MAX16809EVKIT+ Maxim Integrated Products, MAX16809EVKIT+ Datasheet - Page 7

• Manufacturer Part Number: MAX16809EVKIT+
• Description: Power Management Modules & Development Tools EVAL KIT FOR MAX16809
• Manufacturer: Maxim Integrated Products

Specifications of MAX16809EVKIT+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The amplitude of the output sink currents for all 16
channels is set to the same value by the resistor (R1)
from the SET pin to ground. The minimum allowed
value of R
55mA. The maximum allowed value of R
MAX16809 EV kit uses 430Ω for R
output current to 40mA. To set a different output cur-
rent, use the following equation:
where R
ohms and I
To reduce power dissipation in the IC, the MAX16809
EV kit features adaptive control of VLED based on the
operating voltage of the LED strings. The constant-cur-
rent-sink outputs can sink stable currents with output
voltages as low as 0.8V. The voltage at each of the 16
outputs will be the difference between VLED and the
total forward voltage of the LED string connected to
that output. The MAX16809 EV kit implements a feed-
back mechanism to sense the voltage at each of the 16
constant-current-sink outputs. Using dual zener diodes
(D3–D10), the MAX16809 EV kit selects the lowest dri-
ver voltage (with the greatest LED string voltage) to
regulate. The boost-converter PWM then adjusts so that
VLED is high enough for this sink output to settle to
Figure 1. Inverting PWM Drive Circuit
Adaptive LED Supply Voltage Control
VBIAS
SET
PWM
COMP
SET
OUT
FB
is the current-setting resistor (R1) value in
is 311Ω, which sets the output currents to
is the desired output current in milliamps.
_______________________________________________________________________________________
10pF
C28
R
0.1μF
C30
SET
180kΩ
220pF
Output Current Setting
=
C29
17100
R5
I
OUT
SET
50kΩ
U4B
R11
R15
10kΩ
OEB
, which sets the
3
SET
5
2
is 5kΩ. The
VLED
SN74LVC2G14
4
MAX16809 Evaluation Kit
R2
330kΩ
R6
22kΩ
D12
SDM03U40
approximately 0.8V. All the other strings have sufficient
voltage, as their total forward voltages are lower. The
feedback mechanism ensures that the IC dissipates the
minimum possible power. For adaptive control to func-
tion efficiently connect LED strings to all 16 channels
and use an equal number of LEDs from the same bin in
each string. If some of the 16 channels are not used,
then the zener diodes (D3–D10) should be removed
from the unused channels.
Use the equation below to calculate the value of R2 to
get the required minimum voltage at the sink outputs:
where 2.5V is the feedback reference, V
ward drop of the ORing diode (D3–D10), V
the required sink-output voltage, and V
inal total forward voltage of the LED strings. Select the
value of R2 such that R7 is approximately 10kΩ.
The zener diodes (D3–D10) also provide output over-
voltage protection. If an LED string gets partially or fully
shorted, making the sink-output voltage go high, 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.
When the outputs are off, the LED drivers are at high
impedance and the feedback network now combines
R6 and D12 to provide a path for the feedback current
and to control VLED. Use the following equation to
D1
33V
10.5kΩ
R7
R2 =
OUT0 OUT1
1
(
V
3
FLED
D3
AZ23C15-7
2
2 5
.
+
−
V
V
S
DZ
−
2 5
−
. )
V
S
OUT14 OUT15
×
1
R
3 D10
FLED
7
AZ23C15-7
2
DZ
S
is the nom-
is the for-
= 0.5V is
7