First, MAX16800 performance introduction
The MAX16800 is a high-brightness white LED driver that operates from a high-voltage, constant-current output. The main features of the device: operating voltage range 6.5 ~ 40V; constant current output range 35 ~ 350mA; output current accuracy of up to ± 3.5%; internal integration of low-dropout constant current adjustment tube, the typical differential pressure is 0.5V; Output 5V, 4mA linear regulator to supply internal circuit; overheat shutdown protection; external current sense resistor and internal differential current sense amplifier to form a control loop to stabilize the led current; EN terminal for strobe and input PWM signal Dimming (When connected to a low level, the typical power consumption is 12μA); the small size has a 16-pin TQFN package with enhanced heat dissipation; the operating temperature range is -40 to +125°C.
The internal block diagram of the MAX16800 is shown in Figure 1. It consists of a differential current sense amplifier (external current sense resistor RSENSE), error amplifier, MOSFET driver, trim tube (N-channel power MOSFET), reference voltage source, 5V linear regulated power supply, enable (chip select) control circuit And the overheat shutdown protection circuit is composed.
Figure 1 Block diagram of the MAX16800
In the figure, CIN and COUT are the input and output capacitors of the 5V linear regulator. LEDs 1, LED2, ..., LEDN is the load, and RSENSE is the current sense resistor. (When the load current ILED flows through RSENSE, it is generated at both ends of CS+ and CS-. The voltage is proportional to the ILED, which is detected by the input current.
Second, the working principle
Its working principle: After power-on, if the EN terminal applies a high level, the circuit works, and the corresponding RSENSE value is determined according to the set ILED current. The voltage generated at the RSENSE (ILED × RSENSE) to the CS+, CS- input differential current sense amplifier, its output voltage is proportional to the ILED; this voltage is input to the inverting terminal of the error amplifier, its non-inverting terminal is connected to the reference voltage, the error amplifier The output voltage is driven by a boost MOSFET driver to drive the pass transistor (N-channel MOSFET) so that there is a certain VGS that guarantees the corresponding ID (ie ILED).
If VIN ↓ → ILED ↓ → ILED × RSENSE ↓ → current sense amplifier output voltage ↓ → error amplifier output voltage ↑ → boost MOSFET driver output voltage ↑ → VGS ↑ → ID ↑ (ie ILED ↑). This feedback control loop ensures that the load current ILED is essentially constant, enabling constant current drive of the LED.
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