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MAX16834 Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX16834 Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 23 page MAX16834 High-Power LED Driver with Integrated High-Side LED Current Sense and PWM Dimming MOSFET Driver Maxim Integrated | 9 www.maximintegrated.com The MAX16834 is also suitable for DC-DC converter applications such as boost or boost-buck (Figures 6 and 7). Other applications include boost LED drivers with automotive load dump protection (Figure 4) and high-side buck LED drivers (Figure 5). Undervoltage Lockout/Enable The MAX16834 features an adjustable UVLO using the enable input (UVEN). Connect UVEN to VIN through a resistive divider to set the UVLO threshold. The MAX16834 is enabled when the VUVEN exceeds the 1.435V (typ) threshold. See the Setting the UVLO Threshold section for more information. UVEN also functions as an enable/disable input to the device. Drive UVEN low to disable the output and high to enable the output. Reference Voltage (REF) The MAX16834 features a 3.7V reference output, REF. REF provides power to most of the internal circuit blocks except for the output drivers and is capable of sourcing 1mA to external circuits. Connect a 0.1μF to 0.22μF ceramic capacitor from REF to SGND. Connect REF to REFI through a resistive divider to set the LED current. Reference Input (REFI) The output current is proportional to the voltage at REFI. Applying an external DC voltage at REFI or using a potentiometer from REF to SGND allows analog dim- ming of the output current. High-Side Reference Voltage Input (LV) LV is a reference input. Connect LV to SGND for boost and SEPIC topologies. Connect LV to IN for boost-buck and high-side buck topologies. Dimming Driver Regulator Input Voltage (HV) The voltage at HV provides the input voltage for the dimming driver regulator. For boost or SEPIC topology, connect HV either to IN or to VCC. For boost-buck, con- nect HV to a voltage higher than IN. The voltage at HV must not exceed 28V with respect to PGND. For the high-side buck, connect HV to IN. Dimming MOSFET Driver (DIMOUT) The MAX16834 requires an external n-channel MOSFET for PWM dimming. Connect the gate of the MOSFET to the output of the dimming driver, DIMOUT, for normal operation. The dimming driver is capable of sinking or sourcing up to 50mA of current. n-Channel MOSFET Switch Driver (NDRV) The MAX16834 drives an external n-channel switching MOSFET. NDRV swings between VCC and PGND. NDRV is capable of sinking/sourcing 3A of peak current, allowing the MAX16834 to switch MOSFETs in high- power applications. The average current demanded from the supply to drive the external MOSFET depends on the total gate charge (QG) and the operating frequency of the converter, fSW. Use the following equa- tion to calculate the driver supply current INDRV required for the switching MOSFET: INDRV = QG x fSW Pulse Dimming Inputs (PWMDIM) The MAX16834 offers a dimming input (PWMDIM) for pulse-width modulating the output current. PWM dim- ming can be achieved by driving PWMDIM with a pul- sating voltage source. When the voltage at PWMDIM is greater than 1.435V, the PWM dimming MOSFET turns on and when the voltage on PWMDIM is below 1.235V, the PWM dimming MOSFET turns off. High-Side Linear Regulator (VCLV) The MAX16834’s 5V high-side regulator (CLV) powers up the dimming MOSFET driver. VCLV is measured with respect to LV and sources up to 2mA of current. Bypass CLV to LV with a 0.1μF to 1μF low-ESR ceramic capacitor. The maximum voltage on CLV with respect to PGND must not exceed 28V. This limits the input volt- age for boost-buck topology. Low-Side Linear Regulator (VCC) The MAX16834’s 7V low-side linear regulator (VCC) pow- ers up the switching MOSFET driver with sourcing capa- bility of up to 50mA. Use at least a 1μF low-ESR ceramic capacitor from VCC to PGND for stable operation. LED Current-Sense Input (SENSE+) The differential voltage from SENSE+ to LV is fed to an internal current-sense amplifier. This amplified signal is then connected to the negative input of the transcon- ductance error amplifier. The voltage gain factor of this amplifier is 9.9 (typ). Whenever VLV is greater than 5V, the input impedance of the LED current-sense amplifier seen at the SENSE+ pin is 1k Ω ±30%. In that condition, a bias current of 20μA (±30%) is pulled from SENSE+, in addition to the current due to the 1k Ω resistor. When VLV is less than 1V, the amplifier input (SENSE+ pin) is in high imped- ance and the bias current of 20μA (±30%) is pushed out of that pin. Always have a bypass capacitor of at least 0.1μF value between SENSE+ and LV and close to the IC. |
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