Problem 8
Choose the regulator that holds 3.3 V from 4.75–5.25 V at 0–200 mA, with 1 µF on both sides.
- The output must stay at 3.3 V in the published window from 4.75 V to 5.25 V at 0–200 mA.
- 1 µF on the input and 1 µF on the output, each to ground.
Context
A linear regulator has input, ground, and output. It holds the output only inside the range on its card. The input capacitor and the output capacitor each join their own pin to ground. This is a training model, not a vendor silicon model.
Components on this challenge
- Linear regulator. Drops a higher input to a steady 3.3 V output. The extra voltage becomes heat in this model.
- Capacitor. Stores charge and supplies a short pulse of current. With a resistor it also sets a time.
Complete the required schematic checks to unlock PCB Layout.
Full brief
Use a regulator whose card covers the input window and the load, with the input capacitor on VIN and the output capacitor on VOUT, each to ground.
How PCBGrade measures this
VIN is 5.0 V ± 0.25 V and the load is 0–200 mA. Only regulator A meets that: dropout is a constant 0.25 V and Imax is 300 mA. B is 100 mA and its dropout is not stated, so none is assumed. C is 300 mA with a constant 2.0 V dropout. Put CIN ≥ 1 µF from VIN to GND and COUT ≥ 1 µF from VOUT to GND. The library is 0.1, 1, 4.7, and 10 µF. Each capacitor terminal must be within 5.0 mm routed of its regulator pin (CIN to VIN and GND, COUT to VOUT and GND). Zones are not allowed. A via barrel on this board is 1.565 mm. The sweep is the 121-point grid VIN = (4.75 + 0.05k) V and I = 0.02j A, k and j from 0 to 10. It is an educational DC model, not SPICE: at I = 0, VOUT = min(3.3, VIN − dropout) when dropout is stated, and when I > 0 it is also limited by 3.3 × Imax / I. Every point must stay inside 3.20–3.40 V. If a capacitor is missing, under 1 µF, or farther than 5.0 mm, the result is “Outside the data-card stability conditions — output not guaranteed.” No waveform is invented. Points: regulator 20, CIN value 8, COUT value 7, sweep 25, VIN connection 5, GND connection 5, VOUT connection 5, CIN placed across the nets 3, COUT placed across the nets 2, and 5 for each of the four 5.0 mm paths. A sweep that fails, including a capacitor outside 5.0 mm, caps the score at 69.
- device/component selection · 35 pts
- simulation · 25 pts
- schematic · 20 pts
- layout · 20 pts
- Cap 69: An output that is not guaranteed inside 3.20–3.40 V caps the score at 69.
- Cap 69: Copper outside the outline cannot pass, and neither can a short between nets.
Reference
Regulator A
Passes 4.75–5.25 V in and 0–200 mA out. Dropout is a constant 0.25 V. Imax is 300 mA.
- 1. VIN. Input
- 2. GND. Ground
- 3. VOUT. Regulated output
Regulator B
Imax is 100 mA, so it cannot hold 3.3 V at 200 mA. Dropout is not stated and is not assumed.
- 1. VIN. Input
- 2. GND. Ground
- 3. VOUT. Regulated output
Regulator C
Imax is 300 mA, but dropout is a constant 2.0 V, so 4.75 V in cannot make 3.3 V out.
- 1. VIN. Input
- 2. GND. Ground
- 3. VOUT. Regulated output