Datasheet LT3652 (Analog Devices) - 21

LT3652
APPLICATIONS INFORMATION
In some cases, the thermal foldback protection feature voltage reference. Effective grounding can be achieved can reduce charger currents below the C/10 threshold. In by considering switched current in the ground plane, applications that use C/10 termination (TIMER=0V), the and careful component placement and orientation can LT3652 will suspend charging and enter standby mode effectively steer these high currents such that the battery until the excessive temperature condition is relieved. reference does not get corrupted. Figure 11 illustrates an effective grounding scheme using component placement
Layout Considerations
to control ground currents. When the switch is enabled The LT3652 switch node has rise and fall times that are (loop #1), current flows from the input bypass capacitor typically less than 10nS to maximize conversion efficiency. (CIN) through the switch and inductor to the battery posi- The switch node (Pin SW) trace should be kept as short tive terminal. When the switch is disabled (loop #2), the as possible to minimize high frequency noise. The input current to the battery positive terminal is provided from capacitor (C ground through the freewheeling Schottky diode (D IN) should be placed close to the IC to minimize F). In this switching noise. Short, wide traces on these nodes both cases, these switch currents return to ground via the also help to avoid voltage stress from inductive ringing. output bypass capacitor (CBAT). The BOOST decoupling capacitor should also be in close The LT3652 packaging has been designed to efficiently proximity to the IC to minimize inductive ringing. The remove heat from the IC via the Exposed Pad on the SENSE and BAT traces should be routed together, and backside of the package, which is soldered to a copper these and the VFB trace should be kept as short as pos- footprint on the PCB. This footprint should be made as sible. Shielding these signals from switching noise with large as possible to reduce the thermal resistance of the a ground plane is recommended. IC case to ambient air. High current paths and transients should be kept iso- lated from battery ground, to assure an accurate output CIN CBAT VBAT RSENSE 1 2 DF + LT3652 V SW IN SENSE BAT VFB 3652 F11
Figure 11. Component Orientation Isolates High Current Paths from Sensitive Nodes
3652fe For more information www.linear.com/LT3652 21 Document Outline Description Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Package Description Typical Application Related Parts