SLVSAO5B December 2010 – October 2015 TPS62590-Q1
PRODUCTION DATA.
- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Parameter Measurement Information
- 8 Detailed Description
- 9 Application and Implementation
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
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 TPS62590-Q1 device is a highly efficient, synchronous step-down, DC-DC converter with an adjustable output voltage and an output current of up to 1 A. The device can be used in buck converter applications with an input range from 2.5 V to 6 V. The TPS62590-Q1 device is optimized for space constrained applications and consumes 15-µA current (typ) in power-save mode.
9.2 Typical Application
Figure 20. TPS62590-Q1DRV Adjustable 1.8 V
Figure 21. TPS62590-Q1DRV Adjustable 3.3 V
9.2.1 Design Requirements
The input voltage for this device must be from 2.5 V to 6 V. The output voltage must be set using an external voltage divider. The internal compensation network of the device is optimized for an LC output filter that is composed of a 2.2-μH inductor and a 10-μF ceramic capacitor with a external feed-forward capacitor of 22 pF. The Recommended Operating Conditions table specifies the allowed range for input voltages, output voltages, output current, output inductor and output buffer capacitor. The values listed in this table must be followed when designing the regulator. Low-ESR ceramic capacitors should be used at the input and output for better filtering and ripple performance. The Detailed Design Procedure section provides the necessary equations and guidelines for selecting external components for this regulator.
9.2.2 Detailed Design Procedure
Table 2 lists the recommended components for the circuit shown in Parameter Measurement Information.
Table 2. List of Components
| COMPONENT REFERENCE | PART NUMBER | MANUFACTURER | VALUE |
|---|---|---|---|
| CIN | GRM188R60J106M | Murata | 10-μF, 6.3-V. X5R ceramic |
| COUT | GRM188R60J106M | Murata | 10-μF, 6.3-V. X5R ceramic |
| C1 | Murata | 22-pF, ceramic | |
| L1 | LPS3015 | Coilcraft | 2.2 μH, 110 mΩ |
| R1, R2 | Values depending on the programmed output voltage | ||
9.2.2.1 Output Voltage Setting
The output voltage can be calculated to:
where
- internal reference voltage VREF = 0.6 V typically
To minimize the current through the feedback divider network, R2 should be 180 kΩ or 360 kΩ. The sum of R1 and R2 should not exceed approximately 1 MΩ, to keep the network robust against noise.
9.2.2.2 External Feed-Forward Capacitor
An external feedforward capacitor C1 is required for optimum load-transient response. The value of C1 should be in the range between 22 pF and 33 pF.
9.2.2.3 Output Filter Design (Inductor and Output Capacitor)
The Recommended Operating Conditions table lists the allowed range of inductor and capacitor. For stable operation, L and C values of the output filter should not fall below 1-µH effective inductance and 3.5-µF effective capacitance.
9.2.2.3.1 Inductor Selection
The inductor value has a direct effect on the ripple current. The selected inductor must be rated for its DC resistance and saturation current. The inductor ripple current (ΔIL) decreases with higher inductance and increases with higher VI or VO.
The inductor selection also impacts the output-voltage ripple in PFM mode. Higher inductor values lead to lower output-voltage ripple and higher PFM frequency; lower inductor values lead to a higher output-voltage ripple but lower PFM frequency.
Equation 3 calculates the maximum inductor current under static load conditions. The saturation current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 4. This is recommended because during heavy load transients the inductor current rises above the calculated value.
where
- f = Switching frequency (2.25 MHz, typical)
- L = Inductor Value
- ΔIL = Peak-to-peak inductor ripple current
- ILmax = Maximum inductor current
A more conservative approach is to select the inductor current rating just for the maximum switch current of the corresponding converter.
Accepting larger values of ripple current allows the use of low inductance values, but results in higher output voltage ripple, greater core losses, and lower output-current capability.
The total losses of the coil have a strong impact on the efficiency of the dc/dc conversion and consist of both the losses in the dc resistance (R(DC)) and the following frequency-dependent components:
- The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)
- Additional losses in the conductor from the skin effect (current displacement at high frequencies)
- Magnetic field losses of the neighboring windings (proximity effect)
- Radiation losses
9.2.2.3.2 Output Capacitor Selection
The advanced fast-response voltage-mode control scheme of the TPS62590-Q1 allows the use of tiny ceramic capacitors. Ceramic capacitors with low ESR values have the lowest output-voltage ripple and are recommended. The output capacitor requires either an X7R or X5R dielectric. Y5V and Z5U dielectric capacitors, aside from their wide variation in capacitance over temperature, become resistive at high frequencies.
At nominal load current, the device operates in PWM mode, and the RMS ripple current is calculated as:
The overall output voltage ripple under the same conditions is the sum of the voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and discharging the output capacitor:
At light load currents, the converter operates in power-save mode, and the output-voltage ripple is dependent on the output capacitor and inductor values. Larger output capacitor and inductor values minimize the voltage ripple in PFM mode and tighten dc output accuracy in PFM mode.
9.2.2.3.3 Input Capacitor Selection
The buck converter has a natural pulsating input current; therefore, a low ESR input capacitor is required for best input voltage filtering and minimizing the interference with other circuits caused by high input voltage spikes. For most applications, a 10-μF ceramic capacitor is recommended. The input capacitor can be increased without any limit for better input voltage filtering.
Take care when using only small ceramic input capacitors. When a ceramic capacitor is used at the input and the power is being supplied through long wires, such as from a wall adapter, a load step at the output or VIN step on the input can induce ringing at the VIN pin. The ringing can couple to the output and be mistaken as loop instability or could even damage the part by exceeding the maximum ratings.
9.2.3 Application Curves
