ISL97682IRTZ-TK Intersil, ISL97682IRTZ-TK Datasheet - Page 15

• Manufacturer Part Number: ISL97682IRTZ-TK
• Description: 2 Channel LED Driver, 16LD TQFN 3X3, 1K T&R
• Manufacturer: Intersil
• Series: -r

Specifications of ISL97682IRTZ-TK

• Constant Current: -
• Constant Voltage: -
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: -
• Frequency: 500kHz ~ 650kHz, 900kHz ~ 1.1MHz
• Voltage - Supply: 4 V ~ 26.5 V
• Voltage - Output: 45V
• Mounting Type: Surface Mount
• Package / Case: 16-WFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Components Selections
According to the inductor Voltage-Second Balance principle, the
change of inductor current during the switching regulator
On-time is equal to the change of inductor current during the
switching regulator Off-time. Since the voltage across an inductor
is as shown in Equation 10:
and ΔI
where D is the switching duty cycle defined by the turn-on time
over the switching periods. V
voltage that can be neglected for approximation.
Rearranging the terms without accounting for V
ratio and duty cycle as Equations 12 and 13:
Input Capacitor
Switching regulators require input capacitors to deliver peak
charging current and to reduce the impedance of the input
supply. This reduces interaction between the regulator and input
supply, thereby improving system stability. The high switching
frequency of the loop causes almost all ripple current to flow in
the input capacitor, which must be rated accordingly.
A capacitor with low internal series resistance should be chosen
to minimize heating effects and improve system efficiency, such
as X5R or X7R ceramic capacitors, which offer small size and a
lower value of temperature and voltage coefficient compared to
other ceramic capacitors.
It is recommended that an input capacitor of at least 10µF be
used. Ensure the voltage rating of the input capacitor is suitable
to handle the full supply range.
Inductor
The selection of the inductor should be based on its maximum
and saturation current (I
(DCR), EMI susceptibility (shielded vs unshielded), and size.
Inductor type and value influence many key parameters,
V
V (
V
D
L
O
I
=
⁄
=
–
V
(
0 ) L ⁄
I
L ΔI
V
L
=
O
×
@ On = ΔI
1
–
⁄
×
V
L
(
I
1 D
D
⁄
) V
Δt
–
⁄
×
t
O
S
)
=
L
@ Off, therefore:
(
V
O
–
SAT
V
D
) characteristics, power dissipation
–
D
V
15
is a Schottky diode forward
I
)
⁄
L
×
1 (
ISL97682, ISL97683, ISL97684
–
D )
×
t
S
D
gives the boost
(EQ. 10)
(EQ. 11)
(EQ. 12)
(EQ. 13)
IL
including ripple current, current limit, efficiency, transient
performance and stability.
The inductor’s maximum current capability must be adequate
enough to handle the peak current at the worst case condition.
Additionally if an inductor core is chosen with too low a current
rating, saturation in the core will cause the effective inductor
value to fall, leading to an increase in peak to average current
level, poor efficiency and overheating in the core. The series
resistance, DCR, within the inductor causes conduction loss and
heat dissipation. A shielded inductor is usually more suitable for
EMI susceptible applications, such as LED backlighting.
The peak current can be derived from the voltage across the
inductor during the Off-period, expressed in Equation 14:
The choice of 85% is just an average term for the efficiency
approximation. The first term is the average current, which is
inversely proportional to the input voltage. The second term is
the inductor current change, which is inversely proportional to L
and F
Applications
Low Voltage Operations
The ISL97682, ISL97683, ISL97684 VIN pin can be separately
biased from the LEDs power input to allow low voltage operation.
For systems that have only single supply, VOUT can be tied to the
driver VIN pin to allow initial start-up; see Figure 26. The circuit
works as follows; when the input voltage is available and the
device is not enabled, the V
voltage drop. The V
start-up once the part is enabled. Once the driver starts up with
V
As long as the V
loss on VIN is acceptable, this configuration can be used for input
voltage as low as 3.0V. For systems where a single input supply
of 4V to 5.5V is available, the VIN pin can be shorted to VDC,
allowing a slight gain in efficiency due to bypassing the internal
LDO.
For systems that have dual supplies, the VIN pin can be biased
from 5V to 12V. The input voltage can be as low as 2.7V without
the limitations previously mentioned; see Figure 27.
OUT
peak
regulating to the target, the VIN pin voltage also increases.
SW
=
(
as a result, for a given switching.
V
O
×
I
O
OUT
)
⁄
(
OUT
85%
does not exceed 26.5V and the extra power
bootstrapped to VIN pin allows an initial
×
V
I
OUT
)
+
1 2 V
follows V
⁄
[
I
×
(
IN
V
O
with a Schottky diode
–
V
I
)
⁄
L (
×
March 11, 2011
V
O
×
FN7689.0
(EQ. 14)
f
SW
)
]