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Regulators

Linear regulators provide VDDD and VDDA for each module connected to the SURF board. Fig. 3.1 shows the two regulators supplying each module. The resistor R?/R? current-limits the regulators to

\begin{displaymath}I_{\rm max} = \frac{57 {\rm\ mV}}{R_{\rm s}} = 1.5 {\rm\ A}.\end{displaymath}

The capacitor-diode network blah blah blah makes the output voltage ramp when the regulator is enabled.

The EZ-USB processor on the SURF board (Sec. 3.6) can set the voltage level of each regulator by talking to the digital potentiometers (U?); the processor can also disable each regulator entirely. Fig. 3.4 shows a plot of analog and digital supply voltage as a function of potentiometer resistance ($R_{\rm v}$).

Figure 3.1: Regulator schematic
\begin{figure}\epsfysize =0.9\textheight\centering\epsfbox{fanout11107.epsi}\end{figure}

Figure 3.2: LP2975 schematic[#!lp2975!#]. $R_{\rm set} = 39.9$ k$\Omega $.
\begin{figure}\centering\epsfbox{LP2975.epsi}\end{figure}

Figure 3.3: LP2975 schematic[#!lp2975!#]. $R_{\rm set} = 39.9$ k$\Omega $.

Figure 3.4: The dependence on the high-tolerance (20%) internal 24-k$\Omega $ resistor is shown. The solid line indicates 0% deviation from 24 k$\Omega $, the dashed lines $\pm 10$% and the dotted lines $\pm 20$%.
\begin{figure}\centering\epsfxsize =\textwidth\epsfbox{vdd.eps}\end{figure}

next up previous contents
Next: Temperature interlock Up: Hacking the hardware Previous: Hacking the hardware   Contents
Johannes Muelmenstaedt 2004-03-31