MAX16812EVKIT+ Maxim Integrated, MAX16812EVKIT+ Datasheet - Page 4

• Manufacturer Part Number: MAX16812EVKIT+
• Description: LED Lighting Development Tools Evaluation Kit for the MAX16812
• Manufacturer: Maxim Integrated
• Series: MAX16812r

Specifications of MAX16812EVKIT+

• Product: Evaluation Kits

PWM dimming is achieved by turning on and off the
MOSFET (N1) in series with the LED string. LED dim-
ming is achieved on the MAX16812 EV kit by applying
a digital PWM signal or an analog DC voltage at the
DIM PCB input pad, or by adjusting potentiometer R9.
The voltage at the MAX16812 DIM pin can be adjusted
using potentiometer R9 to control the external LEDs’
brightness. When adjusting the DC voltage using R9,
install a shunt across jumper JU2 and remove the shunt
at jumper JU3. The MAX16812 IC DIM pin voltage can
be monitored by placing a voltmeter across the DIM and
AGND PCB pads. LED dimming can also be accom-
plished by removing the shunt at jumper JU2 and con-
necting an external power source at the DIM PCB pad.
The DC voltage at the DIM PCB pad sets the MAX16812
duty cycle of the driver controlling the gate of the dim-
ming MOSFET (N1), which controls the external LED
brightness.
Use the following equation to calculate the voltage at
the DIM PCB pad, necessary for the N1 dimming FET
output duty cycle (D):
where DIM is the DC voltage at the MAX16812 EV kit
DIM PCB pad in volts and D is the output duty cycle of
the LED current.
To control LED dimming using a PWM signal at the DIM
PCB pad, remove the shunt from jumper JU2 and place
a shunt across jumper JU3. Connect a digital PWM sig-
nal with a 5V TTL or 3.3V CMOS logic level and switch-
ing frequencies up to 2kHz. See Table 2 for jumpers
JU2 and JU3 settings for PWM dimming operation.
MAX16812 Evaluation Kit
Table 2. PWM Dimming Operation
(Jumpers JU2 and JU3)
4
installed
installed
Installed
Installed
SHUNT POSITION
JU2
_______________________________________________________________________________________
Not
Not
Installed
Installed
installed
installed
JU3
Not
Not
DIM ≈ D x 1.24V
adjusted using potentiometer R9
(Jumpers JU2 and JU3)
EV KIT DIMMING OPERATION
Analog DC voltage at DIM pin
PWM Dimming Control
Analog DC voltage applied
PWM signal applied
at DIM PCB pad
at DIM PCB pad
Not applicable
For additional information on operating the MAX16812
EV kit in linear dimming or PWM dimming operation,
refer to the PWM Dimming section in the MAX16812 IC
data sheet.
During PWM dimming, there may be audible noise due
to the piezo effect of the output capacitors connected at
LED+. To alleviate the audible noise, remove ceramic
capacitors C9, C10, and C11, and add electrolytic
capacitors at the C19 and C20 pads. For proper PWM
dimming operation, when using electrolytic capacitors, it
may be required to change some of the compensation
components.
The maximum voltage on the LED+ pin is limited to
54.4V with respect to GND, by a feedback network
formed by resistors R5 and R6. When the voltage at
LED+ exceeds the programmed 54.4V threshold, PWM
switching is terminated and no further energy is trans-
ferred to the load connected between LED+ and LED-.
If the MAX16812 EV kit is turned on with no load, the
voltage at LED+ may rise to unsafe levels. Even
though the EV kit has overvoltage protection, it is rec-
ommended to connect the specified load before pow-
ering up the EV kit. Refer to the Setting the Overvoltage
Threshold section in the MAX16811/MAX16812 IC data
sheet for setting the overvoltage threshold.
Output Overvoltage Protection