The MAX16801A/B and MAXl6802A/B use a constant current to drive the HB LEDs in general lighting and display applications to provide the required control. The MAX16801A/B is suitable for general purpose AC input LED drivers , while the MAX16802A/B is specified for low voltage (10.8 to 24 V) DC input LED drivers . The HB LED driver circuit control IC consisting of MAX16801A/B and MAX16802A/B is mainly used in LCD TV and LCD monitor RGB backlighting, commercial and industrial lighting , decoration and construction.
1, the main features
The main features of the MAX16801A/8 and MAX16802A/8 are as follows:
Suitable for use as a Buck, Boost, Flyback, SEPIC and other circuit topologies; output power up to 50 W or more; internal error amplifier with 1% accuracy; PWM or linear dimming; 262 kHz (1±12%) fixed switching frequency operation; provides thermal shutdown and digital soft-start, programmable input startup voltage; startup supply current is typically 45μA, operating supply current is typically 1.4 mA; thin 8-pin μMAX Package.
2, pin function and internal structure
The pinouts of the MAX16801A/B and MAX16802A/B are shown in Figure 1. The notes list the functions for their individual pins. The MAX16801A/B and MAX16802A/B integrate a 1.23 V bandgap reference, digital soft-start, UVLO, voltage regulator, 262 kHz oscillator, error amplifier, CPWM comparator, current limit comparator, thermal shutdown, and MOS gate Unit circuit such as driver, as shown in Figure 2
Figure 1 Pin Arrangement
Note: Pin 1: External Programmable Undervoltage Lockout (UVLO), UVLO programming input enable voltage; this pin ground IC enable
Pin 2: Low Frequency PWM Dimming Input / Error Amplifying Inverter Input
Pin 3: Error amplifier output; this pin is connected to the DIM/FB compensation component in high-frequency precision LED current regulation.
Pin 4: current-regulated current sensing terminal, to eliminate the leading edge spike, the upper end of the sensing resistor is connected to an RC filter
Pin 5: Power Ground
Pin 6: Connect the external N-channel MOSFET gate
Pin 7: Gate drive power supply, connect a 10uF decoupling capacitor to GND
Pin 8: IC power supply application terminal, connect a decoupling capacitor of not less than 10uF to GND
Figure 2 Internal structure of the MAX16801A/B and MAX16802A/B
3, application circuit and working principle
3.1 Offline non-isolated flyback LED driver using MAX16801
Figure 3 Offline non-isolated flyback HB LED driver circuit with MAX16801
Offline isolated regression LED driver circuit with programmable input start-up voltage
3.1.1 Input Startup Circuit
The wake-up threshold of the MAX16801 pin UVLO/EN is 1.28 V. The voltage on this pin is only 1.28 V and the circuit can start working. Resistor dividers (R2 and R3) can be used as programming input startup voltages.
The MAX16801 has a built-in bootstrap UVLO circuit with large hysteresis that is useful for designing high-voltage HB LED drivers. When VIN exceeds the threshold level of 23.6 V, the circuit starts. During startup, the UVLO circuit keeps the CPWM comparator, ILIM comparator, oscillator, and output driver off to reduce current consumption. Once VIN reaches 23.6 V, the CPWM and ILIM comparators and oscillators are turned on and the output driver switches are allowed. If VIN drops below 9.7 V, the comparator, oscillator, and output driver are turned off.
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