Datasheet LTC3878 (Analog Devices) - 7

LTC3878 pin FuncTions
RUN/SS (Pin 1):
Run Control and Soft-Start Input. A
VFB (Pin 8):
Error Amplifier Feedback Input. This pin con- capacitor to ground on this pin sets the ramp time to full nects the error amplifier to an external resistive divider output current (approximately 3s/µF) when RUN/SS is from VOUT. open. The switching outputs are disabled when below 1.5V.
NC (Pin 9):
For factory use only. Can be connected to any The device is in micropower shutdown when under 0.7V. voltage equal to or less than INTV If left open, there is an internal 1.2µA pull-up current on CC. RUN/SS. INTVCC is enabled when RUN/SS exceeds 0.7V.
VIN (Pin 10):
Main Input Supply. The supply voltage can range from 4V to 38V. For increased noise immunity de-
PGOOD (Pin 2):
Power Good Output. This open-drain couple this pin to PGND with an RC filter. logic output is pulled to ground when the output voltage is outside of a ±7.5% window around the regulation point.
INTVCC (Pin 11):
Internal 5.3V Regulator Output. The driver and control circuits are powered from this voltage.
VRNG (Pin 3):
VDS Sense Voltage Range Input. The maxi- Decouple this pin to PGND with a minimum of 1µF, 10V mum allowed bottom MOSFET VDS sense voltage between X5R or X7R ceramic capacitor. SW and PGND is equal to (0.133)VRNG. The voltage applied to VRNG can be any value between 0.2V and 2V. If VRNG is
BG (Pin 12):
Bottom Gate Drive. This pin drives the gate tied to SGND, the device operates with a maximum valley of the bottom N-Channel power MOSFET between PGND current sense threshold of 93mV typical. If VRNG is tied and INTVCC. to INTVCC, the device operates with a maximum valley
PGND (Pin 13):
Power Ground. Connect this pin as close current sense threshold of 186mV typical. as practical to the source of the bottom N-channel power
FCB (Pin 4):
Forced Continuous Input. Connect this pin MOSFET, the (–) terminal of CINTVCC and the (–) terminal to INTVCC to enable discontinuous mode for light load of CVIN. operation. Connect this pin to SGND to force continuous
SW (Pin 14):
Switch Node. The (–) terminal of the bootstrap mode operation in all conditions. capacitor, CB, connects to this node. This pin swings from
ITH (Pin 5):
Current Control Threshold and Error Amplifier a diode voltage below ground up to VIN. Compensation Point. The current comparator threshold
TG (Pin 15):
Top Gate Drive. This pin drives the gate of the increases with this control voltage. The voltage ranges top N-channel power MOSFET between SW and BOOST. from 0V to 2.4V, with 0.8V corresponding to zero sense voltage (zero current).
BOOST (Pin 16):
Boosted Floating Driver Supply. The (+) terminal of the bootstrap capacitor, C
SGND (Pin 6):
Signal Ground. Al smal -signal components B, connects to this node. This node swings from (INTV should be connected to SGND. Connect SGND to PGND CC – VSCHOTTKY) to V using a single PCB trace. IN + (INTVCC – VSCHOTTKY).
ION (Pin 7):
On-Time Current Input. Tie a resistor from VIN to this pin to set the one-shot timer current and thus the switching frequency. 3878fa Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration order information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts