TPS74701-Q1: LDO Output Accuracy Calculation

Hi Evan,

Sorry for the delayed response.

Devices like this one that have only typical values for the line/load regulation are difficult to calculate the worst case, but here's how I would approach narrowing the spec. 

Evan Wang said:

Scenario 1:

• VIN: 3.3V
• VOUT: 1.2V
• VBIAS: 5V
• IOUT: 250mA

Actual load reg = 0.11%/A * (250mA - 50mA) = 0.022% (typ)

Actual line reg = 0.001%/V * (3.3V - (1.2V + 0.3V)) = .0018% (typ)

Total VOUT spec = 1.25% - 0.022% - 0.0018% = 1.226%

Since the line and load specs are typical values, which are at Tj = 25C, the specs do not include temperature or process variation and so the overall accuracy spec is not narrowed by much. 

Evan Wang said:

Scenario 2:

• VIN: 5V
• VOUT: 1.8V
• VBIAS: 5V
• IOUT: 100mA

Actual load reg = 0.11%/A * (100mA - 50mA) = 0.0055% (typ)

Actual line reg = 0.001%/V * (5V - (1.8V + 0.3V)) = .0029% (typ)

Total VOUT spec = 1.25% - 0.0055% - 0.0029% = 1.242%

This would be the approach for other devices as well, but for this device the typical line/load reg specs limit how much the accuracy spec can be narrowed. With that said, 1.25% over all operating conditions is already pretty tight for an LDO.

Regards,

Nick