{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

# ch3hwsol - Embedded Controller Design W00 Problem Solutions...

This preview shows pages 1–2. Sign up to view the full content.

Embedded Controller Design, W00 Problem Solutions 4 Solutions to Chapter 3 Problems For the following problems, refer to the loading example and Figure 3-15. 1. A) If a 10K pull-up resistor is used, how many additional LSTTL loads can be connected? B) How many CMOS loads could be added? When the LSTTL driver's output is 0: The output is assumed to be at 0.4 volts. This is max V(ol), and represents a noise margin of 0.4 volts from V(il) max of the CMOS and LSTTL loads. The CMOS gate input is sourcing a negligible amount of leakage current--less than 1 uA. The LSTTL gate input is sourcing as much as 360 uA (I(il) max) to the LSTTL output. The voltage across the 10k resistor is 4.6 volts (Vcc - V(ol) max). Therefore the current sunk by the LSTTL output is (4.6/10k) + 360 uA = 820 uA. The LSTTL output is specified to sink at least 3.2 mA and maintain V(ol) max, so it can sink an additional 3.2 - .820 = 2.38 mA. Since each additional LSTTL input would source 360 uA, the 2.38-mA excess sink capability of the LSTTL input represents 2.38/0.36 = 6 additional inputs. When the LSTTL driver's output is 1: The output is assumed to be at 3.4 volts; the min V(ih) for the CMOS device (3.0v), plus the same 0.4 volt noise margin that applies to the TTL signals. This represents a voltage drop of 1.6 volts across the 10k resistor. By Ohm's law, that's a current flow of 160 uA. The CMOS gate input is sinking a negligible amount of leakage current--less than 1 uA. The LSTTL gate input is sinking 60 uA of the 160 available. The excess source capability is 160 - 60 = 100 uA. Since each additional LSTTL input would require 60 uA, the circuit can support only one more LSTTL input, which is more restrictive than the logic 0 case above.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 3

ch3hwsol - Embedded Controller Design W00 Problem Solutions...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online