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PCA9620 датащи(PDF) 34 Page - NXP Semiconductors |
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PCA9620 датащи(HTML) 34 Page - NXP Semiconductors |
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34 / 71 page ![]() PCA9620 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved. Product data sheet Rev. 1 — 9 December 2010 34 of 71 NXP Semiconductors PCA9620 Universal LCD driver for low multiplex rates (9) The ratio between these two numbers determines the charge pump power efficiency: (10) Loading the charge pump with higher currents decreases the output voltage. This decrease is determined by the charge pump driving capability, respectively by the output resistance of the charge pump (see Table 35 on page 55). The power efficiency calculation is only valid when the charge pump is running at its maximum peak frequency and regulates the generated VLCD voltage with full speed. In this case, the ripple on the VLCD voltage equals the internal charge pump frequency. Approximately, this could also be calculated with the parameter of the output resistance of the charge pump (see Table 35 on page 55), the load current, and the voltage needed to be provided by using Equation 7 on page 33. This value of Iload is close to the value of the load current needed for the application. If the application runs with VDD2 = 3.0 V, the load currents are up to 400 μA (DC measured), and the VLCD generated voltages are up to 5.0 V, then - concerning power efficiency - it would be the best to have a charge pump frequency set to half frequency. Charge pump set to 2 × V DD2; VDD2 =3V. (1) η p, full charge pump frequency. (2) η p, half charge pump frequency. (3) VLCD, full frequency. (4) VLCD, half frequency. Fig 26. Power efficiency of the charge pump P i I DD2 V DD2 × = η p P o Pi ⁄ = Iload (μA) 0 1000 800 400 600 200 001aan027 50 70 90 ηp (%) 30 3 5 7 VLCD (V) 1 (3) (4) (1) (2) |
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