MAX16807EVKIT+ Maxim Integrated Products, MAX16807EVKIT+ Datasheet - Page 5

• 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

When the outputs are off, the LED drivers are high
impedance and the feedback network now combines
R13 and D6 to provide a path for the feedback current
and to control VLED. Use the following equation to cal-
culate the value of R13 to get the required LED supply
voltage during PWM off time:
where 2.5V is the feedback reference voltage, 0.4V is
the total voltage dropped by diode D6, and VLED
the desired LED supply voltage during PWM off time.
VLED
voltage, plus additional headroom for the LED drivers
that must be greater than 0.8V, as well as a reserve
voltage (about +1V). This reserve voltage allows the
MAX16807 to provide current for very short PWM dim-
ming pulses. With pulses as low as 2µs, the VLED con-
trol loop is not able to react, and the output capacitors
provide all the current. For longer PWM dimming puls-
es, the control loop will react and the supply will oper-
ate at the adaptive voltage level.
During an open LED condition, the 33V zener diode
(D8) limits the maximum VLED supply voltage to 35.5V.
If VLED attempts to increase beyond this level, D8 con-
ducts in reverse direction and pulls the FB pin high,
which causes the boost regulator to cut back on the
PWM signal and reduce the output voltage.
The EV kit boost-converter circuit is configured to gener-
ate up to 33V of LED voltage (VLED) and operate at a
switching frequency of 350kHz in continuous conduction
mode (CCM). The MAX16807’s current-mode PWM con-
troller drives external MOSFET N1. The MOSFET is
turned on at the beginning of every switching cycle and
turned off when the current through the inductor (L1)
reaches the peak value set by the error-amplifier output
voltage. Inductor current is sensed by the MAX16807 CS
pin using the voltage across current-sense resistor R9.
The RC filter, consisting of R5 and C8, removes voltage
spikes in the current-sense signal produced by the turn-
on gate current of MOSFET N1, and the reverse-recov-
ery current of D1. Without filtering, these current spikes
can cause the MAX16807 to turn off N1 prematurely.
The filter time constant is configured to 120ns.
During normal operating conditions, the feedback loop
and compensation network (R1, R10, R11, C6, and C7)
control the peak current. The error amplifier compares
a scaled-down version of the VLED voltage with the
MAX16807 highly accurate 2.5V reference. The error
amplifier and compensation network then amplify the
OFF
should be set to the worst-case LED string V
R13 =
_______________________________________________________________________________________
R10
VLED
×
(
2.5V - 0.4V
OFF
- 2.5V
Boost Converter
)
OFF
is
MAX16807 Evaluation Kit
F
error signal, and the current comparator compares this
signal to the sensed current voltage to create a PWM
drive output.
Initially, decide the input supply voltage range, the max-
imum voltage (VLED) that is required to drive the LED
strings, plus 1V (minimum voltage across the constant-
current sink = 0.8 + VLED ripple peak), and the output
current I
Calculate maximum duty cycle D
equation:
where V
(~0.6V), VIN
this case, 9V), and V
of the MOSFET N1 when it is on.
Select the switching frequency (F
space, noise, dynamic response, and efficiency con-
straints. Select the maximum peak-to-peak ripple on
the inductor current (IL
F
tor current. Use the following equations to calculate the
maximum average inductor current IL
inductor current IL
Since IL
IL
Calculate the minimum inductance value L
inductor current ripple set to the maximum value:
Choose an inductor that has a minimum inductance
that is greater than this calculated value.
Calculate the current-sense resistor (R8 in parallel with
R9) using the equation below:
where 0.3V is the maximum current-sense signal voltage.
The factor 0.75 is for compensating the reduction of
SW
AVG
is 350kHz and IL
:
OUT
D
PP
is the forward drop of the rectifier diode D1
is ±30% of the average inductor current
MIN
L
(the sum of all the LED string currents).
D
MIN
MAX
is the minimum input supply voltage (in
IL
IL
=
PEAK
PEAK
IL
PP
(
R
=
VIN
AVG
CS
FET
VLED V
PP
=
VLED V
:
IL
MIN
PP
=
=
is ±30% of the average induc-
is the drain-to-ground voltage
=
IL
AVG
F
0 3 0 75
). For the MAX16807 EV kit,
SW
1
IL
.
+
AVG
−
Power-Circuit Design
−
+
PEAK
I
×
OUT
V
D
D
×
×
FET
D
MAX
0 3 2
−
+
IL
MAX
.
SW
.
−
VIN
IL
PP
)
V
×
×
2
PP
FET
) depending on the
using the following
D
MIN
MAX
AVG
MIN
and peak
with the
5