Datasheet LT3697 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | USB 5V, 2.5A Output, 35V Input Buck with Cable Drop Compensation |
| Pages / Page | 32 / 9 — pin FuncTions VIN (Pins 1, 2):. RCBL (Pin 9):. EN (Pin 3):. FLT (Pin 4):. … |
| File Format / Size | PDF / 451 Kb |
| Document Language | English |
pin FuncTions VIN (Pins 1, 2):. RCBL (Pin 9):. EN (Pin 3):. FLT (Pin 4):. ISN (PIN 10):. SYNC (Pin 5):. ISP (Pin 11):. RT (Pin 6):
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LT3697
pin FuncTions VIN (Pins 1, 2):
The VIN pins supply current to the LT3697’s 99.5% of the current limit for at least 1.5ms, the LT3697 internal regulator and to the power switch. These pins will pull down on the FLT pin. Float the RLIM pin if not used. must be locally bypassed.
RCBL (Pin 9):
The RCBL pin is used to program the USB5V
EN (Pin 3):
The EN pin is used to put the LT3697 into current as a function of sense voltage (VISP – VISN) for shutdown mode. Tie to ground to shut down the LT3697. cable drop compensation. Tie a resistor from RCBL to Tie to 2.5V or higher for normal operation. If the shutdown ground to set the USB5V input current. Float the RCBL feature is not used, tie this pin to the VIN pin. pin if cable drop compensation is not desired. The RCBL
FLT (Pin 4):
The FLT pin is the open drain output of the pin may also be used as an USB output current monitor. LT3697 fault comparator and timer. In normal operation Excessive capacitive loading on the RCBL pin can cause the FLT pin is high impedance. An overcurrent fault that USB output voltage overshoot during load steps when is sustained for at least 1.5ms causes the LT3697 to pull cable drop compensation is used. Keep the capacitive the FLT pin low. The FLT pin then remains low until the loading on the RCBL pin below 100pF. USB output current stays below the overcurrent threshold
ISN (PIN 10):
The ISN pin is the inverting input of the for at least 1.5ms. The overcurrent fault threshold is 0.5% LT3697’s onboard USB output current sense amplifier. below the current limit. The FLT output is valid when VIN Tie a resistor RSENSE from ISP to ISN to sense the USB is above 4V and EN is high. output current. Connect ISN to ISP if the current monitor,
SYNC (Pin 5):
The SYNC pin is the external clock synchro- USB output current limit, and cable drop compensation nization input. Tie to a clock source with on and off times functions are not desired. greater than 50ns for synchronization. Tie pin to ground if
ISP (Pin 11):
The ISP pin is the noninverting input of the not used. See the Synchronization section in Applications LT3697’s onboard USB output current sense amplifier. Tie Information for more details. a resistor RSENSE from ISP to ISN to sense the USB output
RT (Pin 6):
The RT pin is the oscillator resistor input. current. When a USB switch is used in series between Connect a resistor from this pin to ground to set the the LT3697 and the 5V USB output, tie the ISP pin to the switching frequency. USB switch output.
VC (Pin 7):
The VC pin is the output of the internal error
USB5V (Pin 12):
The USB5V pin is the primary feedback amplifier. The voltage on this pin controls the peak switch input of the internal error amplifier. In normal operation, current. Tie an R-C network from this pin to ground to the LT3697 regulates the voltage on this pin to 5V. The compensate the control loop. USB5V pin also allows the output voltage to increase as a function of output current to compensate for voltage drop
RLIM (Pin 8):
The RLIM pin provides an additional reference at the point of load due to cable impedance. The USB5V to the third feedback amplifier of the LT3697 to allow the pin input current is proportional to USB output current output current limit to be programmed easily. The RLIM and is programmed by the RCBL resistor. Tie a resistor pin has an accurate 11μA pull-up current. When the voltage from USB5V to the 5V USB output to set this cable drop of the output current sense amplifier exceeds the lower compensation. of the RLIM voltage or 1.22V, the LT3697 error amplifier will switch to current limit mode and will regulate the USB Tie USB5V directly to the USB output if no cable drop output current. In current limit mode, the output voltage compensation is desired. If a USB switch is used in se- drops. Tie a resistor from RLIM to ground to program the ries between the LT3697 and the 5V USB output, tie the LT3697 current limit. If the USB output current exceeds USB5V pin through the compensation resistor to the USB switch output. 3697f 9 For more information www.linear.com/LT3697
pin FuncTions VIN (Pins 1, 2):
The VIN pins supply current to the LT3697’s 99.5% of the current limit for at least 1.5ms, the LT3697 internal regulator and to the power switch. These pins will pull down on the FLT pin. Float the RLIM pin if not used. must be locally bypassed.
RCBL (Pin 9):
The RCBL pin is used to program the USB5V
EN (Pin 3):
The EN pin is used to put the LT3697 into current as a function of sense voltage (VISP – VISN) for shutdown mode. Tie to ground to shut down the LT3697. cable drop compensation. Tie a resistor from RCBL to Tie to 2.5V or higher for normal operation. If the shutdown ground to set the USB5V input current. Float the RCBL feature is not used, tie this pin to the VIN pin. pin if cable drop compensation is not desired. The RCBL
FLT (Pin 4):
The FLT pin is the open drain output of the pin may also be used as an USB output current monitor. LT3697 fault comparator and timer. In normal operation Excessive capacitive loading on the RCBL pin can cause the FLT pin is high impedance. An overcurrent fault that USB output voltage overshoot during load steps when is sustained for at least 1.5ms causes the LT3697 to pull cable drop compensation is used. Keep the capacitive the FLT pin low. The FLT pin then remains low until the loading on the RCBL pin below 100pF. USB output current stays below the overcurrent threshold
ISN (PIN 10):
The ISN pin is the inverting input of the for at least 1.5ms. The overcurrent fault threshold is 0.5% LT3697’s onboard USB output current sense amplifier. below the current limit. The FLT output is valid when VIN Tie a resistor RSENSE from ISP to ISN to sense the USB is above 4V and EN is high. output current. Connect ISN to ISP if the current monitor,
SYNC (Pin 5):
The SYNC pin is the external clock synchro- USB output current limit, and cable drop compensation nization input. Tie to a clock source with on and off times functions are not desired. greater than 50ns for synchronization. Tie pin to ground if
ISP (Pin 11):
The ISP pin is the noninverting input of the not used. See the Synchronization section in Applications LT3697’s onboard USB output current sense amplifier. Tie Information for more details. a resistor RSENSE from ISP to ISN to sense the USB output
RT (Pin 6):
The RT pin is the oscillator resistor input. current. When a USB switch is used in series between Connect a resistor from this pin to ground to set the the LT3697 and the 5V USB output, tie the ISP pin to the switching frequency. USB switch output.
VC (Pin 7):
The VC pin is the output of the internal error
USB5V (Pin 12):
The USB5V pin is the primary feedback amplifier. The voltage on this pin controls the peak switch input of the internal error amplifier. In normal operation, current. Tie an R-C network from this pin to ground to the LT3697 regulates the voltage on this pin to 5V. The compensate the control loop. USB5V pin also allows the output voltage to increase as a function of output current to compensate for voltage drop
RLIM (Pin 8):
The RLIM pin provides an additional reference at the point of load due to cable impedance. The USB5V to the third feedback amplifier of the LT3697 to allow the pin input current is proportional to USB output current output current limit to be programmed easily. The RLIM and is programmed by the RCBL resistor. Tie a resistor pin has an accurate 11μA pull-up current. When the voltage from USB5V to the 5V USB output to set this cable drop of the output current sense amplifier exceeds the lower compensation. of the RLIM voltage or 1.22V, the LT3697 error amplifier will switch to current limit mode and will regulate the USB Tie USB5V directly to the USB output if no cable drop output current. In current limit mode, the output voltage compensation is desired. If a USB switch is used in se- drops. Tie a resistor from RLIM to ground to program the ries between the LT3697 and the 5V USB output, tie the LT3697 current limit. If the USB output current exceeds USB5V pin through the compensation resistor to the USB switch output. 3697f 9 For more information www.linear.com/LT3697
