ISL97651ARTZ-TK Intersil, ISL97651ARTZ-TK Datasheet - Page 13

• Manufacturer Part Number: ISL97651ARTZ-TK
• Description: IC LCD SUPPLY HP 4CHN 36-TQFN
• Manufacturer: Intersil

Specifications of ISL97651ARTZ-TK

• Applications: LCD TV/Monitor
• Current - Supply: 400µA
• Voltage - Supply: 4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 36-TQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Buck Converter
The buck converter is the step down converter, which
supplies the current to the logic circuit of the LCD system.
The ISL97651 integrates an 20V N-Channel MOSFET to
save cost and reduce external component count. In the
continuous current mode, the relationship between input
voltage and output voltage is shown in Equation 9:
Where D is the duty cycle of the switching MOSFET.
Because D is always less than 1, the output voltage of buck
converter is lower than input voltage.
The peak current limit of buck converter is set to 2A, which
restricts the maximum output current (average) based on the
Equation 10:
Where ΔI
Equation 11:
Where L is the buck inductor, f
(1.2MHz).
Feedback Resistors
The buck converter output voltage is determined by the
Equation 12:
Where R14 and R15 are the feedback resistors of buck
converter to set the output voltage current drawn by the
resistor network should be limited to maintain the overall
converter efficiency. The maximum value of the resistor
network is limited by the feedback input bias current and the
V
--------------------- -
I
ΔI
V
OMAX
V
FIGURE 12. CASCADED MOSFET TOPOLOGY FOR HIGH
LOGIC
LOGIC
V
pp
IN
IN
=
=
V
--------------------- -
=
=
LOGIC
L f
PP
2A ΔI
⋅
R
-------------------------- -
D
s
14
is the ripple current in the buck inductor as the
–
OUTPUT VOLTAGE APPLICATIONS
R
+
15
INTERSIL
ISL97651
⋅
pp
(
R
1 D
15
–
×
)
V
REF
13
LX1, LX2
s
is the switching frequency
FBB
(EQ. 10)
(EQ. 11)
(EQ. 12)
(EQ. 9)
A
VDD
ISL97651
potential for noise being coupled into the feedback pin. A
resistor network in the order of 1kΩ is recommended.
Buck Converter Input Capacitor
The capacitor should support the maximum AC RMS current
which happens when D = 0.5 and maximum output current.
Where I
shows some recommendations for input capacitor.
Buck Inductor
An inductor value in the range 3.3µH to 10µH is
recommended for the buck converter. Besides the
inductance, the DC resistance and the saturation current
should also be considered when choosing buck inductor.
Low DC resistance can help maintain high efficiency, and the
saturation current rating should be at least 2A. Table 7
shows some recommendations for buck inductor.
Rectifier Diode (Buck Converter)
A Schottky diode is recommended due to fast recovery and
low forward voltage. The reverse voltage rating should be
higher than the maximum input voltage. The peak current
rating is 2A, and the average current should be as the
Equation 14:
Where I
shows some diode recommended.
I
I
4.7µH/2.7A
ACRMS
10µH/2.4A
AVG
PMEG2020EJ
6.8µH/3A
TABLE 6. INPUT CAPACITOR (BUCK) RECOMMENDATION
CAPACITOR
INDUCTOR
TABLE 8. BUCK RECTIFIER DIODE RECOMMENDATION
10µF/16V
10µF/10V
22µF/16V
DIODE
SS22
=
TABLE 7. BUCK INDUCTOR RECOMMENDATION
(
O
O
(
C
1 D
PEAK
is the output current of the buck converter. Table 6
is the output current of buck converter. Table 8
IN
PEAK
–
PEAK
)
)*I
=
o
V
RATING PACKAGE
20V/2A
20V/2A
1210
DIMENSIONS
12.95x9.4x3.0 Coilcraft
R
D
SIZE
1206 TDK
0805 Murata
5.7x5.0x4.7
7.3x6.8x3.2
/I
⋅
AVG
(
(mm)
1 D
–
Murata
VENDOR
SOD323F Philips Semiconductors
)
⋅
I
SMB
O
Murata
TDK
VENDOR
C3216X7R1C106M
GRM21BR61A106K
C3225X7R1C226M
Fairchild Semiconductor
LQH55DN4R7M01K
RLF7030T-6R8M2R8
DO3308P-103
PART NUMBER
PART NUMBER
VENDOR
April 24, 2009
(EQ. 13)
(EQ. 14)
FN7493.3