TK65130MTL/30M データシートの表示（PDF） - Toko America Inc

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TK65130MTL/30M

STEP-UP VOLTAGE CONVERTER WITH VOLTAGE MONITOR

Toko America Inc  

TK651xx

PULSED LOAD APPLICATION

Often in the world of power conversion, the current draw of the load circuit is not constant, but rather pulsed. It is common

in power supply design to size the power path large enough, and make the feedback loop fast enough to support these

pulsed maximum currents. For applications where the pulse width is long or unpredictable, this approach may be

warranted. However, in applications where the pulse width and maximum frequency of occurrence is predictable, such

as digital cell phones or two-way pagers, it may be easier and wiser to increase the energy storage in the output filter

of the power supply and keep the power path small. This leads to the need for a very large value output capacitor.

Panasonic makes a series AL gold cap “super cap” which is a low voltage, large value capacitor in the one farad range.

Before designing a low power DC-DC converter with a “super cap” in its output filter, it is necessary to know the loading

profile (the waveform of the current going into the load from the output of the converter) of the application in which it is

to be used. The converter can then be designed so that the “super cap” can be recharged in the time before the next big

discharge current pulse comes along.

Figure 5 is an example “super cap” charge/discharge diagram showing that the charge into the cap needs to equal the

charge leaving the cap during discharge. This diagram comes from the loading and unloading profile information. In

reality, some extra charge needs to go into the cap to make up for the losses caused by ESR of the cap.

1A

60 ms

Note: Equal charge into and out of “supercap”

2 s (30 mA) = 60 ms (1A)

Drawing not to scale

IOUT

30 mA

2s

time

FIGURE 5: “SUPER CAP” CHARGE/DISCHARGE DIAGRAM

Figure 6 is a schematic for this “super cap” example application.

IB

VIN

RN

1k

CN

10 µF

L = 39 µF

VIN

GND

IND

D

CS

220 pF

RS

1k

LOI

GND

VOUT

-

CD

+ 10 µF

IOUT

+

"SUPERCAP"

1F

GOLD CAP

VOUT

FIGURE 6: PULSED LOAD “SUPER CAP” APPLICATION SCHEMATIC

January 1999 TOKO, Inc.

Page 19

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