MAX16821BEVKIT+ Maxim Integrated Products, MAX16821BEVKIT+ Datasheet - Page 12

• Manufacturer Part Number: MAX16821BEVKIT+
• Description: KIT EVAL FOR MAX16821B
• Manufacturer: Maxim Integrated Products

Specifications of MAX16821BEVKIT+

• Current - Output / Channel: 660mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 28V
• Features: Dimmable
• Voltage - Input: 7 ~ 24V
• Utilized Ic / Part: MAX16821
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
The VEA sets the gain of the voltage control loop, and
determines the error between the differential amplifier
output and the internal reference voltage. The VEA out-
put clamps to 0.93V relative to the internal common-
mode voltage, V
mum current. The maximum average current-limit
threshold is equal to the maximum clamp voltage of the
VEA divided by the gain (34.5) of the current-sense
amplifier. This results in accurate settings for the aver-
age maximum current.
The high-side (DH) and low-side (DL) drivers drive the
gates of external n-channel MOSFETs. The drivers’ 4A
peak sink- and source-current capability provides
ample drive for the fast rise and fall times of the switch-
ing MOSFETs. Faster rise and fall times result in
reduced cross-conduction losses. Size the high-side
and low-side MOSFETs to handle the peak and RMS
currents during overload conditions. The driver block
also includes a logic circuit that provides an adaptive
nonoverlap time to prevent shoot-through currents dur-
ing transition. The typical nonoverlap time is 35ns
between the high-side and low-side MOSFETs.
The MAX16821A/MAX16821B/MAX16821C provide
power to the low-side and high-side MOSFET drivers
through V
vides the additional boost voltage necessary for the
high-side driver. V
low-side driver. Connect a 0.47µF low-ESR ceramic
capacitor between BST and LX and a Schottky diode
from BST to V
The MAX16821A/MAX16821B/MAX16821C include out-
put overvoltage protection (OVP). During fault condi-
tions when the load goes to high impedance (output
opens), the controller attempts to maintain LED current.
The OVP disables the MAX16821A/MAX16821B/
MAX16821C whenever the output voltage exceeds the
OVP threshold, protecting the external circuits from
undesirable voltages.
12
______________________________________________________________________________________
DD
. A bootstrap capacitor from BST to LX pro-
DD
.
CM
Voltage-Error Amplifier (VEA)
DD
(+0.6V), limiting the average maxi-
supplies power internally to the
MOSFET Gate Drivers
Protection
BST
The error amplifier (VEA) output is clamped between
-0.050V and +0.93V with respect to common-mode
voltage (V
average current sourced by the converter during a fault
condition. When a fault condition occurs, the VEA out-
put clamps to +0.93V with respect to the common-
mode voltage (0.6V) to limit the maximum current
sourced by the converter to I
The OVP comparator compares the OVI input to the
overvoltage threshold. The overvoltage threshold is typ-
ically 1.127 times the internal 0.6V reference voltage
plus V
comparator output turning off both high-side and low-
side MOSFETs. Add an RC delay to reduce the sensi-
tivity of the overvoltage circuit and avoid unnecessary
tripping of the converter (Figure 4). After the OVI volt-
age falls below 1.076V (typ.), high-side and low-side
drivers turn on only after a 2048 clock-cycle POR and a
1024 clock-cycle soft-start have elapsed. Disable the
overvoltage function by connecting OVI to SGND.
Figure 4. Overvoltage Protection Input Delay
CM
(0.6V). A detected overvoltage event trips the
CM
MAX16821C
). Average current-mode control limits the
MAX16821A
MAX16821B
EAOUT
DIFF
EAN
OVI
Overvoltage Protection
LIMIT
RB
= 0.0275 / R
R
F
C
RA
OVI
Current Limit
R
S
IN
V
.
OUT