SLVSAQ5E March   2012  – May 2017 TPS62125


  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 Undervoltage Lockout
      2. 7.3.2 Enable Comparator (EN / EN_hys)
      3. 7.3.3 Power Good Output and Output Discharge (PG)
      4. 7.3.4 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Pulse Width Modulation (PWM) Operation
      2. 7.4.2 Power-Save Mode
      3. 7.4.3 100% Duty Cycle Low Dropout Operation
      4. 7.4.4 Soft-Start
      5. 7.4.5 Short-Circuit Protection
  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. Output Voltage Setting
        2. Enable Threshold and Hysteresis Setting
        3. Power Good (PG) Pullup and Output Discharge Resistor
        4. Output Filter Design (Inductor and Output Capacitor)
        5. Inductor Selection
        6. Output Capacitor Selection
        7. Input Capacitor Selection
      3. 8.2.3 Application Curves
    3. 8.3 System Examples
      1. 8.3.1 TPS62125 5-V Output Voltage Configuration
      2. 8.3.2 TPS62125 5-V VOUT
      3. 8.3.3 TPS62125 Operation From a Storage Capacitor Charged From a 0.5 mA Current Source
      4. 8.3.4 5 V to -5 V Inverter Configuration
  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 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Application and Implementation


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.

Application Information

The TPS62125 is a high-efficiency synchronous step-down converter providing a wide output voltage range from 1.2 V to 10 V.

Typical Application

TPS62125 TPS62125_app_3.3V.gif Figure 8. TPS62125 3.3-V Output Voltage Configuration

Design Requirements

The device operates over an input voltage range from 3 V to 17 V. The output voltage is adjustable using an external feedback divider.

Detailed Design Procedure

Output Voltage Setting

The output voltage can be calculated by:

Equation 5. TPS62125 EQ_VOUT_setting.gif

The internal reference voltage for the error amplifier, VREF_FB, is nominal 0.808 V. However for the feedback resistor divider selection, it is recommended to use the value 0.800 V as the reference. Using this value, the output voltage sets 1% higher and provides more headroom for load transients as well for line and load regulation. The current through the feedback resistors R1 and R2 should be higher than 1 µA. In applications operating over full temperature range or in noisy environments, this current may be increased for robust operation. However, higher currents through the feedback resistors impact the light load efficiency of the converter.

Table 1 shows a selection of suggested values for the feedback divider network for most common output voltages.

Table 1. Suggested Values for Feedback Divider Network

OUTPUT VOLTAGE 1.2 V 1.8 V 3.3 V 5 V 6.7 V 8 V
R1 [kΩ] 180 300 1800 1100 1475 1800
R2 [kΩ] 360 240 576 210 200 200

Enable Threshold and Hysteresis Setting

TPS62125 programmable_UVLO.gif Figure 9. Using the Enable Comparator Threshold and Hysteresis for an Input SVS (Supply Voltage Supervisor)

The enable comparator can be used as an adjustable input supply voltage supervisor (SVS) to start and stop the DC/DC converter depending on the input voltage level. The input voltage level, VIN_startup, at which the device starts up is set by the resistors REN1 and REN2 and can be calculated by :

Equation 6. TPS62125 EQ_VENTH_rising.gif

The resistor values REN1 and REN2 can be calculated by:

Equation 7. TPS62125 EQ_REN1.gif
Equation 8. TPS62125 EQ_REN2.gif

The input voltage level VIN_stop at which the device will stop operation is set by REN1, REN2 and REN HYS and can be calculated by:

Equation 9. TPS62125 EQ_VENTH_falling.gif

The resistor value REN_hys can be calculated according to:

Equation 10. TPS62125 EQ_REN_hys.gif

The current through the resistors REN1, REN2, and REN HYS should be higher than 1 µA. In applications operating over the full temperature range and in noisy environments, the resistor values can be reduced to smaller values.

TPS62125 EN_comp_graphic1.gif Figure 10. Using the EN Comparator as Input SVS for Proper VOUT Ramp Up

Power Good (PG) Pullup and Output Discharge Resistor

The power good open collector output needs an external pull up resistor to indicate a high level. The pull up resistor can be connected to a voltage level up to 10 V. The output can sink current up to 0.4 mA with specified output low level of less than 0.3 V. The lowest value for the pull up resistor can be calculated by:

Equation 11. TPS62125 EQ_Pullup_VOmaxL.gif
TPS62125 pg_output.gif Figure 11. PG Open Collector Output

The PG pin can be used to discharge the output capacitor. The PG output has an internal resistance RIPG of typical 600 Ω and minimum 400 Ω. The maximum sink current into the PG pin is 10 mA. In order to limit the discharge current to the maximum allowable sink current into the PG pin, the external pull up resistor RPull up can be calculated to:

Equation 12. TPS62125 EQ_Pullup_discharge_min.gif

In case a negative value is calculated, the external pull up resistor can be removed and the PG pin can be directly connected to the output.

Output Filter Design (Inductor and Output Capacitor)

The external components have to fulfill the needs of the application, but also the stability criteria of the devices control loop. The TPS62125 is optimized to work within a range of L and C combinations. The LC output filter inductance and capacitance have to be considered together, creating a double pole, responsible for the corner frequency of the converter. Table 2 can be used to simplify the output filter component selection.

Table 2. Recommended LC Output Filter Combinations

10 µF 2 x 10 µF 22 µF 47 µF
VOUT 1.2 V - 1.8 V
22 (3)
VOUT 1.8 V - 3.3 V
15 (3)
22 (3)
VOUT 3.3 V - 5 V
15 (3) (3)
VOUT 5 V - 10 V
10 (3) (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%.
This LC combination is the standard value and recommended for most applications.

More detailed information on further LC combinations can be found in application note SLVA515.

Inductor Selection

The inductor value affects its peak-to-peak ripple current, the PWM-to-PFM transition point, the output voltage ripple and the efficiency. 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 VIN or VOUT and can be estimated according to Equation 13.

Equation 14 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 14. This is recommended because during heavy load transient the inductor current will rise above the calculated value. A more conservative way is to select the inductor saturation current according to the high-side MOSFET switch current limit ILIMF.

Equation 13. TPS62125 EQ8_IDIL_lvsad5.gif
Equation 14. TPS62125 EQ9_ILmax_lvsad5.gif


  • TON: See Equation 1
  • L: Inductance
  • ΔIL: Peak to Peak inductor ripple current
  • ILmax: Maximum Inductor current

In DC/DC converter applications, the efficiency is essentially affected by the inductor AC resistance (i.e. quality factor) and by the inductor DCR value. To achieve high-efficiency operation, take care in selecting inductors featuring a quality factor above 25 at the switching frequency. Increasing the inductor value produces lower RMS currents, but degrades transient response. For a given physical inductor size, increased inductance usually results in an inductor with lower saturation current.

The total losses of the coil consist of both the losses in the DC resistance (RDC) 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

The following inductor series from different suppliers have been used with the TPS62125.

Table 3. List of Inductors

10 / 15 0.33 max / 0.44 max. 3.3 x 3.3 x 1.4 LPS3314 Coilcraft
22 0.36 max. 3.9 x 3.9 x 1.8 LPS4018 Coilcraft
15 0.33 max. 3.0 x 2.5 x 1.5 VLF302515 TDK
10/15 0.44 max / 0.7 max. 3.0 x 3.0 x 1.5 LPS3015 Coilcraft
10 0.38 typ. 3.2 × 2.5 × 1.7 LQH32PN Murata

Output Capacitor Selection

Ceramic capacitors with low ESR values provide 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 light load currents the converter operates in power-save mode and the output voltage ripple is dependent on the output capacitor value and the PFM peak inductor current. Higher output capacitor values minimize the voltage ripple in PFM Mode and tighten DC output accuracy in PFM mode. In order to achieve specified regulation performance and low-output voltage ripple, the DC-bias characteristic of ceramic capacitors must be considered. The effective capacitance of ceramic capacitors drops with increasing DC-bias voltage. Due to this effect, it is recommended for output voltages above 3.3 V to use at least 1 x 22-µF or 2 x 10-µF ceramic capacitors on the output.

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 voltage rating and DC bias characteristic of ceramic capacitors need to be considered. The input capacitor can be increased without any limit for better input voltage filtering.

For applications powered from high impedance sources, a tantalum polymer capacitor should be used to buffer the input voltage for the TPS62125. Tantalum polymer capacitors provide a constant capacitance vs. DC bias characteristic compared to ceramic capacitors. In this case, a 10-µF ceramic capacitor should be used in parallel to the tantalum polymer capacitor to provide low ESR.

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 large 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. In case the power is supplied via a connector e.g. from a wall adapter, a hot-plug event can cause voltage overshoots on the VIN pin exceeding the absolute maximum ratings and can damage the device, too. In this case a tantalum polymer capacitor or overvoltage protection circuit reduces the voltage overshoot, see Figure 45.

Table 4 shows a list of input/output capacitors.

Table 4. List of Capacitors

10 0805 GRM21B 25V X5R CIN /COUT Murata
10 0805 GRM21B 16V X5R COUT Murata
22 1206 GRM31CR61 16V X5R COUT Murata
22 B2 (3.5x2.8x1.9) 20TQC22MYFB CIN / input protection Sanyo


Application Curves

TPS62125 effvs_I_1.8V_LPS3314_15uH.gif Figure 12. Efficiency vs. Output Current VOUT = 1.8 V
TPS62125 effvs_I_3.3V_VLF302515_15uH.gif Figure 14. Efficiency vs. Output current, VOUT = 3.3 V
TPS62125 effvsI_5V_LPS3314_10uH.gif Figure 16. Efficiency vs. Output Current, VOUT = 5 V
TPS62125 effvsI_6.8V_LPS3314_10uH.gif Figure 18. Efficiency vs. Output current, VOUT = 6.8 V
TPS62125 effvsI_8V_LPS3314_10uH.gif Figure 20. Efficiency vs. Output Current, VOUT = 8 V
TPS62125 effvsI_10V_LPS3314_10uH.gif Figure 22. Efficiency vs. Output Current, VOUT = 10 V
TPS62125 VO_3.3v_vs_IOUT.gif Figure 24. Output Voltage vs. Output Current, VOUT = 3.3 V
TPS62125 VO_5.0v_vs_IOUT.gif Figure 26. Output Voltage vs. Output current, VOUT = 5 V
TPS62125 VO_6.7v_vs_IOUT.gif Figure 28. Output Voltage vs. Output Current, VOUT = 6.7 V
TPS62125 VO_8.0v_vs_IOUT.gif Figure 30. Output Voltage vs. Output Current, VOUT = 8 V
TPS62125 VO_ripple_ptp_3.3V_25.gif Figure 32. Output Ripple Voltage vs. Output Current,
VOUT = 3.3 V
TPS62125 FSW_VO_5.0V.gif Figure 34. Switch Frequency vs. Output Current, VOUT 5 V
TPS62125 SP_LT_12V_3.3V_1mA.gif Figure 36. Power-Save Mode VOUT= 3.3 V, IOUT = 1 mA
TPS62125 SP_LT_12V_3.3V_5mA_200mA.gif Figure 38. Load Transient 5 mA to 200 mA, VOUT = 3.3 V
TPS62125 SP_LT_12V_5V_1mA_50mA.gif Figure 40. Load Transient 1 mA to 50 mA, VOUT = 5 V
TPS62125 SP_AC_12V_5V_1mA_250mA.gif Figure 42. AC Load Regulation VOUT = 5 V
TPS62125 hp_ovs.gif Figure 44. VIN Hotplug Overshoot
TPS62125 short_circuit_12V_5V_with_IIN.gif Figure 46. Short Circuit and Overcurrent Protection
TPS62125 SP_SU_12V_5.0V_no_EN_comp.gif Figure 48. Operation With EN = VIN, VIN Tracks VOUT
TPS62125 SP_SU_12V_1.8V_10mA.gif Figure 50. Start-Up 1.8 V VOUT
TPS62125 SP_SU_12V_5.0V_10mA.gif Figure 52. Start-Up 5 V VOUT
TPS62125 SP_PG_EN_ON_OFF_12V_3.3V_100R_Load.gif Figure 54. VOUT Ramp Up/Down With EN On/Off
TPS62125 SP_VOUT_ramp_down_PG.gif Figure 56. VOUT Ramp Down With Falling VIN, See Schematic Figure 59
TPS62125 effvs_VIN_1.8V_LPS3314_10uH.gif Figure 13. Efficiency vs. Input Voltage, VOUT = 1.8 V
TPS62125 effvs_VIN_3.3V_VLF302515_15uH.gif Figure 15. Efficiency vs. Input voltage, VOUT = 3.3 V
TPS62125 effvs_VIN_5V_LPS3314_10uH.gif Figure 17. Efficiency vs. Input Voltage, VOUT = 5 V
TPS62125 effvs_VIN_6.8V_LPS3314_10uH.gif Figure 19. Efficiency vs. Input Voltage, VOUT = 6.8 V
TPS62125 effvs_VIN_8V_LPS3314_10uH.gif Figure 21. Efficiency vs. Input Voltage, VOUT = 8 V
TPS62125 effvs_VIN_10V_LPS3314_10uH.gif Figure 23. Efficiency vs. Input Voltage, VOUT = 10 V
TPS62125 VO_3.3V_vs_VIN.gif Figure 25. Output Voltage vs. Input Voltage, VOUT = 3.3 V
TPS62125 VO_5.0V_vs_VIN.gif Figure 27. Output Voltage vs. Input Voltage, VOUT = 5 V
TPS62125 VO_6.7v_vs_VIN.gif Figure 29. Output voltage vs. Input voltage, VOUT = 6.7 V
TPS62125 VO_8.0v_vs_VIN.gif Figure 31. Output Voltage vs. Input Voltage, VOUT = 8 V
TPS62125 FSW_VO_3.3V.gif Figure 33. Switch Frequency vs. Output Current,
VOUT = 3.3 V
TPS62125 FSW_VO_8.0V.gif Figure 35. Switch Frequency vs. Output Current, VOUT = 8 V
TPS62125 SP_LT_12V_3.3V_100mA.gif Figure 37. PWM Mode VOUT= 3.3 V, IOUT = 100 mA
TPS62125 SP_LT_12V_3.3V_ac_5mA_200mA.gif Figure 39. AC Load Regulation, VOUT = 3.3 V
TPS62125 SP_LT_12V_5V_10mA_200mA.gif Figure 41. Load Transient 10 mA to 200 mA, VOUT = 5 V
TPS62125 SP_Line_9V_12V_3.3V_100mA.gif Figure 43. Line Transient Response VIN = 9 V to 12 V
TPS62125 hp_ovs_red.gif Figure 45. VIN Hotplug Overshoot Reduction With Poscap
TPS62125 SP_SU_12V_5.0V_EN_comp.gif Figure 47. Input Supply Voltage Supervisor (SVS),
VOUT = 5 V
TPS62125 SP_SU_0.5mA_source_3.3V.gif Figure 49. 0.5 mA Current Source, 20 mA Pulse Load
TPS62125 SP_SU_12V_3.3V_10mA.gif Figure 51. Start-Up 3.3 V VOUT
TPS62125 SP_SU_12V_8.0V_10mA.gif Figure 53. Start-Up 8 V VOUT
TPS62125 SP_VOUT_discharge_VO_3.3V.gif Figure 55. Output Discharge Using PG Pin, Triggered by EN Comparator

System Examples

TPS62125 5-V Output Voltage Configuration

TPS62125 TPS62125_app_5V.gif Figure 57. TPS62125 5-V Output Voltage Configuration

TPS62125 5-V VOUT

TPS62125 TPS62125_app_5V_enhys_VIN_ramp.gif Figure 58. TPS62125 5-V VOUT, Start-up Voltage VIN_Start = 10 V, Stop Voltage VIN_Stop = 6 V, See Figure 47

TPS62125 Operation From a Storage Capacitor Charged From a 0.5 mA Current Source

TPS62125 TPS62125_app_3.3V_SUP_buffercap.gif Figure 59. TPS62125 Operation From a Storage Capacitor Charged From a 0.5 mA Current Source,
VOUT = 3.3 V, See Figure 49

5 V to –5 V Inverter Configuration

TPS62125 TPS62125_app_inverter_-5V.gif Figure 60. 5 V to –5 V Inverter Configuration, See SLVA514