SLVSAC4B November   2010  – December 2015 TLV62065

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Mode Selection
      2. 7.3.2 Enable
      3. 7.3.3 Undervoltage Lockout
      4. 7.3.4 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Soft-Start
      2. 7.4.2 Power-Save Mode
        1. 7.4.2.1 100% Duty Cycle Low Dropout Operation
      3. 7.4.3 Internal Current Limit / Fold-back Current Limit for Short-Circuit Protection
      4. 7.4.4 Output Capacitor Discharge
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Output Voltage Setting
        2. 8.2.2.2 Output Filter Design (Inductor and Output Capacitor)
          1. 8.2.2.2.1 Inductor Selection
          2. 8.2.2.2.2 Output Capacitor Selection
          3. 8.2.2.2.3 Input Capacitor Selection
        3. 8.2.2.3 Checking Loop Stability
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8 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.

8.1 Application Information

The TLV62065 is a high-efficiency synchronous step-down DC/DC converter providing up to 2-A output current.

8.2 Typical Application

TLV62065 typ_app1_18adj_lvsac4.gif Figure 8. TLV62065 1.8-V Adjustable Output Voltage Configuration

8.2.1 Design Requirements

The device operates over an input voltage range from 2.9 V to 5.5 V. The output voltage is adjustable using an external feedback divider.

8.2.2 Detailed Design Procedure

8.2.2.1 Output Voltage Setting

The output voltage can be calculated by Equation 2 with an internal reference voltage VREF typically 0.6 V.

Equation 2. TLV62065 inl1_vout_lvs833.gif

To minimize the current through the feedback divider network, R2 should be within the range of 120 kΩ to 360 kΩ. The sum of R1 and R2 should not exceed approximately 1 MΩ, to keep the network robust against noise. An external feed-forward capacitor Cff is required for optimum regulation performance. Lower resistor values can be used. R1 and Cff places a zero in the loop. The right value for Cff can be calculated by Equation 3 and Equation 4:

Equation 3. TLV62065 EQ2_fz1_lvs833.gif
Equation 4. TLV62065 EQ3_cff1_lvs833.gif

8.2.2.2 Output Filter Design (Inductor and Output Capacitor)

The internal compensation network of TLV62065 is optimized for a LC output filter with a corner frequency of:

The device operates with nominal inductors of 1.0 µH to 1.2 µH and with 10 µF to 22 µF small X5R and X7R ceramic capacitors. Please refer to the lists of inductors and capacitors. The device is optimized for a 1-µH inductor and 10-µF output capacitor.

8.2.2.2.1 Inductor Selection

The inductor value has a direct effect on the ripple current. The selected inductor has to 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.

Equation 5 calculates the maximum inductor current in PWM mode under static load conditions. The saturation current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 6. This is recommended because during heavy load transient the inductor current rises above the calculated value.

Equation 5. TLV62065 q3_delta_lvs833_.gif
Equation 6. TLV62065 q4_ilmax_lvs833.gif

where

  • f = Switching frequency (3 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 switch current limit ILIMF of the converter.

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

Table 1. List of Inductors

DIMENSIONS [mm3] INDUCTANCE μH INDUCTOR TYPE SUPPLIER
3.2 x 2.5 x 1.0 max 1.0 LQM32PN (MLCC) Murata
3.7 x 4 x 1.8 max 1.0 LQH44 (wire wound) Murata
4.0 x 4.0 x 2.6 max 1.2 NRG4026T (wire wound) Taiyo Yuden
3.5 x 3.7 x 1.8 max 1.2 DE3518 (wire wound) TOKO

8.2.2.2.2 Output Capacitor Selection

The advanced fast-response voltage mode control scheme of the TLV62065 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 and may not be used. For most applications a nominal 10-µF or 22-µF capacitor is suitable. At small ceramic capacitors, the DC-bias effect decreases the effective capacitance. Therefore a 22-µF capacitor can be used for output voltages higher than 2 V, see list of capacitors.

In case additional ceramic capacitors in the supplied system are connected to the output of the DC–DC converter, the output capacitor COUT need to be decreased in order not to exceed the recommended effective capacitance range. In this case a loop stability analysis must be performed as described later.

At nominal load current, the device operates in PWM mode and the RMS ripple current is calculated by Equation 7:

Equation 7. TLV62065 q5_irmsc_lvs833.gif

8.2.2.2.3 Input Capacitor Selection

Because of the nature of the buck converter having a pulsating input current, 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. This ringing can couple to the output and be mistaken as loop instability or could even damage the part by exceeding the maximum ratings.

Table 2. List of Capacitors

CAPACITANCE TYPE SIZE [ mm3] SUPPLIER
10 μF GRM188R60J106M 0603: 1.6 x 0.8 x 0.8 Murata
22 μF GRM188R60G226M 0603: 1.6 x 0.8 x 0.8 Murata
22 µF CL10A226MQ8NRNC 0603: 1.6 x 0.8 x 0.8 Samsung
10 µF CL10A106MQ8NRNC 0603: 1.6 x 0.8 x 0.8 Samsung

8.2.2.3 Checking Loop Stability

The first step of circuit and stability evaluation is to look from a steady-state perspective at the following signal:

  • Switching node, SW
  • Inductor current, IL
  • Output ripple voltage, VOUT(AC)

These are the basic signals that need to be measured when evaluating a switching converter. When the switching waveform shows large duty cycle jitter or the output voltage or inductor current shows oscillations, the regulation loop may be unstable. This is often a result of board layout and/or wrong L-C output filter combinations. As a next step in the evaluation of the regulation loop, the load transient response is tested. The time between the application of the load transient and the turn on of the P-channel MOSFET, the output capacitor must supply all of the current required by the load. VOUT immediately shifts by an amount equal to ΔI(LOAD) x ESR, where ESR is the effective series resistance of COUT. ΔI(LOAD) begins to charge or discharge COUT generating a feedback error signal used by the regulator to return VOUT to its steady-state value. The results are most easily interpreted when the device operates in PWM mode at medium to high load currents.

During this recovery time, VOUT can be monitored for settling time, overshoot, or ringing; that helps evaluate stability of the converter. Without any ringing, the loop has usually more than 45° of phase margin.

8.2.3 Application Curves

TLV62065 eff12_auto_lvs833.gif
VOUT = 1.2 V
Figure 9. Auto PFM/PWM Mode,
Linear Scale
TLV62065 eff33_auto_lvs833.gif
VOUT = 3.3 V
Figure 11. Auto PFM/PWM Mode,
Linear Scale
TLV62065 voacc_auto_lvs833.gif
i.
Figure 13. Auto PFM/PWM Mode
TLV62065 tc_pwm36_lvs833.gif
Figure 15. Typical Operation (PWM Mode)
TLV62065 load_tr_pwm_lvs833.gif
Figure 17. Load Transient Response
PWM Mode 0.2 A to 1A
TLV62065 load_tr_pfm200_lvs833.gif
Figure 19. Load Transient Response
200 mA to 1500 mA
TLV62065 line_tr_pfm_lvs833.gif
Figure 21. Line Transient PFM Mode
TLV62065 out_disc_lvs833.gif
Figure 23. Output Discharge
TLV62065 eff18_auto_lvs833.gif
VOUT = 1.8 V
Figure 10. Auto PFM/PWM Mode,
Linear Scale
TLV62065 eff18_for_lvs833.gif
Figure 12. Auto PFM/PWM Mode vs Forced PWM Mode,
Logarithmic Scale
TLV62065 voacc_for_lvs833.gif
Figure 14. Forced PWM Mode
TLV62065 tc_pfm36_lvs833.gif
Figure 16. Typical Operation (PFM Mode)
TLV62065 load_tr_pfm20_lvs833.gif
i.
Figure 18. Load Transient
PFM Mode 20 mA to 250 mA
TLV62065 line_tr_pwm_lvs833.gif
Figure 20. Line Transient Response PWM Mode
TLV62065 stup_18_lvs833.gif
Figure 22. Startup Into Load – VOUT 1.8 V