Hello,
I am designing a circuit to work with the DLP9000X. I am basing my schematics on TI EVB schematics (attached).
on those schematics, there are circuits to for the power down procedure of the DLP9000X.
My questions are:
1. I am trying to understand each discrete circuit of the VOFFSET, VRESET, VBIAS power down on page 4(I circled them).
1.1 VOFFSET.
1.1.1 on normal mode the EN_OFFSET is '1' and thus Q3=ON which results in Q2=OFF and Q1 also OFF => VOFFSET working regular
1.1.2 on power down...EN_OFFSET is '0' and thus Q3=OFF which results in Q2=ON and thus Q1=ON => VOFFSET tied to 3.3V by D1 Zener diode? until powered down?
1.2 VRESET
1.2.1 on normal mode the EN_OFFSET is '1' and VRESET is powered (-10V per schematics) .....Q4 is OFF?! and also Q5, Q6 ....i.e: normal operation.
1.1.2 on power down...EN_OFFSET is '0' and thus Q4=ON (? not sure i understand why) which results results in Q6=ON and thus Q5=ON => VRESET tied to GND?
1.3 VBIAS.
1.1.1 on normal mode the EN_OFFSET is '1' and thus Q9=ON which results in Q8=OFF and thus Q7 also OFF => VBIAS working regular
1.1.2 on power down...EN_OFFSET is '0' and thus Q9=OFF which results in Q8=ON and thus Q7=ON => VBIAS tied to GND?
2. based on the above. May i know why I need such transistors? 2N2222 exists only in T.H form. trying to select other SMT I find that the Collector- Base Voltage VCBO of 60 V and Emitter- Base Voltage VEBO of 6V
determine that T.H package... why those figures were chosen. the reason i ask is that each of those transistors costs around $5...so the whole solution for power down estimates to around $20-$30 per board.... doesn't sound reasonable....
