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Numéro de sérieLM3421
CategoriePower Management => Lighting Controllers
DescriptionN-Channel Controllers For Constant Current LED Drivers From The PowerWise® Family
The LM3421/LM3423 devices are versatile high voltage LED driver controllers. With the capability to be configured in a Buck, Boost, Buck-Boost (Flyback), or SEPIC topology, and an input operating voltage rating of 75V, these controllers are ideal for illuminating LEDs in a very diverse, large family of applications.
SociétéNational Semiconductor Corporation
DatasheetTélécharger LM3421 datasheet
 
 
  • Description courte

  • The LM3421/LM3423 devices are versatile high voltage LED driver controllers. With the capability to be configured in a Buck, Boost, Buck-Boost (Flyback), or SEPIC topology, and an input operating voltage rating of 75V, these controllers are ideal for illuminating LEDs in a very diverse, large family of applications. Adjustable high-side current sense with a typical sense voltage of 100mV allows for tight regulation of the LED current with the highest efficiency possible. Output LED current regulation is based on peak current-mode control with predictive Off-Time Control. This method of control eases the design of loop compensation while providing inherent input voltage feed-forward compensation. The LM3421/LM3423 include a high-voltage startup regulator that operates over a wide input range to 75V. The internal PWM controller is designed for adjustable switching frequencies to 2.0MHz, thus enabling compact solutions. Additional features include: "zero" current shutdown, precision reference, logic compatible DIM input suitable for fast PWM dimming, cycle-by-cycle current limit, and thermal shutdown. The LM3423 also includes an LED output status flag, a fault flag, a programmable fault timer, and a logic input to select the polarity of the dimming output driver.

    Features

    VIN range from 75V 2% Internal reference voltage (1.235V) Current sense voltage adjustable from 20mV High-side current sensing 2 MOSFET gate driver Dimming MOSFET gate driver Input under-voltage protection Over-voltage protection Low shutdown current, < 1µA Fast (50kHz) PWM dimming Cycle-by-cycle current limit Programmable switching frequency LED output status flag (LM3423 only) Fault timer pin (LM3423 only) TSSOP EP 16-lead package (LM3421) TSSOP EP 20-lead package (LM3423)

    Applications

    LED Drivers Constant-Current Buck-Boost Regulator Constant-Current Boost Regulator Constant-Current Flyback Regulator Constant-Current SEPIC Regulator Thermo-Electric Cooler (Peltier) Driver

    Order Number LM3423MH LM3423MHX Spec. NOPB Package Type TSSOP-20 EP NSC Package Drawing MXA20A 92 Units, Rail 2500 Units, Tape and Reel 73 Units, Rail 2500 Units, Tape and Reel Supplied As

    LM3423 LM3421 Name VIN EN COMP CSH Function Power supply input (4.5V-75V). Bypass with 100nF capacitor to AGND as close to the device as possible in the circuit board layout. Enable: Pull to ground for zero current shutdown. Tie directly to VIN for automatic startup at 4.1V. Compensation: PWM controller error amplifier compensation pin. This pin connects through a series resistor-capacitor network to AGND. Current Sense High: Output of the high side sense amplifier and input to the main regulation loop error amplifier. Resistor Capacitor Timing: External RC network sets the predictive "off-time" and thus the switching frequency. The RC network should be placed as close to the device as possible in the circuit board layout. Analog Ground: The proper place to connect the compensation and timing capacitor returns. This pin should be connected via the circuit board to the PGND pin through the EP copper circuit board pad. Over-Voltage Protection sense input: 1.24V threshold with hysteresis that is user programmable by the selection of the OVP Over-Voltage Lock-Out (OVLO) resistor divider network. Not DIM input: Dual function pin. Primarily used as the Pulse Width Modulation (PWM) input. When driven with a resistor divider from VIN, this pin also functions as a user programmable VIN Under-Voltage Lock-Out (UVLO) with 1.24V threshold and programmable hysteresis by the UVLO resistor divider network. The PWM and UVLO functions can be performed simultaneously. Fault flag: This is an N-channel MOSFET open drain output. The FLT pin transitions to the high (open) state once the Fault Timer has timed out and latched the controller off.

    Function Fault Timer: The fault timer is comprised of an external capacitor, an internal charging current source, an internal discharge N-channel MOSFET, and a comparator that latches the fault condition when the threshold voltage (1.24V) is exceeded. LED Ready status flag: This is an N-channel MOSFET open drain output which pulls down whenever the LED current is not in regulation. Dim Polarity: Selects the polarity of the DIM driver output. Tie to VCC or leave open for low side dimming, tie to ground for high side dimming. External Dimming MOSFET Gate Drive: Gate driver output responding to nDIM input. Power Ground: GATE and DDRV gate drive ground current return pin. This pin should be connected via the circuit board to the AGND pin through the EP copper circuit board pad. Main switching MOSFET gate drive output. Internal Regulator Bypass: 6.9V low dropout linear regulator output. Bypass with 2.2µF­ 3.3µF, ceramic type capacitor to PGND. Main Switch Current Sense input: This pin is used for current mode control and cycle-by-cycle current limit. This pin can be tied to the drain of the main N-channel MOSFET switch for RDS(ON) sensing or tied to a sense resistor installed in the source of the same device. Resistor Pull-Down: This is an open drain N-channel MOSFET which is used to pull-down the low side of all external resistor dividers (VIN UVLO, OVP). This pin allows for system "zerocurrent" shutdown. High Side Sense Positive: LED current sense positive input. An external resistor sets a reference current flowing into this pin from the programmed high-side sense voltage. Although the current into this pin can be set to values ranging from 10µA through 1mA, a value 100µA is recommended. This pin is a virtual ground whose potential is set by the voltage on the HSN pin. High Side Sense Negative: This pin sets the reference voltage for the HSP input. An external resistor of the same value as that used on the HSP pin should be connected from this pin to the negative side of the current sense resistor. EP: Star ground, connecting AGND and PGND. For thermal considerations please refer to (Note 4) of the Electrical Characteristics table.