ISL97634IRT18Z-T Intersil, ISL97634IRT18Z-T Datasheet - Page 7

• Manufacturer Part Number: ISL97634IRT18Z-T
• Description: IC LED DRIVR WHITE BCKLGT 8-TDFN
• Manufacturer: Intersil
• Type: Backlight, White LEDr

Specifications of ISL97634IRT18Z-T

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight
• Type - Secondary: White LED
• Frequency: 1.3MHz ~ 1.6MHz
• Voltage - Supply: 2.4 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-TDFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 50mA
• Internal Switch(s): Yes
• Efficiency: 85%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

only rated for the required voltage range can therefore be
used, which will optimize the component costs in some cases.
Shutdown
When PWM/EN is taken low the ISL97634 enters into the
power-down mode where the supply current is reduced to
less than 1µA. The device resumes normal when the
PWM/EN goes high.
Components Selection
The input capacitance is typically 0.22µF. The output
capacitor should be in the range of 0.22µF to 1µF. X5R or
X7R type of ceramic capacitors of the appropriate voltage
rating are recommended.
When choosing an inductor, make sure the average and
peak current ratings are adequate by using Equations 3, 4 and
5 (80% efficiency assumed):
Where:
• ΔI
• L is the inductance in H
• f
The ISL97634 supports a wide range of inductance values
(10µH to ~82µH). For lower inductor values or lighter loads,
the boost inductor current may become discontinuous. For
high boost inductor values, the boost inductor current will be
in continuous mode.
In addition to the inductor value and switching frequency, the
input voltage, number of LEDs and the LED current also
affects whether the converter operates in continuous
conduction or discontinuous conduction mode.
Both operating modes are allowed and normal. The
discontinuous conduction mode yields lower efficiency due
to higher peak current.
Δ
ISL97634IRT14Z
ISL97634IRT18Z
ISL97634IRT26Z
I
I
LAVG
LPK
I
L
OSC
=
L
PART NO.
=
is the peak-to-peak inductor current ripple in Amps
V
-------------------------------------------------- -
=
IN
L V
I
is the switching frequency, typically 1.45MHz
LAVG
I
-------------------------------- -
⋅
LED
⋅
0.8 V
(
V
OUT
OUT
+
⋅
⋅
V
1
-- -
2
⋅
OUT
IN
f
⋅
–
OSC
Δ
V
I
L
IN
)
OVP
14V
18V
26V
TABLE 1.
7
MAX NO. OF
LEDS
3
4
7
MAX ILED
70mA
50mA
30mA
(EQ. 3)
(EQ. 4)
(EQ. 5)
ISL97634
Compensation
The product of the output capacitor and the load create a
pole while the inductor creates a right half plane zero. Both
of these attributes degrade the phase margin but the
ISL97634 has internal compensation network that ensures
the device operates reliably under the specified conditions.
The internal compensation and the highly integrated
functions of the ISL97634 make it a design friendly device to
be used in high volume, high reliability applications.
Applications
Analog Dimming
Analog dimming is usually not recommended because of the
brightness non-linearity at low levels dimming. However,
some systems are EMI or noise sensitive that analog
dimming may be more suitable than PWM dimming under
those situations. The ISL97632 is part of the same family as
the ISL97634 and has been designed with a serial interface
to give access to 32 separate dimming levels. Alternatively
analog dimming can be achieved by applying a variable DC
voltage (V
current. As the DC dimming signal voltage increases above
VFB, the voltages drop on R
voltage drop on RSET decreases. Thus, the LED current
decreases as shown in Equation 6:
I
If V
brightness will increase.
The DC dimming signal voltage can be a variable DC voltage
from a POT, a DCP (Digitally Controlled Potentiometer), or a
DC voltage generated by filtering a high frequency PWM
control signal.
As brightness is directly proportional to LED currents, V
may be calculated for any desired “relative brightness” (F)
using Equation 7:
Where F = I
V
LED
Dim
FIGURE 14. ANALOG DIMMING CONTROL APPLICATION
DIM
=
3.3V
=
V
------------------------------------------------------------------------- -
is taken below FB, the inverse will happen and the
V
R
------ - V
R
FB
IN
2
1
Dim
1µF
⋅
⋅
LED
C1
(
R
FB
) at FB pin (see Figure 14) to adjust the LED
CIRCUIT
1
R
(dimmed)/I
+
⋅
2
⎛
⎜
⎝
R
⋅
1
R
2
+
V
PWM
) V
SET
GND
ISL97634
IN
R
------ - F
R
–
1
2
22µH
L1
–
Dim
V
OUT
LED
⎞
⎟
⎠
LX
LX
FB
1
⋅
R
and R
R2
1
(undimmed).
3.3k
2
R1
increase and the
V
Dim
LEDs
R
4.75
SET
Ω
March 7, 2008
C2
0.22µF
FN6264.3
(EQ. 6)
(EQ. 7)
Dim