MAX16833AUE+T Maxim Integrated Products, MAX16833AUE+T Datasheet - Page 18

• Manufacturer Part Number: MAX16833AUE+T
• Description: IC HB LED DVR CURR SENSE 16TSSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX16833AUE+T

• Topology: Flyback, Low Side, PWM, SEPIC, Step-Down (Buck), Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: No
• Type - Primary: Automotive, General Purpose
• Type - Secondary: High Brightness LED (HBLED)
• Frequency: 100kHz ~ 1MHz
• Voltage - Supply: 5 V ~ 65 V
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP (0.173", 4.40mm Width) Exposed pad
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 3A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Details

High-Voltage HB LED Drivers with
Integrated High-Side Current Sense
where IG
MOSFET Q1 in amperes when it is turned on and turned
off, respectively, V
in amperes, f
MOSFET capacitance in farads.
Use a Schottky diode as the rectifier (D1) for fast switch-
ing and to reduce power dissipation. The selected
Schottky diode must have a voltage rating 20% above
the maximum converter output voltage. The maximum
converter output voltage is V
and V
The current rating of the diode should be greater than I
in the following equation:
Select a dimming MOSFET (Q2) with continuous current
rating at the operating temperature higher than the LED
current by 30%. The drain-to-source voltage rating of the
dimming MOSFET must be higher than V
The LED current control loop comprising the switching
converter, the LED current amplifier, and the error ampli-
fier should be compensated for stable control of the LED
current. The switching converter small-signal transfer
function has a right-half-plane (RHP) zero for both boost
and buck-boost configurations as the inductor current
is in continuous conduction mode. The RHP zero adds
a 20dB/decade gain together with a 90-degree phase
lag, which is difficult to compensate. The easiest way
to avoid this zero is to roll off the loop gain to 0dB at a
18
P
_____________________________________________________________________________________
SW
LED
×
=
P
ON



+ V




SW
IG
IL
SW
I
1
ON
AV G
and IG
INMAX
D
×
=



= IL




is in hertz, and C
IG
IL
+
LED
×
IG
1
ON
AV G
AVG
(V
in buck-boost configuration.
OFF
OFF
1
LED
and V
+
×
Feedback Compensation
x (1 - D
IG



V
are the gate currents of the
+
LED
OFF
1
Buck-Boost Configuration
V
INMAX
LED
INMAX
2
2
2



MAX
×
GD
in boost configuration
C
Boost Configuration
are in volts, IL
)
GD
) x 1.5
Dimming MOSFET
2
is the gate-to-drain
×
×
C
Rectifier Diode
LED
f
GD
SW
by 20%.




×
f
SW
AVG




is
D
frequency less than 1/5 the RHP zero frequency with a
-20dB/decade slope.
The worst-case RHP zero frequency (f
lated as follows:
where f
tance value of L1 in henries, and I
The switching converter small-signal transfer function
also has an output pole for both boost and buck-boost
configurations. The effective output impedance that
determines the output pole frequency together with the
output filter capacitance is calculated as follows:
where R
at the operating current in ohms, R7 is the LED current-
sense resistor in ohms, V
amperes.
The output pole frequency for both boost and buck-
boost configurations is calculated as below:
where f
tance in farads, and R
ance in ohms calculated above.
The feedback loop compensation is done by connecting
resistor R10 and capacitor C4 in series from the COMP
pin to GND. R10 is chosen to set the high-frequency
gain of the integrator to set the crossover frequency
R
ZRHP
P2
OUT
LED
R
is in hertz, C
OUT
=
is the dynamic impedance of the LED string
f
f
is in hertz, V
ZRHP
ZRHP
(R
f
P2
LED
=
=
(R
=
=
+
(R
2
OUT
LED
(R
R7) I
2
π ×
V
V
LED
π × ×
OUT
LED
LED
LED
LED
LED
C
×
2
+
is the effective output imped-
L I
OUT
π × ×
Buck-Boost Configuration
R7) I
Buck-Boost Configuration
LED
×
×
+
is the output filter capaci-
+
1
(1- D
is in volts, L is the induc-
is in volts, and I
(1- D
LED
L I
R7) V
×
R7) V
×
×
LED
R
LED
Boost Configuration
Boost Configuration
D
LED
×
×
MAX
MAX
OUT
×
MAX
D
MAX
is in amperes.
LED
+
LED
ZRHP
)
)
V
2
2
LED
+
V
) is calcu-
LED
LED
is in