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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