SNVS178H January   2002  – December 2015 LM3485

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 Hysteretic Control Circuit
      2. 7.3.2 Current Limit Operation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Start Up
      2. 7.4.2 External Sense Resistor
      3. 7.4.3 PGATE
  8. 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 Step by Step Design Procedure
        2. 8.2.2.2 Inductor Selection (L1)
        3. 8.2.2.3 Output Voltage Set Point
        4. 8.2.2.4 Output Capacitor Selection (COUT)
        5. 8.2.2.5 Input Capacitor Selection (CIN)
        6. 8.2.2.6 Programming the Current Limit (RADJ)
        7. 8.2.2.7 Catch Diode Selection (D1)
        8. 8.2.2.8 P-Channel MOSFET Selection (Q1)
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
  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

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6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)
MIN TYP MAX UNIT
PGATE voltage −0.3 36 V
FB voltage −0.3 5 V
ISENSE voltage −1.0 36 V
ADJ voltage −0.3 36 V
Maximum junction temperature 150 °C
Power dissipation (at TA = 25°C) 417 mW
Lead temperature Vapor phase (60 sec.) 215 °C
Infrared (15 sec.) 220 °C
Storage temperature, Tstg −65 160 °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.

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

MIN NOM MAX UNIT
Supply voltage 4.5 35 V
TJ Operating junction temperature −40 125 °C

6.4 Thermal Information

THERMAL METRIC(1) LM3485 UNIT
DGK (VSSOP)
8 PINS
RθJA Junction-to-ambient thermal resistance 163.3 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 56.7 °C/W
RθJB Junction-to-board thermal resistance 83.2 °C/W
ψJT Junction-to-top characterization parameter 5.9 °C/W
ψJB Junction-to-board characterization parameter 81.9 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance N/A °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

Specifications are for TJ = 25°C. Unless otherwise specified, VIN = 12 V, VISNS = VIN − 1 V, and VADJ = VIN − 1.1 V. Data sheet minimum and maximum specification limits are specified by design, test, or statistical analysis.
PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT
IQ Quiescent current at ground pin FB = 1.5 V (Not Switching) 250 µA
(TJ = −40°C to 125°C) 400
VFB Feedback voltage(3) 1.226 1.242 1.258 V
(TJ = −40°C to 125°C) 1.217 1.267
VHYST Comparator hysteresis 10 15 mV
(TJ = −40°C to 125°C) 14 20
VCL(4) Current limit comparator trip voltage RADJ = 20 kΩ 110 mV
RADJ = 160 kΩ 880
VCL_OFFSET Current limit comparator offset VFB = 1.5 V 0 mV
(TJ = −40°C to 125°C) −20 20
ICL_ADJ Current limit ADJ current source VFB = 1.5 V 5.5 µA
(TJ = −40°C to 125°C) 3.0 7.0
TONMIN_CLCL Current limit one shot off time VADJ = 11.5 V
VISNS = 11.0 V
VFB = 1.0 V		 9 µs
(TJ = −40°C to 125°C) 6 14
RPGATE Driver resistance Source
ISOURCE = 100 mA		 5.5 Ω
Sink
ISink = 100 mA		 8.5
IPGATE Driver output current Source
VIN = 7 V,
PGATE = 3.5 V		 0.44 A
Sink
VIN = 7 V,
PGATE = 3.5 V		 0.32
IFB FB pin bias current(5) VFB = 1.0 V 300 nA
(TJ = −40°C to 125°C) 750
TONMIN_NOR Minimum on time in normal operation VISNS = VADJ + 0.1 V
Cload on OUT = 1000 pF(6)		 100 ns
T Minimum on time in current limit VISNS = VADJ + 0.1 V
VFB = 1.0 V
Cload on OUT = 1000 pF(6)		 175 ns
%VFB/ΔVIN Feedback voltage line regulation 4.5 ≤ VIN ≤ 35 V 0.010%
(1) All limits are at room temperature unless otherwise specified. All room temperature limits are 100% tested. All limits at temperature extremes are specified via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
(2) Typical numbers are at 25°C and represent the most likely norm.
(3) The VFB is the trip voltage at the FB pin when PGATE switches from high to low.
(4) VCL = ICL_ADJ × RADJ
(5) Bias current flows out from the FB pin.
(6) A 1000-pF capacitor is connected between VIN and PGATE.

6.6 Typical Characteristics

Unless otherwise specified, TJ = 25°C
LM3485 20034601.gif
FB = 1.5 V
Figure 1. Quiescent Current vs Input Voltage
LM3485 20034605.gif
Figure 3. Hysteresis Voltage vs Input Voltage
LM3485 20034602.gif
Figure 5. Current Limit ADJ Current vs Temperature
LM3485 20034603.gif
Figure 7. PGATE Voltage vs Input Voltage
LM3485 20034612.gif
Figure 9. Minimum ON-Time vs Temperature
LM3485 20034640.gif
VIN = 12 V
Figure 11. Operating ON-Time vs Output Load Current
LM3485 20034618.gif
VOUT = 3.3 V L = 22 µH
Figure 13. Efficiency vs Load Current
LM3485 20034620.gif
Figure 15. Start Up
LM3485 20034616.gif
VIN = 12 V VOUT = 3.3 V IOUT = 50 mA
L = 22 µH
Figure 17. Discontinuous Mode Operation
LM3485 20034643.gif
VOUT = 3.3 V IOUT = 1 A COUT(ESR) = 80 mΩ
Cff = 100 pF
Figure 19. Output Ripple Voltage vs Input Voltage
LM3485 20034630.gif
VOUT = 3.3 V
L = 22 µH
IOUT = 500 mA
Figure 21. Feed-Forward Capacitor (Cff) Effect
LM3485 20034607.gif
Figure 2. Feedback Voltage vs Temperature
LM3485 20034606.gif
Figure 4. Hysteresis Voltage vs Temperature
LM3485 20034604.gif
Figure 6. Current Limit One-Shot OFF-Time vs Temperature
LM3485 20034645.gif
VIN = 9 V
Figure 8. Typical VPGATE vs Time
LM3485 20034622.gif
VIN = 4.5 V
Figure 10. Operating ON-Time vs Output Load Current
LM3485 20034617.gif
VOUT = 3.3 V L = 6.8 µH
Figure 12. Efficiency vs Load Current
LM3485 20034631.gif
VOUT = 5.0 V L = 22 µH
Figure 14. Efficiency vs Load Current
LM3485 20034615.gif
VIN = 12 V VOUT = 3.3 V IOUT = 500 mA
L = 22 µH
Figure 16. Continuous Mode Operation
LM3485 20034613.gif
VOUT = 3.3 V IOUT = 1 A COUT(ESR) = 80 mΩ
Cff = 100 pF
Figure 18. Operating Frequency vs Input Voltage
LM3485 20034621.gif
L = 22 µH COUT(ESR) = 45 mΩ Cff = 100 pF
Figure 20. Operating Frequency vs Output Load Current