Notification 227 - High output ripple current: High ripple, low ESR Capacitors required

CATEGORY

ISSUE / RESULT

FIX / REFERENCE(S)

Information

One or more output capacitors will be required to decouple high ripple currents (IO 4.0 A).  Therefore, the ripple current capacity and ESR of the output capacitors used on those outputs should be verified before considering this design manufacturable.

Subjecting Aluminum Electrolytic capacitors to excessive ripple current can reduce their expected life span significantly and lead to premature aging and failure.

  • Measure the output capacitor case, at the maximum ambient temperature, on a prototype PCB.  Case temperatures should not exceed +70 °C).

  • Verify that the ripple current rating of the output capacitors meets the expected life span requirement (see IRIP calculation and Table 1 for common high-ripple/low ESR output capacitor ripple current ratings).

  • To force equal ripple current sharing, layouts need consistent path lengths and widths (equal impedance) between the transformer and the output capacitors; see Figure 1.

  • See Application Note AN-26 (-FX)  or AN-32 (-GX)  and Appendix A for details on IRIP calculations.

 

Various high-ripple current rated Aluminum Electrolytic capacitor manufacturers and model numbers

Manufacturer

Type

Capacitance / Voltage / Temperature

Size

(¢DxL)

Max Temp., 100 kHz

Ripple Rating (Irms)

Panasonic

FC

1000 mF / 35 V / 105 °C

12.5 x 25 mm

1945 mA

 

HFQ

1000 mF / 35 V / 105 °C

12.5 x 30 mm

1950 mA

United Chemicon - Marcon

LXY

220 mF / 25 V / 105 °C

8 x 12 mm

555 mA

 

LXZ

220 mF / 25 V / 105 °C

8 x 15 mm

555 mA

Nichicon

PF

560 mF / 35 V / 105 °C

12.5 x 20 mm

855 mA

 

PL

560 mF / 35 V / 105 °C

12.5 x 20 mm

1430 mA

Table 1. Various high-ripple current rated capacitors and their ripple current ratings; see also Component Listings.

 

PI-2736-042301

Figure 1. Proper layout with consistent path lengths and trace widths (equal impedance) to four (4) output capacitors.