Datasheet LTC3861-1 (Analog Devices) - 31

LTC3861-1
applicaTions inFormaTion
To set the output voltage equal to 1.2V: 3. The PCB traces for remote voltage and current sense R should avoid any high frequency switching nodes in FB1 = 10k, RFB2 = 10k the circuit and should ideally be shielded by ground The LTC4449 gate driver and external MOSFETs are chosen planes. Each pair (VSNSP and VSNSN, ISNSP and for the power stage. DrMOSs from Fairchild, Infineon, ISNSN) should be routed parallel to one another with Vishay and others can also be used. minimum spacing between them. If DCR sensing is used, place the top resistor (Figure 5b, R1) close to
Printed Circuit Board Layout Checklist
the switching node. When laying out the printed circuit board, the following 4. The input capacitor should be kept as close as possible checklist should be used to ensure proper operation of to the power MOSFETs. The loop from the input capaci- the converter. tor’s positive terminal, through the MOSFETs and back 1. The connection between the SGND pin on the LTC3861-1 to the input capacitor’s negative terminal should also and all of the small-signal components surrounding the be as small as possible. IC should be isolated from the system power ground. 5. If using discrete drivers and MOSFETs, check the Place all decoupling capacitors, such as the ones on stress on the MOSFETs by independently measuring VCC, between ISNSP and ISNSN etc., close to the IC. In the drain-to-source voltages directly across the device multiphase operation SGND should be Kelvin-connected terminals. Beware of inductive ringing that could exceed to the main ground node near the bottom terminal of the maximum voltage rating of the MOSFET. If this the input capacitor. In dual-channel operation, SGND ringing cannot be avoided and exceeds the maximum should be Kelvin-connected to the bottom terminal of rating of the device, choose a higher voltage rated the output capacitor for channel 2, and channel 1 should MOSFET. be remotely sensed using the remote sense differential amplifier. 6. When cascading multiple LTC3861-1 ICs, minimize the capacitive load on the CLKOUT pin to minimize 2. Place the small-signal components away from high fre- phase error. Kelvin all the LTC3861-1 IC grounds to quency switching nodes on the board. The LTC3861-1 the same point, typically SGND of the IC containing contains remote sensing of output voltage and inductor the master. current and logic-level PWM outputs enabling the IC to be isolated from the power stage. 38611fb For more information www.linear.com/LTC3861-1 31 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 Typical Applications Package Description Related Parts