L5988DTR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
L5988DTR
STMicroelectronics
L5988DTR Datasheet PDF : 52 Pages
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L5988D
Application information
Figure 23. Measurement of the thermal impedance of the evaluation board
As it can be see, for example, for load pulses with duration of 1 second, the actual thermal
impedance is lower than 20 C/W. This means that, for short pulses, a current higher that
5 A (provided the current limitation is set correctly) can be managed.
6.7
Layout considerations
The PC board layout of switching DC/DC regulator is very important to minimize the noise
injected in high impedance nodes and interferences generated by the high switching current
loops. The L5988D is a monolithic device so most of the critical path are designed internally
minimizing the potential issues introduced by the board layout.
In the operation of a step down converter two high current loops become evident and
critical. The conduction of the high side switch highlight a current loop composed by the
input capacitor, the inductor and the output capacitor whilst during the conduction of the low
side switch the current flows from the power ground to the inductor and again the output
capacitor.
The first consideration is to keep the trace of the switching node as short as possible to
reduce radiated emission.
The bandwidth of the external power supply is limited if compared to the switching
frequency of the device so the power supply delivers a certain RMS current in the switching
period. As a consequence the input filter substains the input voltage during the conduction
time of the HS switch delivering an impulsive extra current equal to ILOAD + IRIPPLE - IIN RMS
and it is recharged during the conduction time of the low side by the external power supply.
The golden rule is to reduce as much as possible the stray inductance of the path related to
the capacitor and VINto reduce injected noise: the suggested layout (see Figure 24 and
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