Maxim Integrated MAX16821B Evaluation Kit MAX16821BEVKIT+ MAX16821BEVKIT+ Data Sheet

The MAX16821B delivers 660mA into an LED string
rated up to a maximum of 28V. Resistor R7 sets the
MAX16821B EV kit LED output current. Use the follow-
ing equation to calculate R7 when reconfiguring the
LED current:

where 100mV is the MAX16821B regulated SENSE+
to SENSE- differential current-sense voltage and I

LED

is

the desired LED current.

Current-sense resistor R6 sets the EV kit’s circuit aver-
age input current limit to 3.75A. During an overload
condition at low line, the MAX16821B regulates the
average input current to 3.75A. Use the following equa-
tion to calculate a new R6 value when reconfiguring the
input current limit:

where I

IN

is the input current limit.

For additional information, refer to the 

Average Current

Limit section in the MAX16821A/MAX16821B/MAX16821C
IC data sheet for setting the input current limit when
configuring the MAX16821B in a boost configuration.

The LED brightness can be dimmed using a PWM sig-
nal with a 5V logic-high level and frequency range of
100Hz to 5kHz. Connect the PWM signal to the
PWMDIM and SGND PCB pads to control the LEDs’
brightness.

The maximum voltage on the LED+ pin is limited to 33V,
with respect to GND, by a resistor feedback network
formed by resistors R1 and R2. When the voltage at

LED+ exceeds the programmed 33V threshold, the
low-side driver turns off to prevent current through the
LED string connected between LED+ and LED-. Use
the following equation to calculate R1 and R2 resistor
values for a new overvoltage threshold:

where V

OV_LIM

is the desired overvoltage threshold, R2

is typically 10kΩ, and V

OV

is 1.276V.

The MAX16821B EV kit switching frequency (f

SW

) is

configured to 500kHz by resistor R4. To reconfigure the
MAX16821B switching frequency from 125kHz to
1.5MHz, use the equations below to calculate the new
value for R4:

where f

SW 

is the desired switching frequency.

When reconfiguring the MAX16821B EV kit switching
frequency, other components may need to be changed
for proper stable operation.

The MAX16821B EV kit also features a clock output sig-
nal that is 180° out-of-phase with respect to MOSFET
N5. The clock output is available at the CLKOUT PCB
pad. Use the SGND PCB pad as a reference ground for
the CLKOUT signal.

The MAX16821B is enabled through pullup resistor R5.
To disable the MAX16821B EV kit, connect the EN PCB
pad to the SGND pad.

R

x

f

for

k

R

k

R

x

f

for

k

R

k

SW

SW

4

6 4

10

40

4

120

4

6 25

10

120

4

500

10

10

 

 

.    

,   

     

 

 

.

 

 

,   

     

=

≤

≤

=

≤

≤

Ω

Ω

Ω

Ω

R

R

V

V

V

OV LIM

OV

OV

1

2

 

 

   

   

_

=

×

−

(

)

R

mV

I

IN

6

26 4

 

 

.

=

R

mV

I

LED

7

100

 

 

=