0402, 6.3V, X5R

0603, 10V, X5R

0

1.0

2.0

3.0

4.0

5.0

DC BIAS (V)

20

40

60

80

100

LM10502

www.ti.com

SNVS884B – AUGUST 2012 – REVISED MAY 2013

Table 2. Recommended Inductors

Value

Manufacturer

Part Number

DCR

Current

Package

2.2 µH

Murata

LQH55PN2R2NR0L

31 m

Ω

2.5A

2220

2.2 µH

TDK

NLC565050T-2R2K-PF

60 m

Ω

1.3A

2220

2.2 µH

Murata

LQM2MPN2R2NG0

110 m

Ω

1.2A

806

OUTPUT AND INPUT CAPACITORS CHARACTERISTICS

Special attention should be paid when selecting these components. As shown in the following figure, the DC bias

of these capacitors can result in a capacitance value that falls below the minimum value given in the

recommended capacitor specifications table. Note that the graph shows the capacitance out of spec for the 0402

case size capacitor at higher bias voltages. It is therefore recommended that the capacitor manufacturers’

specifications for the nominal value capacitor are consulted for all conditions, as some capacitor sizes (e.g.,

0402) may not be suitable in the actual application.

Figure 24. Typical Variation in Capacitance vs.

DC Bias

The ceramic capacitor’s capacitance can vary with temperature. The capacitor type X7R, which operates over a

temperature range of

−55°C to +125°C, will only vary the capacitance to within ±15%. The capacitor type X5R

has a similar tolerance over a reduced temperature range of

−55°C to +85°C. Many large value ceramic

capacitors, larger than 1µF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance

can drop by more than 50% as the temperature varies from 25°C to 85°C. Therefore X7R is recommended over

Z5U and Y5V in applications where the ambient temperature will change significantly above or below 25°C.

Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more

expensive when comparing equivalent capacitance and voltage ratings in the 0.47 µF to 44 µF range. Another

important consideration is that tantalum capacitors have higher ESR values than equivalent size ceramics. This

means that while it may be possible to find a tantalum capacitor with an ESR value within the stable range, it

would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the

same ESR value. It should also be noted that the ESR of a typical tantalum will increase about 2:1 as the

temperature goes from 25°C down to

−40°C, so some guard band must be allowed.

Output Capacitor Selection

The output capacitor of a switching converter absorbs the AC ripple current from the inductor and provides the

initial response to a load transient. The ripple voltage at the output of the converter is the product of the ripple

current flowing through the output capacitor and the impedance of the capacitor. The impedance of the capacitor

can be dominated by capacitive, resistive, or inductive elements within the capacitor, depending on the frequency

of the ripple current. Ceramic capacitors have very low ESR and remain capacitive up to high frequencies. Their

inductive component can usually be neglected at the frequency ranges at which the switcher operates.

Copyright © 2012–2013, Texas Instruments Incorporated

Submit Documentation Feedback

25

Product Folder Links: LM10502