A tantalum polymer capacitor is one constructed with a tantalum

(Ta) anode, a tantalum pentoxide (Ta

) dielectric, and a solid

polymer electrolyte. This construction method offers a variety

of advantages, including high temperature ratings and stability

over temperature, voltage, and time. These characteristics allow

tantalum polymer capacitors to meet, and exceed, AEC-Q200

automotive standard requirements. KEMET’s tantalum polymer

capacitors (KO-CAP (TM) series) offer low ESR to minimize

power losses and unwanted noise, and can withstand the high

temperatures of automotive applications. Specically, the T599

tantalum polymer capacitor has excellent characteristics all the

way up to 150°C, offering an ultra extended life expectancy.

(Ratings from KEMET series T599 at 100 kHz)

• Low max series resistance, from 25 mΩ to 150 mΩ

• Stable across temperatures, from -55°C to 150°C

• Ultra long life expectancy for high and ultra extended

mission proles

Automotive electronics are usually powered by a battery. DC/DC

converters are critical for automotive applications because they

step down the battery voltage, which is usually +12V DC, to a

more usable voltage rail for electronics — +5V, +3.3V, +1.8V, or

even lower. The conversions are often also done in stages, such

as 12V to 5V, and 5V to 3.3V. DC/DC converters create the volt-

age for these rails, and capacitors help those converters function

and provide stable, clean power.

For automotive applications utilizing the T599 series capacitors

for max temperatures up to 150°C, KEMET recommends derat-

ing the voltage according to the temperature, as follows:

The simplied schematic above shows what a DC/DC convert-

er used in an automotive application to step down a +5V rail

to a +3.3V rail would look like. In a DC/DC converter circuit,

capacitance is required at both the input and the output of the

converter. The input capacitor(s) (C1) ensures that instanta-

neous current is available to the converter while it is switching.

The output capacitor(s) (C2) ensures that instantaneous current

is available to the load (DSP, microprocessor, I/O, USB, etc)

while the converter is switching. Each of these capacitors, in

an automotive application, must not only be designed to meet

the capacitance needs of the circuit, but also selected to meet

the high temperatures and harsh conditions of the AEC-Q200

standard, and beyond.

INTRODUCTION

ADVANTAGES OF KEMET’S

T599 TANTALUM POLYMER

CAPACITORS

AUTOMOTIVE DC/DC

CONVERTER APPLICATION

EXAMPLE

VOLTAGE DERATING FOR HIGH

TEMPERATURES

Figure 1 – Simplied DC/DC converter schematic

Figure 2 – T599 (150ºC) Series - Temperature and Voltage Derating

Application Note for T599 Tantalum Polymer

Capacitors in Automotive Designs

Max Operational Temperature 150°C

Rated Voltage Derating Voltage

-55°C -- 105°C 105°C -- 150°C -55°C -- 105°C 105°C -- 125°C 125°C -- 150°C

2.5V 1.7V 2.3V 1.8V 1.5V

4V 2.7V 3.6V 2.9V 2.4V

6.3V 4.2V 5.7V 4.6V 3.8V

10V 6.7V 9V 7.2V 6V

16V 10.7V 12.8V 10.2V 8.6V

20V 13.4V 16V 12.8V 10.7V

25V 16.8V 20V 16V 13.4V

35V 23.5V 28V 22.4V 18.8V

50V 33.5V 40V 32V 26.8V

In the case of selecting the input capacitor (C1) for a DC/DC

converter in an automotive application, the DC/DC converter

needs to supply 3.3V. Let’s assume this regulator is designed for

the following conditions:

OUT

= 3.3V

= 5V

Efciency (╖) = 85% (from efciency curves in DC/DC

or module datasheet)

Output transient current (ΔI

OUT

) = 1.0A

Using this information, the input transient expected can be

calculated as follows:

For our example,

Next, we must determine the series inductance. If the circuit

does not include a series lter inductor, the stray inductance

introduced by the PCB layout will be the only inductance. If a

series lter inductor is used, that inductance value can be added

to the inductance introduced by the layout.

Stray microstrip layout inductance can be calculated using the

following equation:

For our example, we will assume that the layout is such that

the stray inductance is 50 nH, and a required lter inductor of

220 nH is used. Effective PCB layout guidelines are important

because the stray inductance has a direct effect on the value of

bulk capacitance required, as we will see shortly.

Next, a design decision must be made regarding how much volt-

age variation is permissible on the input voltage bulk capacitor.

For this example, we will assume that

With that, the minimum required bulk capacitance is given by the

following equation:

where I

is the input transient current.

For our example,

This is the absolute minimum bulk capacitance required. Look-

ing at the KEMET T599 datasheet, the closest value above 20

µF with a rating above 10V (15V / 50% derating) is part number

T599B336M010ATE070. This part has a capacitance of 33µF

and is rated at 10V.

SIZING THE CAPACITOR

Figure 3 – T599 (150ºC) Series – Temperature and Voltage Derating