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Application Note 10.8
USB97C223 and USB97C243
Capacitor Selection for Internal Regulator Output Pins
SMSC AN 10.8
Rev. 12-16-03
APPLICATION NOTE
USB97C223 and USB97C243 Capacitor Selection for Internal Regulator Output Pins
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SMSC AN 10.8
Page 2
Rev. 12-16-03
APPLICATION NOTE
USB97C223 and USB97C243 Capacitor Selection for Internal Regulator Output Pins
Overview
The USB97C223 and USB97C243 have two internal 1.8V regulators used to provide the digital and analog 1.8V supplies. The output pins of the regulator have very specific capacitor requirements that are described below. It is important that the customer designs their product with the specifications set forth in this document.
Requirements
Table 1 lists the capacitor requirements on the regulator output pins. Table 1 - Regulator Output Pins PIN NUMBER 98 91 PIN NAME VDDP VDDCORE USB97C223 PIN DESCRIPTION Analog Regulator Output Digital Regulator Output USB97C243 Analog Regulator Output Digital Regulator Output CAPACITOR REQUIREMENT 10uF +/- 20 % with < 0.65 Ohm ESR 10uF +/- 20 % with < 0.65 Ohm ESR
50 43
VDDP VDDCORE (closest to VREG)
10uF +/- 20 % with < 0.65 Ohm ESR 10uF +/- 20 % with < 0.65 Ohm ESR
Figure 1 and Figure 2 show an example of the degradation in performance of the USB97C223 and USB97C243 as the ESR of the capacitor on the output of the regulators is increased to 0.65 Ohm.
Figure 1 - 10uF Capacitor with 0.1 Ohm ESR
Figure 2 - 10uF Capacitor with 0.65 Ohm ESR
SMSC AN 10.8
Page 3
Rev. 12-16-03
APPLICATION NOTE
USB97C223 and USB97C243 Capacitor Selection for Internal Regulator Output Pins
SMSC recommends the use of ceramic 10uF capacitors to meet the low ESR requirements of the regulator output pins of the USB97C223. Ceramic capacitors typically have an ESR of < 0.1 Ohm. Recommended Capacitors, or equivalent: Kemet C0805C106K9PACTU Kemet C1206C106K9PACTU Panasonic ECJ-2FF0J106Z Panasonic ECJ-2FF1A106Z (0805 Package) (1206 Package) (0805 Package) (0805 Package)
Tantalum capacitors that have low ESR specifications can also be used, but typically have an ESR closer to 0.5 Ohm.
SMSC AN 10.8
Page 4
Rev. 12-16-03
APPLICATION NOTE

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