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ZHCSH71A September 2017 – December 2017 TPS62097-Q1

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8 Application Information

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.

8.1 Application Information

The following section discusses the design of the external components to complete the power supply design of the TPS62097-Q1.

8.2 1.8-V Output Application

Figure 6. 1.8-V Output Application Schematic

8.2.1 Design Requirements

For this design example, use the following as the input parameters.

Table 3. Design Parameters

DESIGN PARAMETER	EXAMPLE VALUE
Input voltage range	2.5 V to 6 V
Output voltage	1.8 V
Output current	2.0 A

Table 4 lists the components used for the example.

Table 4. List of Components

REFERENCE	DESCRIPTION	MANUFACTURER⁽¹⁾
C1	10 μF, Ceramic Capacitor, 6.3V, X7R, size 0805, C2012X7R0J106M125AB	TDK
C2	22 μF, Ceramic Capacitor, 6.3V, X7S, size 0805, C2012X7S1A226M125AC	TDK
C3	10 nF, Ceramic Capacitor, 6.3V, X7R, size 0603, GRM188R70J103KA01	Murata
L1	1 µH, Shielded, 5.4A, XFL4020-102MEB	Coilcraft
R1	Depending on the output voltage, 1% accuracy	Std
R2	20 kΩ, 1% accuracy	Std
R3	100 kΩ, 1% accuracy	Std

(1) See Third-party Products Disclaimer

8.2.2 Detailed Design Procedure

8.2.2.1 Setting the Output Voltage

The output voltage is set by an external resistor divider according to the following equation:

Equation 4. TPS62097-Q1 EQ2_vout_lvsaw2.gif

R2 should not be higher than 20 kΩ to reduce noise coupling into the FB pin and improve the output voltage regulation. Choose additional resistor values for other outputs. A feed forward capacitor is not required.

The fixed output voltage version, TPS6209733-Q1, does not need an external resistor divider. TI recommends to connect the FB pin to AGND for improved thermal performance.

8.2.2.2 Output Filter Design

The inductor and the output capacitor together provide a low-pass filter. To simplify the selection process, Table 5 outlines possible inductor and capacitor value combinations for most applications.

Table 5. Output Capacitor / Inductor Combinations

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

(1) Typical application configuration. Other '+' mark indicates recommended filter combinations. Other values may be acceptable in applications but should be fully tested by the user. Refer to the application note SLVA710.

(2) Inductor tolerance and current de-rating is anticipated. The effective inductance can vary by +20% and -30%. The required effective inductance is 500nH minimum.

(3) Capacitance tolerance and bias voltage de-rating is anticipated. The effective capacitance can vary by 20% and -50%.

8.2.2.3 Inductor Selection

The main parameters for the inductor selection are the inductor value and the saturation current. To calculate the maximum inductor current under static load conditions, Equation 5 is given.

Equation 5. TPS62097-Q1 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% to 30% higher than the I_L,MAX, out of Equation 5. A higher inductor value is also useful to lower ripple current but increases the transient response time as well.

8.2.2.4 Capacitor Selection

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

The architecture of the TPS62097-Q1 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 low resistance up to high frequencies and to get narrow capacitance variation with temperature, TI recommends to use X7R or X5R dielectrics. The recommended typical output capacitor value is 22 μF and can vary over a wide range as outlined in Table 5.

Ceramic capacitors have a DC-Bias effect, which has a strong influence on the final effective capacitance. Choose the right capacitor carefully in combination with considering its package size and voltage rating. Ensure that the input effective capacitance is at least 5 μF and the output effective capacitance is at least 10 μF.