SNVS416C November   2005  – February 2016 LM27951

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Charge Pump
      2. 7.3.2 Soft Start
      3. 7.3.3 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Enable and PWM Pins
      2. 7.4.2 Adjusting LED Brightness (PWM Control)
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Maximum Output Current, Maximum LED Voltage, Minimum Input Voltage
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Setting LED Currents
        2. 8.2.2.2 Capacitor Selection
        3. 8.2.2.3 Parallel Dx Outputs for Increased Current Drive
        4. 8.2.2.4 Power Efficiency
        5. 8.2.2.5 Power Dissipation
      3. 8.2.3 Application Curves
  9. 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 Documentation Support
      1. 11.2.1 Related Documentation
    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

6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN MAX UNIT
VIN –0.3 6 V
EN, PWM –0.3 VIN + 0.3(3) V
Continuous power dissipation Internally limited
Junction temperature, TJ-MAX-ABS 150 °C
Lead temperature (Soldering, 5 sec.) 260 °C
Storage temperature, Tstg –65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office / Distributors for availability and specifications.
(3) Maximum value is 6 V.
(4) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at(4) TJ =150°C (typical) and disengages at TJ = 140°C (typical).

6.2 ESD Ratings

VALUE UNIT
V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 V
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)(1)(2)(3)
MIN NOM MAX UNIT
Inpu voltage, VIN 2.8 5.5 V
LED voltage 2.5 3.9 V
Junction temperature, TJ –40 115 °C
Ambient temperature, TA –40 85 °C
(1) All voltages are with respect to the potential at the GND pin.
(2) Minimum and maximum limits are ensured by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most likely norm.
(3) In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operation junction temperature (TJ-MAX-OP = 115°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (RθJA), as given by the equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).

6.4 Thermal Information

THERMAL METRIC(1) LM27951 UNIT
NHK (WSON)
14 PINS
RθJA Junction-to-ambient thermal resistance 42.5 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 33.3 °C/W
RθJB Junction-to-board thermal resistance 14.1 °C/W
ψJT Junction-to-top characterization parameter 0.5 °C/W
ψJB Junction-to-board characterization parameter 14.1 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance 6.1 °C/W
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report, SPRA953.

6.5 Electrical Characteristics

Unless otherwise noted, typical limits are for TA = 25°C, and minimum and maximum limits apply over the full operating temperature (–40°C to +85°C); specifications apply to the Simplified Schematic with VIN = 3.6 V, V(EN) = 1.8 V, V(PWM) = 1.8 V, 4 LEDs, VDX = 3.6 V, CIN = COUT = 3.3 µF, C1 = C2 = 1 µF, RSET = 12.5 kΩ(1) (2).
PARAMETER TEST CONDITIONS MIN
 TYP MAX
 UNIT
IDX LED current regulation 3 V ≤ VIN ≤ 5.5 V
RSET = 12.5 kΩ
IVOUT = 0 mA		 18.4
(−8%)		 20 21.6
(8%)		 mA
3 V ≤ VIN ≤ 5.5 V
RSET = 8.32 kΩ
IVOUT = 0 mA		 30
3 V ≤ VIN ≤ 5.5 V
RSET = 24.9 kΩ
IVOUT = 0 mA		 10
ID-MATCH LED current matching(3) RSET = 8.32 kΩ 0.2 1.5%
IQ Quiescent supply current D(1-4) = OPEN
RSET = OPEN		 1.5 1.9 mA
ISD Shutdown supply current 3 V ≤ VIN ≤ 5.5 V
V(EN) = 0 V		 0.1 1 µA
VSET ISET pin voltage 3 V ≤ VIN ≤ 5.5 V 1.25 V
IDX / ISET Output current to current set ratio 200
VHR Current source voltage headroom requirement(4) IDX = 95% IDX (nominal)
RSET = 8.32 kΩ
(IDX nominal = 30 mA)		 360 mV
IDX = 95% IDX (nom.)
RSET = 12.5 kΩ
(IDX nom. = 20 mA)		 240
fSW Switching frequency 525
(–30%) 		750 975
(30%) 		kHz
VIH Logic input high Input pins: EN, PWM
3 V ≤ VIN ≤ 5.5 V		 1 VIN V
VIL Logic input low Input pins: EN, PWM
3 V ≤ VIN ≤ 5.5 V		 0 0.4
IIH Logic input high current Input pin: PWM
V(PWM) = 1.8 V		 10 nA
Input pin: EN
V(EN) = 1.8 V(5)		 12 µA
IIL Logic input low current Input pins: EN, PWM
V(EN, PWM) = 0 V		 10 nA
ROUT Charge pump output resistance (6) 3.3 Ω
VGDX 1× to 3/2× gain transition voltage threshold on VDX (VOUT − VDX) Falling 500 mV
tON Start-up time IDX = 90% steady state 330 µs
(1) All voltages are with respect to the potential at the GND pin.
(2) CIN, COUT, C1, C2: Low-ESR surface-mount ceramic capacitors (MLCCs) used in setting electrical characteristics.
(3) LED current matching is based on two calculations: [(IMAX – IAVG) / IAVG] and [(IAVG – IMIN) / IAVG]. IMAX and IMIN are the highest and lowest respective Dx currents, and IAVG is the average Dx current of all four current sources. The largest number of the two calculations (worst case) is considered the matching figure for the part. The typical specification provided is the most likely norm of the matching figure for all parts.
(4) Headroom voltage (VHR) = VOUT − VDX. If headroom voltage requirement is not met, LED current regulation may be compromised.
(5) EN logic input high current (IIH) is due to a 150-kΩ (typical) pulldown resistor connected internally between the EN and GND pins.
(6) The open-loop output resistance (ROUT) models all voltage losses in the charge pump. ROUT can be used to estimate the voltage at the charge pump output VOUT and the maximum current capability of the device under low VIN and high IOUT conditions, beyond what is specified in the electrical specifications table: VOUT = (G × VIN) – (ROUT × IOUT). In the equation, G is the charge-pump-gain mode, and IOUT is the total output current (sum of all active Dx current sources and all current drawn from VOUT).

6.6 Typical Characteristics

Unless otherwise specified: TA = 25°C, 4 LEDs, VDX = 3.6 V, VIN = 3.6 V, VEN = VIN, VPWM = VIN, C1 = C2 = 1µF, CIN = COUT = 3.3 µF. Capacitors are low-ESR multi-layer ceramic capacitors (MLCCs).
LM27951 20171704.png
Figure 1. LED Current Regulation vs Input Voltage
LM27951 20171712.png
  
VIN = 3.6V Time scale: 400 ns/Div Load = 15 mA/LED, 4 LEDs
CH1 (TOP): VIN; Scale: 20mV/Div, AC Coupled
CH2 (BOTTOM): VOUT; Scale: 20mV/Div, AC Coupled
Figure 3. Input and Output Voltage Ripple
LM27951 20171706.png
Figure 2. Average LED Current Regulation vs Input Voltage
LM27951 20171713.png
     
VIN = 3.6 V Time scale: 100 µs/Div Load = 20mA/LED, 4 LEDs
CH1 (TOP): VEN; Scale: 1 V/Div
CH2 (BOTTOM): VOUT; Scale: 1 V/Div
Figure 4. Start-Up Response