Maxim Integrated MAX8790A Evaluation Kit MAX8790AEVKIT+ MAX8790AEVKIT+ Hoja De Datos

The EV kit is populated with two strings of eight WLEDs,
but provides four additional on-board strings to allow
for the evaluation of up to six total strings of eight
WLEDs (48 total WLEDs). In addition, the EV kit can be
used to evaluate external off-board WLED strings, pro-
viding flexibility in the layout of the WLED strings and
allowing for the evaluation of more WLEDs per string.
See the 

White LED String Configuration section for

WLED configuration options.

LED current control is accomplished through either
analog or digital dimming modes, which achieve a
100:1 dimming range. Both dimming modes utilize the
pulse-width modulation (PWM) signal supplied at the
BRT input pad to control the LED current sources. See
the 

LED Dimming Mode section for more details.

As configured, the MAX8790A EV kit operates with a
750kHz switching frequency and an output voltage of
35V. Operating the EV kit at a different switching fre-
quency or output voltage might require component
changes. Refer to the MAX8790A IC data sheet for
details on component selections.

The MAX8790A EV kit can be evaluated with either one
or two input power supplies. When using one input
power supply, connect a 7V to 21V power supply to the
VIN pad and configure jumper JU1 (Table 1) for single-
supply operation. In single-supply operation, do not con-
nect an external power supply or load to the VCC pad.

To utilize two input power supplies, configure jumper
JU1 for dual-supply operation and connect a 4.5V to
5.5V power supply to the VCC pad and a 7V to 21V
power supply to the VIN pad.

SHDN)

The MAX8790A is disabled by connecting 

SHDN to

GND. When in shutdown mode, the IC quiescent cur-
rent is reduced to less than 10µA (typ). The 

SHDN input

is set through jumper JU2. See Table 2 for shutdown
configurations.

The MAX8790A EV kit is configured to operate at
750kHz, but provides the option to set the switching fre-
quency of the step-up DC-DC converter to 500kHz or
1MHz. The switching frequency is set by installing head-
er JU13 and configuring the shunt location as listed in
Table 3. Changing the switching frequency may require
different converter components. Refer to the MAX8790A
IC data sheet for proper component selections.

The full-scale current through each WLED string is con-
figured by connecting ISET (pin 18) to VCC, or by tying
it to GND through resistors R1 and R2. When ISET is
connected to VCC the full-scale current is set to 20mA,
and when pulled to GND the full-scale current is
adjustable from 15mA to 25mA:

where R1 is a 51kΩ resistor and R2 is a 100kΩ poten-
tiometer. The ISET pin is configured through jumper
JU4. See Table 4 for jumper JU4 settings.

 

I

20 x

100k

R1+ R2

LED(FS)

=

⎛
⎝⎜

⎞
⎠⎟

Ω

mA

1-2*

Single (7V to 21V)

2-3

Dual (VIN = 7V to 21V,  VCC = 4.5V

to 5.5V)

*

Default position.

SHDN PIN

Not installed*

Connected to VIN

through R9

Enabled

Installed

Connected to GND

Disabled

*

Default position.

1-2

Connected to VCC

1MHz

2-3

Connected to GND

500kHz

Not installed*

Unconnected

750kHz

*

Default position.