SM72485/NOPB

Manufacturer Part NumberSM72485/NOPB
DescriptionIC BUCK SWITCH 100V REG 8-LLP
ManufacturerNational Semiconductor
SeriesSolarMagic™
TypeStep-Down (Buck)
SM72485/NOPB datasheet
 

Specifications of SM72485/NOPB

Internal Switch(s)YesSynchronous RectifierNo
Number Of Outputs1Voltage - OutputAdj to 2.5V
Current - Output150mAFrequency - Switching50kHz ~ 1.1MHz
Voltage - Input6 V ~ 95 VOperating Temperature-40°C ~ 125°C
Mounting Type*Package / Case*
Lead Free Status / RoHS StatusLead free / RoHS Compliant  
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SolarMagic 100V, 150 mA Constant On-Time Buck
Switching Regulator
General Description
The SM72485 Step Down Switching Regulator features all of
the functions needed to implement a low cost, efficient, Buck
bias regulator. This high voltage regulator contains an 100 V
N-Channel Buck Switch. The device is easy to implement and
is provided in the thermally enhanced LLP-8 package. The
regulator is based on a control scheme using an ON time in-
versely proportional to V
. This feature allows the operating
IN
frequency to remain relatively constant. The control scheme
requires no loop compensation. An intelligent current limit is
implemented with forced OFF time, which is inversely pro-
portional to Vout. This scheme ensures short circuit control
while providing minimum foldback. Other features include:
Thermal Shutdown, V
under-voltage lockout, Gate drive
CC
under-voltage lockout, Max Duty Cycle limiter, and a pre-
charge switch.
Features
Renewable Energy Grade
Operating input voltage range: 6V to 95V
Integrated 100V, N-Channel buck switch
Internal start-up regulator
No loop compensation required
Ultra-Fast transient response
Typical Application, Basic Step-Down Regulator
© 2011 National Semiconductor Corporation
SM72485
On time varies inversely with input voltage
Operating frequency remains constant with varying line
voltage and load current
Adjustable output voltage from 2.5V
Highly efficient operation
Precision internal reference
Low bias current
Intelligent current limit
Thermal shutdown
Typical Applications
Non-Isolated Telecommunication Buck Regulator
Secondary High Voltage Post Regulator
+42V Automotive Systems
Package
LLP - 8 (4mm x 4mm)
301423
February 25, 2011
30142301
www.national.com

SM72485/NOPB Summary of contents

  • Page 1

    ... Internal start-up regulator ■ No loop compensation required ■ Ultra-Fast transient response Typical Application, Basic Step-Down Regulator © 2011 National Semiconductor Corporation SM72485 ■ On time varies inversely with input voltage ■ Operating frequency remains constant with varying line voltage and load current ■ ...

  • Page 2

    Connection Diagram Ordering Information Order Number Package Type SM72485E SM72485 SM72485X Pin Descriptions Pin Name Description 1 SW Switching Node 2 BST Boost Pin (Boot–strap capacitor input) 3 RCL Current Limit OFF time set pin 4 RTN Ground pin 5 ...

  • Page 3

    ... Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications GND IN BST to GND SW to GND (Steady State) ESD Rating (Note 5) Human Body Model BST Electrical Characteristics apply over full Operating Junction Temperature range. V ...

  • Page 4

    ... For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: For detailed information on soldering plastic LLP packages, refer to the Packaging Data Book available from National Semiconductor Corporation. Note 3: All limits are guaranteed. All electrical characteristics having room temperature limits are tested during production with T limits are guaranteed by correlating the electrical characteristics to process and temperature variations and applying statistical process control ...

  • Page 5

    Typical Performance Characteristics Efficiency vs. Load Current and V (Circuit of Figure ON-Time vs Input Voltage and R Maximum Frequency vs 30142324 Current Limit Off-Time vs 30142325 and V I OUT IN CC 30142326 5 ...

  • Page 6

    Block Diagram Functional Description The SM72485 Step Down Switching Regulator features all the functions needed to implement a low cost, efficient, Buck bias power converter. This high voltage regulator contains a 100 V N-Channel Buck Switch, is easy to implement ...

  • Page 7

    The SM72485 regulates the output voltage based on ripple voltage at the feedback input, requiring a minimum amount of ESR for the output capacitor C2. A minimum of 25mV to 50mV of ripple voltage at the feedback pin (FB) is ...

  • Page 8

    Regulation Comparator The feedback voltage compared to an internal 2.5V reference. In normal operation (the output voltage is regulat- ed), an on-time period is initiated when the voltage at FB falls below 2.5V. The buck switch will ...

  • Page 9

    FIGURE 3. Shutdown Implementation Current Limit The SM72485 contains an intelligent current limit OFF timer. If the current in the Buck switch exceeds 0.3A the present cycle is immediately terminated, and a non-resetable OFF timer is initiated. The length of ...

  • Page 10

    SM72485’s current limit threshold (360 mA) with- out saturating, since the current limit is reached during start- up. The ...

  • Page 11

    ... Kemet C1206C103K5RAC TDK C3216X7R2A104M Diodes Inc. DFLS1100 COILTRONICS DR125-221-R, or TDK SLF10145T-221MR65 Vishay CRCW12063011F Vishay CRCW12061001F Vishay CRCW12063R30F Vishay CRCW12063093F Vishay CRCW12063163F National Semiconductor SM72485 11 30142318 Value 1 µF, 100V 22 µF, 25V 0.47 µF, 50V 0.01 µF, 50V 0.1 µF, 100V 100V, 1A 220 µH 3.01 kΩ ...

  • Page 12

    LOW OUTPUT RIPPLE CONFIGURATIONS For applications where low output ripple is required, the fol- lowing options can be used to reduce or nearly eliminate the ripple. a) Reduced ripple configuration: In across R to AC-couple the ripple at V FB2 ...

  • Page 13

    Minimum ripple configuration: If the application requires a lower value of ripple (<10 mVp-p), the circuit of be used removed, and the resulting output ripple volt- age is determined by the inductor’s ripple current and C2’s characteristics. ...

  • Page 14

    FIGURE 9. Alternate Minimum Output Ripple 14 30142323 ...

  • Page 15

    Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead LLP Package NS Package Number SDC08B 15 www.national.com ...

  • Page 16

    ... For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Amplifiers www.national.com/amplifiers Audio www.national.com/audio Clock and Timing www.national.com/timing Data Converters www.national.com/adc Interface www.national.com/interface LVDS www.national.com/lvds Power Management www.national.com/power Switching Regulators www.national.com/switchers LDOs www.national.com/ldo LED Lighting www ...