ISL97672AIRZ Intersil, ISL97672AIRZ Datasheet - Page 14

• Manufacturer Part Number: ISL97672AIRZ
• Description: 6-Ch LED Driver With PWM Dimming. Vsc 7.5V Min
• Manufacturer: Intersil
• Series: -r

Specifications of ISL97672AIRZ

• Constant Current: -
• Constant Voltage: -
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: -
• Frequency: 200kHz ~ 1.5MHz
• Voltage - Supply: 4.5 V ~ 26.5 V
• Voltage - Output: 45V
• Mounting Type: Surface Mount
• Package / Case: 20-VFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

current change that is inversely proportional to L and f
result, for a given switching frequency and minimum input
voltage at which the system operates, the inductor I
chosen carefully. Usually, at a given inductor size, 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 ISL97672A current limit may also
have to be considered.
Output Capacitors
The output capacitor smooths 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
due to flow through the ESR of the output capacitor. The ripple
voltage can be shown as Equation 11:
The conservation of charge principle shown in Equation 9 also
indicates that, during the boost switch Off period, the output
capacitor is charged with the inductor ripple current, minus a
relatively small output current in boost topology. As a result, the
user must select an output capacitor with low ESR and adequate
input ripple current capability.
Output Ripple
The value of ΔV
using small ESR capacitors. In general, ceramic capacitors are
the best choice for output capacitors in small- to medium-sized
LCD backlight applications, due to their cost, form factor, and low
ESR.
A larger output capacitor also eases driver response during the
PWM dimming Off period, due to the longer sample and hold
effect of the output drooping. The driver does not need to boost
harder in the next On period that minimizes transient current.
The output capacitor is also needed for compensation, and in
general, 2x4.7µF/50V ceramic capacitors are suitable for
notebook display backlight applications.
Schottky Diode
A high-speed rectifier diode is necessary to prevent excessive
voltage overshoot, especially in the boost configuration. Schottky
diodes are the preferred choice because of their low forward
voltage and reverse leakage current, which minimize losses.
Although the Schottky diode turns on only during the boost
switch Off period, it carries the same peak current as the
inductor, and therefore, a suitable current-rated Schottky diode
must be used.
Applications
High-Current Applications
Each channel of the ISL97672A can support up to 30mA. For
applications that need higher current, multiple channels can be
grouped to achieve the desired current (Figure 23). For example,
the cathode of the last LED can be connected to CH0 through
CH2; this configuration can be treated as a single string with
90mA current driving capability.
ΔV
CO
=
I (
O
⁄
C
O
Co
×
D f
can be reduced by increasing C
⁄
LPEAK
S
)
+
(
I (
during FET On and the voltage drop
O
×
14
ESR
)
O
or f
SAT
S
S
. As a
must be
, or by
ISL97672A
(EQ. 11)
Low-Voltage Operations
The ISL97672A VIN pin can be separately biased from the LED
power input to allow low-voltage operation. For systems that have
only a single supply, V
initial start-up (Figure 24). The circuit works as follows: when the
input voltage is available and the device is not enabled, V
follows V
strapped to the VIN pin allows initial start-up, once the part is
enabled. Once the driver starts up with V
target, the VIN pin voltage also increases. As long as V
not exceed 26.5V and the extra power loss on V
this configuration can be used for input voltage as low as 3.0V.
The Fault Protection FET feature cannot be used in this
configuration.
For systems that have dual supplies, the VIN pin can be biased
from 5V to 12V, while input voltage can be as low as 2.7V
(Figure 25). In this configuration, VBIAS must be greater than or
equal to VIN to use the fault FET.
FIGURE 23. GROUPING MULTIPLE CHANNELS FOR HIGH CURRENT
V
IN
IN
= 3.0V~21V
FIGURE 24. SINGLE SUPPLY 3.0V OPERATION
with a Schottky diode voltage drop. The V
APPLICATIONS
17
1
2
4
6
5
3
8
9
FAULT
VIN
VDC
/FLAG
PWM
EN
RSET
FSW
AGND
ISL97672A
OUT
CH0
CH1
CH2
can be tied to the driver VIN pin to allow
COMP
PGND 19
OVP
CH0
CH1
CH2
CH3
CH4
CH5
LX 20
16
10
11
12
13
14
15
18
V
OUT
OUT
26.5V, 6 x 50mA*
regulating to the
IN
*VIN > 12V
is acceptable,
OUT
OUT
May 2, 2011
boot-
OUT
FN7710.2
does