LP2950-N, LP2951-N
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SNVS764Q –JANUARY 2000–REVISED DECEMBER 2017
Layout Example (continued)
Ground
Output
Input
Capacitor
Capacitor
Exposed
Thermal Pad
IN
1
2
3
4
8
VIN
OUT
SENSE
VOUT
7
FEEDBACK
VTAP
SHUTDOWN
6
5
Error Pullup
Resistor
6 Thermal Vias
Ground
ERROR
VOUT
GND
Figure 58. LP2951 WSON Board Layout
11.3 WSON Mounting
The NGT (no pullback) 8-lead WSON package requires specific mounting techniques which are detailed in AN-
1187 Leadless Leadframe Package (LLP). Referring to the PCB Design Recommendations section, note that the
pad style which should be used with the WSON package is the NSMD (non-solder mask defined) type.
Additionally, TI recommends that the PCB terminal pads to be 0.2 mm longer than the package pads to create a
solder fillet to improve reliability and inspection.
The thermal dissipation of the WSON package is directly related to the printed circuit board construction and the
amount of additional copper area connected to the DAP.
For the LP2951-N in the NGT 8-lead WSON package, the junction-to-case thermal rating, RθJC, is 35°C/W, where
the case is the bottom of the package at the center of the DAP.
The DAP (exposed pad) on the bottom of the WSON package is connected to the die substrate with a conductive
die attach adhesive. The DAP has no direct electrical (wire) connection to any of the eight pins. There is a
parasitic PN junction between the die substrate and the device ground. As such, it is strongly recommend that
the DAP be connected directly to the ground at device lead 4 (that is, GND). Alternately, but not recommended,
the DAP may be left floating (that is, no electrical connection). The DAP must not be connected to any potential
other than ground.
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