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MAX16820EVKIT Dane(HTML) 3 Page - Maxim Integrated Products

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Szczegółowy opis  MAX16820 Evaluation Kit
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MAX16820EVKIT Datasheet(Arkusz danych) 3 Page - Maxim Integrated Products

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Hysteretic Mode
To enter hysteretic mode, the following input require-
ments must be met: set VIN above 5V or above VFLED +
4V (whichever is greater), and provide 1.1A of input cur-
rent to the EV kit. If low-voltage or low-current input con-
ditions fail to meet the input requirements for hysteretic
mode, the MAX16820 controller operates in linear
mode providing DC current to the LED load.
The MAX16820’s DRV pin drives the external MOSFET
(N1) hysteretically. The MAX16820 drives N1 until the
LED current reaches the upper current-sense threshold.
At that point, the controller disables N1 until the LED cur-
rent reaches the lower current-sense threshold. The LED
current will continuously ripple between ±8% of ILED
(1A). To disable the DRV output, set VIN below 4.5V
when VIN is falling or install a shunt on jumper JU1.
Output Current Setting
In hysteretic mode, the MAX16820 EV kit circuit’s aver-
age LED current (ILED) is configured to 1A by sense
resistor R1. See the equation below to design for a dif-
ferent ILED and for selecting a new resistor value. If
designing for a higher ILED, verify that the new current
setting does not exceed the power rating of compo-
nents R1, L1, N1, and D1. See the
Selection section for more information:
where ILED = desired average LED current, VSNSHI
(210mV) is the MAX16820’s upper-sense-voltage
threshold, and VSNSLO (190mV) is the MAX16820’s
lower-sense-voltage threshold.
Component Selection
Use the MAX16820 Design Calculator, available at, to make prop-
er component selections for custom designs and to
determine the associated LED ripple current. Increase
the value of inductor L1 to decrease ripple current.
When prompted by the Design Calculator, the forward
voltage of freewheel diode D1 is 0.5V.
LED Ripple Current
Typically, the LED ripple current equals the inductor rip-
ple current. To reduce the LED ripple current, install
optional output capacitor C3. The EV kit provides surface-
mount 0603 pads for a capacitor nominal value of 0.1µF.
LED Dimming
The MAX16820 EV kit features a DIM input PCB pad
that can be used for controlling LED brightness.
Remove the shunt on jumper JU1 (Table 1). Connect a
digital PWM signal with a 2.8V to VIN logic level and a
switching frequency between 100Hz and 20kHz.
Frequencies lower than 100Hz can introduce flickering
in the light output. Vary the duty cycle to adjust the
LED brightness. LED brightness increases when the
duty cycle increases and vice versa. When the PWM
signal’s duty cycle is 100%, the LEDs are fully on.
Evaluating the MAX16819
The MAX16820 EV kit can also evaluate the MAX16819
controller by replacing IC U1.
Contact the following number for a free sample of the
MAX16819ATT+. Maxim samples: 800-998-8800.
MAX16820 Evaluation Kit

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