SLVSD89B November 2016 – November 2017 TLV62568
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The following section discusses the design of the external components to complete the power supply design for several input and output voltage options by using typical applications as a reference.
For this design example, use the parameters listed in Table 2 as the input parameters.
|DESIGN PARAMETER||EXAMPLE VALUE|
|Input voltage||2.5 V to 5.5 V|
|Output voltage||1.8 V|
|Maximum output current||1.0 A|
Table 3 lists the components used for the example.
|C1||4.7 µF, Ceramic Capacitor, 10 V, X7R, size 0805, GRM21BR71A475KA73L||Murata|
|C2||10 µF, Ceramic Capacitor, 10 V, X7R, size 0805, GRM21BR71A106KE51L||Murata|
|L1||2.2 µH, Power Inductor, SDER041H-2R2MS||Cyntec|
|R1,R2,R3||Chip resistor,1%,size 0603||Std.|
|C3||Optional, 6.8 pF if it is needed||Std.|
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An external resistor divider is used to set output voltage according to Equation 2.
When sizing R2, in order to achieve low current consumption and acceptable noise sensitivity, use a maximum of 200 kΩ for R2. Larger currents through R2 improve noise sensitivity and output voltage accuracy but increase current consumption.
A feed forward capacitor, C3 improves the loop bandwidth to make a fast transient response (shown in Figure 19). 6.8-pF capacitance is recommended for R2 of 100-kΩ resistance. A more detailed discussion on the optimization for stability vs. transient response can be found in SLVA289.
The inductor and output capacitor together provide a low-pass filter. To simplify this process, Table 4 outlines possible inductor and capacitor value combinations. Checked cells represent combinations that are proven for stability by simulation and lab test. Further combinations should be checked for each individual application.
|VOUT [V]||L [µH](1)||COUT [µF](2)|
|0.6 ≤ VOUT < 1.2||1||+|
|1.2 ≤ VOUT < 1.8||1||+||+|
|1.8 ≤ VOUT||1||+||+||+|
The main parameters for inductor selection is inductor value and then saturation current of the inductor. To calculate the maximum inductor current under static load conditions, Equation 3 is given:
It is recommended to choose a saturation current for the inductor that is approximately 20% to 30% higher than IL,MAX. In addition, DC resistance and size should also be taken into account when selecting an appropriate inductor.
The architecture of the TLV62568 allows use of tiny ceramic-type output capacitors with low equivalent series resistance (ESR). These capacitors provide low output voltage ripple and are thus recommended. To keep its resistance up to high frequencies and to achieve narrow capacitance variation with temperature, it is recommended to use X7R or X5R dielectric.
The input capacitor is the low impedance energy source for the converter that helps provide stable operation. A low ESR multilayer ceramic capacitor is recommended for best filtering. For most applications, 4.7-µF input capacitance is sufficient; a larger value reduces input voltage ripple.
The TLV62568 is designed to operate with an output capacitor of 10 µF to 47 µF, as outlined in Table 4.
VIN = 5 V, VOUT = 1.8 V, L = 2.2 μH, TA = 25°C, unless otherwise noted.
|VIN = 5 V|
|VIN = 5 V|
|IOUT = 0.5 A|
|IOUT = 1 A|
|Load Step 0.3 A to 1 A, 1A/µs slew rate|
|VOUT = 1.8 V|
|IOUT = 0.5 A|
|IOUT = 0.1 A|
|IOUT = 0.1 A|
|Load Step 0.3 A to 1 A, 1A/µs slew rate||C3 = 6.8 pF|