ISL97635AIRZ Intersil, ISL97635AIRZ Datasheet - Page 24

• Manufacturer Part Number: ISL97635AIRZ
• Description: IC LED DRVR WHT/RGB BCKLGT 24QFN
• Manufacturer: Intersil
• Type: Backlight, White LED, RGBr

Specifications of ISL97635AIRZ

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight
• Type - Secondary: RGB, White LED
• Frequency: 600kHz, 1.2MHz
• Voltage - Supply: 6 V ~ 24 V
• Voltage - Output: 34.5V
• Mounting Type: Surface Mount
• Package / Case: 24-VQFN
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 35mA
• Internal Switch(s): Yes
• Efficiency: 91%
• 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:
and ΔI
where D is the switching duty cycle defined by the turn-on
time over the switching period. V
voltage that can be neglected for approximation.
Rearranging the terms without accounting for V
boost ratio and duty cycle respectively as Equations 18
and 19:
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, 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.
In boost mode, input current flows continuously into the
inductor, with an AC ripple component proportional to the
rate of inductor charging only and smaller value input
capacitors may be used. It is recommended that an input
capacitor of at least 10µF be used. Ensure the voltage rating
V
(
V
D
V
RESERVED RESERVED
L
O
Bit 7 (R/W)
I
=
–
⁄
=
REGISTER 0x09
V
(
0 ) L ⁄
BIT ASSIGNMENT
V
L
I
L
=
O
×
@ On = ΔI
1
ΔI
–
×
⁄
CH[5..0]
V
L
(
D
1 D
I
⁄
) V
Δt
×
–
⁄
Bit 6 (R/W)
t
S
O
)
=
L
(
@ Off, therefore:
V
O
–
V
D
Bit 5 (R/W)
OUTPUT CHANNEL REGISTER
–
24
V
CH5
I
CH5 = Channel 5, CH4 = Channel 4 and so on
)
D
⁄
L
is Schottky diode forward
×
1 (
–
Bit 4 (R/W)
BIT FIELD DEFINITIONS
D )
CH4
FIGURE 29. OUTPUT CHANNEL REGISTER
×
t
S
D
gives the
(EQ. 16)
(EQ. 17)
(EQ. 18)
(EQ. 19)
Bit 3 (R/W)
CH3
ISL97635A
Bit 2 (R/W)
IL
CH2
of the input capacitor is suitable to handle the full supply
range.
Inductor
The selection of the inductor should be based on its
maximum current (I
(DCR), EMI susceptibility (shielded vs unshielded), and size.
Inductor type and value influence many key parameters,
including ripple current, current limit, efficiency, transient
performance and stability.
Its maximum current capability must be adequate to handle
the peak current at the worst case condition. 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 fact that the
voltage across the inductor during the Off-period can be
shown as Equation 20:
The choice of 85% is just an average term for the efficiency
approximation. The first term is average current that is
inversely proportional to the input voltage. The second term
is inductor current change that is inversely proportional to L
and f
minimum input voltage the system operates, the inductor
I
usually the larger the inductance, the higher the series
resistance because of the extra winding of the coil. Thus, the
higher the inductance, the lower the peak current capability.
The ISL97635A current limit may also have to be taken into
account.
Output Capacitors
The output capacitor acts to smooth the output voltage and
supplies load current directly during the conduction phase of
the power switch. Output ripple voltage consists of the
discharge of the output capacitor for I
SAT
peak
must be chosen carefully. At a given inductor size,
S
=
. As a result, for a given switching frequency and
(
V
Bit 1 (R/W)
O
×
CH1
I
O
)
⁄
(
85%
SAT
Bit 0 (R/W)
) characteristics, power dissipation
×
V
CH0
I
)
+
1 2 V
⁄
[
I
LPEAK
×
(
V
O
–
during FET On
V
I
December 22, 2008
)
⁄
L (
×
V
FN6564.2
(EQ. 20)
O
×
f
S
)
]