SNVS322M December   2004  – December 2015 LP38690 , LP38692


  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 Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Enable (EN)
      2. 7.3.2 Thermal Shutdown Protection (TSD)
      3. 7.3.3 Foldback Current Limiting
    4. 7.4 Device Functional Modes
      1. 7.4.1 Enable (EN)
      2. 7.4.2 Minimum Operating Input Voltage (VIN)
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Reverse Voltage
    2. 8.2 Typical Applications
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. Power Dissipation and Device Operation
        2. External Capacitors
          1. Input Capacitor
          2. Output Capacitor
          3. No Load Stability
          4. Capacitor Characteristics
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 PCB Layout
    2. 10.2 Layout Examples
    3. 10.3 WSON Mounting
    4. 10.4 RFI/EMI Susceptibility
    5. 10.5 Output Noise
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Related Links
    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

8 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.

8.1 Application Information

8.1.1 Reverse Voltage

A reverse voltage condition exists when the voltage at the output pin is higher than the voltage at the input pin. Typically this happens when VIN is abruptly taken low and COUT continues to hold a sufficient charge such that the input to output voltage becomes reversed. A less common condition is when an alternate voltage source is connected to the output.

There are two possible paths for current to flow from the output pin back to the input during a reverse voltage condition.

  1. While VIN is high enough to keep the control circuitry alive, and the EN pin (LP38692 only) is above the VEN(ON) threshold, the control circuitry attempts to regulate the output voltage. If the input voltage is less than the programmed output voltage, the control circuit drives the gate of the pass element to the full ON condition. In this condition, reverse current flows from the output pin to the input pin, limited only by the RDS(ON) of the pass element and the output to input voltage differential. Discharging an output capacitor up to 1000 μF in this manner does not damage the device as the current will rapidly decay. However, continuous reverse current should be avoided. When the EN pin is low this condition is prevented.
  2. The internal PFET pass element has an inherent parasitic diode. During normal operation, the input voltage is higher than the output voltage and the parasitic diode is reverse biased. However, when VIN is below the value where the control circuitry is alive, or the EN pin is low (LP38692 only), and the output voltage is more than 500 mV (typical) above the input voltage the parasitic diode becomes forward biased and current flows from the output pin to the input pin through the diode. The current in the parasitic diode should be limited to less than 1 A continuous and 5 A peak.
  3. If used in a dual-supply system where the regulator output load is returned to a negative supply, the output pin must be diode clamped to ground to limit the negative voltage transition. A Schottky diode is recommended for this protective clamp.

8.2 Typical Applications

LP38690 LP38692 20126601.gif
* Minimum value required for stability.
**WSON package devices only.
Figure 30. LP38690 Typical Application
LP38690 LP38692 20126602.gif
* Minimum value required for stability.
**WSON package devices only.
Figure 31. LP38692 Typical Application

8.2.1 Design Requirements

For typical CMOS voltage regulator applications, use the parameters listed in Table 1.

Table 1. Design Parameters

Input voltage range 2.7 to 10 V
Output voltage 1.8 V
Output current 1 A
Output capacitor range 1 µF
Input/output capacitor ESR range 5 mΩ to 500 mΩ

8.2.2 Detailed Design Procedure Power Dissipation and Device Operation

The permissible power dissipation for any package is a measure of the capability of the device to pass heat from the power source, the junctions of the device, to the ultimate heat sink, the ambient environment. Thus, the power dissipation is dependent on the ambient temperature and the thermal resistance across the various interfaces between the die junction and ambient air.

The permissible power dissipation for any package is a measure of the capability of the device to pass heat from the power source, the junctions of the device, to the ultimate heat sink, the ambient environment. Thus, the power dissipation is dependent on the ambient temperature and the thermal resistance across the various interfaces between the die junction and ambient air.

The maximum allowable power dissipation for the device in a given package can be calculated using Equation 1:

Equation 1. PD-MAX = ((TJ-MAX – TA) / RθJA)

The actual power being dissipated in the device can be represented by Equation 2:

Equation 2. PD = (VIN – VOUT) × IOUT

These two equations establish the relationship between the maximum power dissipation allowed due to thermal consideration, the voltage drop across the device, and the continuous current capability of the device. These two equations should be used to determine the optimum operating conditions for the device in the application.

In applications where lower power dissipation (PD) and/or excellent package thermal resistance (RθJA) is present, the maximum ambient temperature (TA-MAX) may be increased.

In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature (TA-MAX) may have to be derated. TA-MAX is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125°C), the maximum allowable power dissipation in the device package in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (RθJA), as given by Equation 3:

Equation 3. TA-MAX = (TJ-MAX-OP – (RθJA × PD-MAX))

Alternately, if TA-MAX can not be derated, the PD value must be reduced. This can be accomplished by reducing VIN in the VIN – VOUT term as long as the minimum VIN is met, or by reducing the IOUT term, or by some combination of the two. External Capacitors

In common with most regulators, the LP38690 and LP38692 require external capacitors for regulator stability. The LP38690 and LP38692 are specifically designed for portable applications requiring minimum board space and smallest components. These capacitors must be correctly selected for good performance. Input Capacitor

An input capacitor is required for stability. It is recommended that a 1-μF capacitor be connected between the LP38690 or LP38692 IN pin and GND pin (this capacitance value may be increased without limit). This capacitor must be located a distance of not more than 1 cm from the IN pin and returned to a clean analogue ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.

Important: To ensure stable operation it is essential that good PCB design practices are employed to minimize ground impedance and keep input inductance low. If these conditions cannot be met, or if long leads are used to connect the battery or other power source to the LP38690 or LP38692, then it is recommended that the input capacitor is increased. Also, tantalum capacitors can suffer catastrophic failures due to surge current when connected to a low-impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input, it must be ensured by the manufacturer to have a surge current rating sufficient for the application.

There are no requirements for the equivalent series resistance (ESR) on the input capacitor, but tolerance and temperature coefficient must be considered when selecting the capacitor to ensure the capacitance remains approximately 1 μF over the entire operating temperature range. Output Capacitor

The LP38690 and LP38692 are designed specifically to work with very small ceramic output capacitors. A 1-μF ceramic capacitor (temperature types Z5U, Y5V or X7R/X5R) with ESR between 5 mΩ to 500 mΩ, is suitable in the LP38690 or LP38692 application circuit.

For this device the output capacitor should be connected between the OUT pin and GND pin. It is also possible to use tantalum or film capacitors at the device output, but these are not as attractive for reasons of size and cost (see Capacitor Characteristics). The output capacitor must meet the requirement for the minimum value of capacitance and also have an ESR value that is within the range 5 mΩ to 500 mΩ for stability. No Load Stability

The LP38690 and LP38692 remain stable and in regulation with no external load. This is an important consideration in some circuits, for example CMOS RAM keep-alive applications. Capacitor Characteristics

The LP38690 and LP38692 are designed to work with ceramic capacitors on the output to take advantage of the benefits they offer. For capacitance values in the range of 0.47 μF to 4.7 μF, ceramic capacitors are the smallest, least expensive and have the lowest ESR values, thus making them best for eliminating high frequency noise. The ESR of a typical 1-μF ceramic capacitor is in the range of 20 mΩ to 40 mΩ, which easily meets the ESR requirement for stability for the LP38690 or LP38692.

For both input and output capacitors, careful interpretation of the capacitor specification is required to ensure correct device operation. The capacitor value can change greatly, depending on the operating conditions and capacitor type.

In particular, the output capacitor selection should take account of all the capacitor parameters, to ensure that the specification is met within the application. The capacitance can vary with DC bias conditions as well as temperature and frequency of operation. Capacitor values also shows some decrease over time due to aging. The capacitor parameters are also dependent on the particular case size, with smaller sizes giving poorer performance figures in general. As an example, Figure 32 shows a typical graph comparing different capacitor case sizes in a capacitance vs DC bias plot. As shown in Figure 32, increasing the DC Bias condition can result in the capacitance value falling below the minimum value given in the recommended capacitor specifications table (0.7 μF in this case). Note that the graph shows the capacitance out of spec for the 0402 case size capacitor at higher bias voltages. It is therefore recommended that the capacitor manufacturers’ specifications for the nominal value capacitor are consulted for all conditions, as some capacitor sizes (for example, 0402) may not be suitable in the actual application.

LP38690 LP38692 30017828.gif Figure 32. Typical Variation In Capacitance vs DC Bias

The ceramic capacitor’s value varies with temperature. The capacitor type X7R, which operates over a temperature range of –55°C to 125°C, only varies the capacitance to within ±15%. The capacitor type X5R has a similar tolerance over a reduced temperature range of –55°C to 85°C. Many large value ceramic capacitors, larger than 1 μF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by more than 50% as the temperature varies from 25°C to 85°C. Therefore, X7R and X5R types are recommended over Z5U and Y5V in applications where the ambient temperature changes significantly above or below 25°C.

Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more costly when comparing equivalent capacitance and voltage ratings in the 0.47-μF to 4.7-μF range. Another important consideration is that tantalum capacitors have higher ESR values than equivalent size ceramic capacitors. This means that while it may be possible to find a tantalum capacitor with an ESR value within the stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the same ESR value. It should also be noted that the ESR of a typical tantalum increases about 2:1 as the temperature goes from 25°C down to -40°C, so some guard band must be allowed.

8.2.3 Application Curves

LP38690 LP38692 20126661.png
Figure 33. VOUT vs VEN, On (LP38692 Only)
LP38690 LP38692 20126662.png
Figure 34. VOUT vs VEN, Off (LP38692 Only)