCC. from 0.5V to 2V. The sense voltage defaults to 70mV when this pin is tied to ground, 140mV when tied to VCC. 3708fc For more information www.linear.com/LTC3708 9 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Applications Information Package Description Typical Application Related Parts
PIN FUNCTIONS RUN/SS (Pin 1):
Run Control and Soft-Start Input. A
PGND1, PGND2 (Pins 23, 19):
Power Ground. Connect this capacitor to ground at this pin sets the ramp rate of the pin closely to the source of the bottom N-channel MOSFET, output voltage (approximately 0.5s/µF) and the time delay the (–) terminal of CDRVCC and the (–) terminal of CIN. for overcurrent latchoff (see Applications Information). Forcing this pin below 0.8V shuts down the LTC3708.
SENSE1–, SENSE2– (Pins 24, 18):
Current Sense Com- parator Input. The (–) input to the current comparator is
ITH1, ITH2 (Pins 2, 8):
Error Amplifier Compensation Point used to accurately Kelvin sense the bottom side of the and Current Control Threshold. The current comparator sense resistor or MOSFET. threshold increases with this control voltage. The voltage ranges from 0V to 2.4V with 0.8V corresponding to zero
SENSE1+, SENSE2+ (Pins 25, 16):
Current Sense Com- sense voltage (zero current). parator Input. The (+) input to the current comparator is normally connected to the SW node unless using a sense
VFB1, VFB2 (Pins 3, 7):
Error Amplifier Feedback Input. resistor (See Applications Information). This pin connects the error amplifier input to an external resistive divider from V
SW1, SW2 (Pins 26, 15):
Switch Node. The (–) terminal of OUT . Additional compensation can be implemented, if desired, using this pin. the bootstrap capacitor CB connects here. This pin swings from a Schottky diode voltage drop below ground up to VIN.
TRACK1, TRACK2 (Pins 4, 6):
Tie TRACK2 pin to a re- sistive divider connected to the output of channel 1 for
TG1, TG2 (Pins 27, 14):
Top Gate Drive. Drives the top either coincident or ratiometric output tracking. TRACK1 N-channel MOSFET with a voltage swing equal to DRVCC is used in the same manner between multiple LTC3708s superimposed on the switch node voltage SW. (see Applications Information). To disable this feature, tie
BOOST1, BOOST2 (Pins 28, 13):
Boosted Floating Driver the pins to VCC. Do Not Float These Pins. Supply. The (+) terminal of the bootstrap capacitor CB
SGND (Pins 5, 33):
Signal Ground. All small-signal com- connects here. This pin swings from a diode voltage drop ponents and compensation components should connect to below DRVCC up to VIN + DRVCC. this ground and eventually connect to PGND at one point.
ION1, ION2 (Pins 29, 12):
On-Time Current Input. Tie a The Exposed Pad of the LTC3708EUH must be soldered resistor from VIN to this pin to set the one-shot timer to the PCB. current and thereby set the switching frequency.
EXTLPF (Pin 9):
Filter Connection for the External PLL.
PGOOD (Pin 30):
Power Good Output. Open-drain logic This PLL is used to synchronize the LTC3708 to an external output that is pulled to ground when either or both output clock. If external clock is not used, leave this pin floating. voltages are not within ±10% of the regulation point. The
INTLPF (Pin 10):
Filter Connection for the Internal PLL. output voltage must be out of regulation for at least 100µs This PLL is used to phase shift the second channel to the before the power good output is pulled to ground. first channel by 180°.
FCB (Pin 31):
Forced Continuous and External Clock Input.
V
Tie this pin to ground to force continuous synchronous
CC (Pin 17):
Main Input Supply. Decouple this pin to SGND with an RC filter (10Ω, 1µF for example). operation or to VCC to enable discontinuous mode opera- tion at light load. Feeding an external clock signal into this
DRVCC (Pin 21):
Driver Supply. Provides supply to the pin will synchronize the LTC3708 to the external clock and drivers for the bottom gates. Also used for charging the enable forced continuous mode. bootstrap capacitors.
VRNG1, VRNG2 (Pins 32, 11):
Sense Voltage Range Input.
BG1, BG2 (Pins 22, 20):
Bottom Gate Drive. Drives the The voltage at this pin is ten times the nominal sense volt- gate of the bottom N-channel MOSFET between ground age at maximum output current and can be programmed and DRVCC. from 0.5V to 2V. The sense voltage defaults to 70mV when this pin is tied to ground, 140mV when tied to VCC. 3708fc For more information www.linear.com/LTC3708 9 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Applications Information Package Description Typical Application Related Parts