MAX16807EVKIT+ Maxim Integrated Products, MAX16807EVKIT+ Datasheet - Page 4

• Manufacturer Part Number: MAX16807EVKIT+
• Description: EVAL KIT FOR MAX16807
• Manufacturer: Maxim Integrated Products

Specifications of MAX16807EVKIT+

• Current - Output / Channel: 50mA
• Outputs And Type: 8, Non-Isolated
• Voltage - Output: 32V
• Features: Dimmable
• Voltage - Input: 9 ~ 16V
• Utilized Ic / Part: MAX16807
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX16807 feature an 8-channel constant-current
LED driver, with each channel capable of sinking up to
55mA of LED current. LED strings can be connected
between VLED (J1-1 and J1-2) and the constant-current
sink outputs to drive regulated current through each LED
string. The current through all eight channels is con-
trolled through resistor R7, which is connected from the
SET pin to ground. The current through each string is
configured to 50mA and the maximum VLED voltage to
33V. The EV kit can drive LED strings with a total for-
ward voltage of up to 32V.
The MAX16807 4-wire (DIN, CLK, LE, and OE) serial
interface controls the eight constant-current outputs.
The MAX16807 EV kit circuit connects DIN and LE to
5V and uses a clock signal, generated by inverter U2,
to clock eight logic 1s into the IC’s internal shift regis-
ter, thus enabling all eight channels. The output enable
(OE) pin is configured to provide PWM dimming. An
inverted PWM signal, generated by the inverter U2, drives
the OE pin. When the PWM signal is low (LED drivers off)
it also influences the feedback with the network formed
by R13 and D6. See the Adaptive LED Voltage Control
section for more details.
The amplitude of the output currents for all eight chan-
nels is set by resistor R7. The minimum value for resis-
tor R7 is 324Ω, which sets the output currents to 55mA.
The maximum value of R7 is 4.99kΩ, which sets the
output current to 3.6mA. The MAX16807 EV kit sets the
output current to 50mA with a 365Ω R7 resistor. To set
a different output current, use the following equation:
where I
The MAX16807 EV kit features a PWM input PC pad
that can be used to control the LED brightness by
adjusting the duty cycle of the PWM input signal.
Applying a logic-high signal at the PWM input enables
the output current and a logic-low signal turns off the
output current. The PWM signal is conditioned through
inverter U2 before reaching the MAX16807 OE pin.
Connect a PWM signal with peak amplitude of 3V to 5V
and a frequency in the range of 100Hz to 2kHz to the
MAX16807 Evaluation Kit
4
_______________________________________________________________________________________
OUT
is the desired output current.
R7 =
Output-Current Setting
I
18V
OUT
PWM Dimming
LED Driver
EV kit PWM input PCB pad. Vary the duty cycle to
adjust the LED brightness. The LED brightness increas-
es when the duty cycle increases and vice versa.
The MAX16807 EV kit features a SHDN input PC pad to
enable or disable the MAX16807 IC. Connect 5V or VIN to
the SHDN pad to enable the IC. Connect the SHDN pad
to ground or leave disconnected to disable the IC. The IC
can also be enabled by connecting VIN to test point TP3.
To reduce power dissipation in the IC, the MAX16807
EV kit features adaptive voltage control of VLED based
on the operating voltage of the LED strings. The con-
stant-current outputs can sink stable currents with
channel voltages as low as 0.8V. The voltage at each of
the outputs will be the difference between VLED and
the total forward voltage of the LED string connected to
that output. The MAX16807 EV kit implements a feed-
back mechanism to sense the voltage at each of the
outputs. Using dual zener diodes (D2–D5), the circuit
selects the lowest voltage among all the output chan-
nels. The PWM boost converter will then adjust VLED
until this output channel is 0.8V. All other strings will
have sufficient voltage, as their total forward voltages
are equal or less. This feedback mechanism ensures
that the IC dissipates the minimum possible power. For
adaptive control to function efficiently, connect LED
strings to all eight channels and use equal number of
LEDs of the same V
lowing equation to calculate the value of resistor R10 to
set the minimum voltage at the outputs:
where 2.5V is the feedback reference, V
voltage drop (0.65V) of the zener diodes (D2–D5), VS
(0.8V) is the required sink output voltage, and VF
total nominal operating voltage of the LED strings. Select
the value of R10 such that R12 is approximately 10kΩ.
Zener diodes D2–D5 also provide output overvoltage
protection. If an LED string becomes partially or fully
short-circuited, making the sink output voltage rise
above 17.5V, the 15V zener diode connected to that
output conducts in reverse direction and limits the
VLED voltage. Under this condition, the other LED
strings might not turn on.
R
10
=
Adaptive LED Voltage Control
(
VF
F
2 5
LED
.
rating in each string. Use the fol-
V
−
+
V
VS
DZ
−
−
2 5
VS
.
V
)
×
DZ
R
SHDN Input
12
is the forward
LED
is the