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MIC3230 Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC3230 Datasheet(HTML) 9 Page - Micrel Semiconductor |
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9 / 20 page  Micrel, Inc. MIC3230/1/2 January 2009 9 M9999-011409-A Power Topology Constant Output Current Controller The MIC323x family are peak current mode boost controllers designed to drive high power LEDs. Unlike a standard constant output voltage controller, the MIC323x family has been designed to provide a constant output current. The MIC323x family is designed for a wide input voltage range, from 6V to 45V. In the boost configuration, the output can be set from VIN up to 100V. As a peak current mode controller, the MIC323x family provides the benefits of superior line transient response as well as an easier to design compensation. This family of LED drivers features a built-in soft-start circuitry in order to prevent start-up surges. Other protection features include: • Current Limit (ILIMIT) - Current sensing for over current and overload protection • Over Voltage Protection (OVP) - Output over voltage protection to prevent operation above a safe upper limit • Under Voltage Lockout (UVLO) – UVLO designed to prevent operation at very low input voltages Setting the LED Current The current through the LED string is set via the value chosen for the current sense resistor, RADJ. This value can be calculated using Equation 1: Eq. (1) ADJ LED R V I 25 . 0 = Another important parameter to be aware of in the boost controller design, is the ripple current. The amount of ripple current through the LED string is equal to the output ripple voltage divided by the LED AC resistance (RLED – provided by the LED manufacturer) plus the current sense resistor (RADJ). The amount of allowable ripple through the LED string is dependent upon the application and is left to the designer’s discretion. This equation is shown in Equation 2: Eq. (2) ) ( ADJ LED OUT LED R R V I RIPPLE + ≈ Δ Where OUT LED OUT C T D I V RIPPLE × × = Reference Voltage The voltage feedback loop of the MIC323x uses an internal reference voltage of 0.25V with an accuracy of ±3%. The feedback voltage is the voltage drop across the current setting resistor (RADJ) as shown in Figure 1. When in regulation the voltage at IADJ will equal 0.25V. Output Over Voltage Protection (OVP) The MIC323x provides an OVP circuitry in order to help protect the system from an overvoltage fault condition. This OVP point can be programmed through the use of external resistors (R8 and R9 in Figure 1). A reference value of 1.245V is used for the OVP. Equation 3 can be used to calculate the resistor value for R9 to set the OVP point. Eq. (3) 1 ) 245 . 1 / ( 8 9 − = OVP V R R LED Dimming The MIC323x family of LED drivers can control the brightness of the LED string via the use of pulse width modulated (PWM) dimming. A PWM input signal of up to 500Hz can be applied to the PWM DIM pin (see Figure 1) to pulse the LED string ON and OFF. It is recommended to use PWM dimming signals above 120Hz to avoid any recognizable flicker by the human eye. PWM dimming is the preferred way to dim a LED in order to prevent color/wavelength shifting, as occurs with analog dimming. The output current level remains constant during each PWMD pulse. Oscillator and Switching Frequency Selection The MIC323x family features an internal oscillator that synchronizes all of the switching circuits internal to the IC. This frequency is adjustable on the MIC3230 and MIC3231 and fixed at 400kHz in the MIC3232. In the MIC3230/1, the switching frequency can be set by choosing the appropriate value for the resistor, R1 according to Equation 4: Eq. (4) 035 . 1 ) ( 7526 ) ( ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = Ω kHz F k R SW FS SYNC (MIC3230 Only) Multiple MIC3230 ICs can be synchronized by connecting their SYNC pins together. When synchronized, the MIC3230 with the highest frequency (master) will override the other MIC3230s (slaves). The internal oscillator of the master IC will override the oscillator of the slave part(s) and all MIC3230 will be synchronized to the same master switching frequency. The SYNC pin is designed to be used only by other MIC3230s and is available on the MIC3230 only. If the SYNC pin is being unused, it is to be left floating (open). In the MIC3231, the SYNC pin is to be left floating (open). |
Similar Part No. - MIC3230 |
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Similar Description - MIC3230 |
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