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ZHCS442F September 2011 – November 2016 TPS62080 , TPS62080A , TPS62081 , TPS62082

PRODUCTION DATA.

9 Application and Implementation

NOTE

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.

9.1 Application Information

The TPS62080 and TPS62080A are synchronous step-down converter whose output voltage is adjusted by component selection. 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. The TPS62081 and TPS62082 provide a fixed output volage which do not need an external resistor divider.

9.2 Typical Application

TPS62080 TPS62080A TPS62081 TPS62082 TPS62080_adj_typ_app.gif

Figure 7. Typical Application Schematic

9.2.1 Design Requirements

For this design example, use Table 2 as the input parameters.

Table 2. Design Parameters

DESIGN PARAMETER	EXAMPLE VALUE
Input voltage	2.3 V to 6 V
Output voltage	1.2 V
Output ripple voltage	< 20 mV
Maximum output current	1.2 A

9.2.2 Detailed Design Procedure

Table 3 lists the components used for the example.

Table 3. List of Components

REFERENCE	DESCRIPTION	MANUFACTURER
C1	10 uF, Ceramic Capacitor, 6.3 V, X5R, size 0603	Std
C2	22 uF, Ceramic Capacitor, 6.3 V, X5R, size 0805, GRM21BR60J226ME39L	Murata
L1	1.0 µH, Power Inductor, 2.2 A, size 3 × 3 × 1.2 mm, XFL3012-102MEB	Coilcraft
R1	Depending on the output voltage of TPS62080, 1%; Not populated for TPS62081, TPS62082;	Std
R2	39.2k, Chip Resistor, 1/16W, 1%, size 0603	Std
R3	178k, Chip Resistor, 1/16W, 1%, size 0603	Std

9.2.2.1 Setting the Output Voltage

The TPS608x devices are available as fixed and adjustable output voltage versions. The fixed voltage versions are internally programmed to a fixed output voltage, whereas the adjustable output voltage version needs to be programmed via an external voltage divider to set the desired output voltage.

9.2.2.1.1 Adjustable Output Voltage Version

For the adjustable output voltage version, an external resistor divider is used. By selecting R₁ and R₂, the output voltage is programmed to the desired value.

When the output voltage is regulated, the typical voltage at the FB pin is V_FB for the adjustable devices. The following equation can be used to calculate R₁ and R₂.

Equation 2. TPS62080 TPS62080A TPS62081 TPS62082 EQ1_VS_lvsae8.gif

For best accuracy, R2 should be kept smaller than 40kΩ to ensure that the current flowing through R2 is at least 100 times larger than I_FB. Changing towards a lower value increases the robustness against noise injection. Changing towards higher values reduces the input current. For lowest input current during Snooze Mode, it is recommended to use a fixed output voltage version such as TPS62081 and TPS62082.

9.2.2.2 Output Filter Design

The inductor and the output capacitor together provide a low pass filter. To simplify this process, Table 4 outlines possible inductor and capacitor value combinations for most applications. Checked cells represent combinations that are proven for stability by simulation and lab test. Further combinations should be checked for each individual application.

Table 4. Matrix of Output Capacitor and Inductor Combinations

L [µH]⁽³⁾	C_OUT [µF]⁽³⁾
L [µH]⁽³⁾	10	22	47	100	150
0.47
1	+	+⁽¹⁾⁽²⁾	+	+
2.2	+	+	+	+
4.7

(1) Plus mark indicates recommended filter combinations.

(2) Filter combination in typical application.

(3) Capacitance tolerance and bias voltage de-rating is anticipated. The effective capacitance can vary by +20% and –50%. Inductor tolerance and current de-rating is anticipated. The effective inductance can vary by +20% and –30%.

9.2.2.3 Inductor Selection

The main parameters for the inductor selection are the inductor value and then the saturation current of the inductor. To calculate the maximum inductor current under static load conditions, Equation 3 is given.

Equation 3. TPS62080 TPS62080A TPS62081 TPS62082 Eq_IL_peak_PWM_lvsae8.gif

where

I_OUT,MAX = Maximum output current
ΔI_L = Inductor current ripple
f_SW = Switching frequency
L = Inductor value

TI recommends to choose the saturation current for the inductor 20%~30% higher than the I_L,MAX, out of Equation 3. A higher inductor value is also useful to lower ripple current, but increases the transient response time as well. The following inductors are recommended for use.

Table 5. List of Recommended Inductors

INDUCTANCE [µH]	CURRENT RATING [mA]	DIMENSIONS L x W x H [mm³]	DC RESISTANCE [mΩ typ]	TYPE	MANUFACTURER
1.0	2500	3 x 3 x 1.2	35	XFL3012-102ME	Coilcraft
1.0	1650	3 x 3 x 1.2	40	LQH3NPN1R0NJ0	Murata
2.2	2500	4 x 3.7 x 1.65	49	LQH44PN2R2MP0	Murata
2.2	1600	3 x 3 x 1.2	81	XFL3012-222ME	Coilcraft

9.2.2.4 Capacitor Selection

The input capacitor is the low impedance energy source for the converter which helps to provide stable operation. A low ESR multilayer ceramic capacitor is recommended for best filtering and should be placed between VIN and GND as close as possible to those pins. For most applications 10 μF is sufficient, though a larger value reduces input current ripple.

The architecture of the TPS6208X allows the use of tiny ceramic output capacitors with low equivalent series resistance (ESR). These capacitors provide low output voltage ripple and are recommended. To keep its resistance up to high frequencies and to get narrow capacitance variation with temperature, it's recommended to use X7R or X5R dielectric. The TPS6208x is designed to operate with an output capacitance of 10 µF to 100 µF and beyond, as outlined in Table 4. Load transient testing and measuring the bode plot are good ways to verify stability with larger capacitor values.