MAX16812 Maxim Integrated Products, MAX16812 Datasheet - Page 15

• Manufacturer Part Number: MAX16812
• Description: Integrated High-Voltage LED Driver
• Manufacturer: Maxim Integrated Products

The minimum required inductance is a function of the
operating frequency, the input-to-output voltage differ-
ential and the peak-to-peak inductor current (∆I
Higher ∆I
lower ∆I
inductor value minimizes size and cost, improves large-
signal transient response, but reduces efficiency due to
higher peak currents and higher peak-to-peak output
ripple voltage for the same output capacitor. On the
other hand, higher inductance increases efficiency by
reducing the ripple current, ∆I
losses due to the extra turns can exceed the benefit
gained from lower ripple current levels, especially when
the inductance is increased without allowing for larger
inductor dimensions. A good compromise is to choose
∆I
saturating current specification is also important to
avoid runaway current during output overload and con-
tinuous short-circuit conditions.
Buck Configuration: In a buck configuration (Figure
13), the average inductor current does not vary with the
input. The worst-case peak current occurs at the high-
est input voltage. In this case, the inductance, L, for
continuous conduction mode is given by:
Figure 12. Dimming MOSFET Protection
L
equal to 30% of the full load current. The inductor
L
L
requires a higher inductor value. A lower
L
allows for a lower inductor value while a
=
V
______________________________________________________________________________________
OUT
V
TO L_REG PIN
OF MAX16812
with Analog and PWM Dimming Control
INMAX
x V
(
INMAX
x f
Integrated High-Voltage LED Driver
SW
Inductor Selection
L
. However, resistive
−
x I
∆
V
OUT
L
)
GND
GND
V
CC
L
).
MAX6501
where V
switching frequency, and V
Boost Configuration: In the boost converter, the aver-
age inductor current varies with the input voltage and
the maximum average current occurs at the lowest
input voltage. For the boost converter, the average
inductor current is equal to the input current. In this
case, the inductance, L, is calculated as:
where V
output voltage, and f
Figure 14.
Buck-Boost Configuration: In a buck-boost converter
(see the Typical Application Circuit ), the average
inductor current is equal to the sum of the input current
and the LED current. In this case, the inductance, L, is:
where V
output voltage, and f
4.7µF
TOVER
INMIN
INMIN
INMAX
L
L
=
=
is the minimum input voltage, V
is the minimum input voltage, V
is the maximum input voltage, f
(
V
V
V
IN
OUT
INMIN
100kΩ
5.1V
ZENER
SW
SW
V
V
+
O
OUT
is the switching frequency.
is the switching frequency. See
x V
UT
V
(
INMIN
TO EN PIN OF
MAX16812
OUT
OUT
x f
x V
SW
INMIN
is the output voltage.
)
−
x f
www.DataSheet4U.com
x I
∆
SW
V
INMIN
L
x I
∆
L
)
OUT
OUT
SW
is the
is the
is the
15