ISL97634IRT26Z-T Intersil, ISL97634IRT26Z-T Datasheet - Page 5

• Manufacturer Part Number: ISL97634IRT26Z-T
• Description: IC LED DRIVR WHITE BCKLGT 8-TDFN
• Manufacturer: Intersil
• Type: Backlight, White LEDr

Specifications of ISL97634IRT26Z-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: 30mA
• Internal Switch(s): Yes
• Efficiency: 85%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

Detailed Description
The ISL97634 uses a constant frequency, current mode
control scheme to provide excellent line and load
regulation. There are three OVP models for driving 3, 4
and 7 LEDs (3.5V/20mA type) and their OVP thresholds
are set at 14V, 18V and 26V respectively. The ISL97634
operates from an input voltage of 2.4V to 5.5V and ambient
temperature from -40°C to +85°C. The switching frequency
is around 1.45MHz and allows the driver circuit to employ
small LC components. The peak forward current of the LED
is set using the R
LED peak current is given by Equation1:
PWM Dimming
The ISL97634’s PWM/EN pin can be tied permanently to
high for a fixed current operation. On the other hand, the
ISL97634 can be applied with an external PWM signal to
I
LED
V
ILED
PWM/EN
FIGURE 7. PWM DIMMING AT 1kHz, D = 1% ZOOM IN
OUT
LX
=
-------------- -
R
V
SET
FB
SET
resistor. In the steady state mode, the
5
R
V
L1 = 22µH
1
IN
FIGURE 9. PWM DIMMING AT 20kHz, D = 50%
= 4 Ω
= 4V
PWM/EN
V
R
L
V
IN
1
1
OUT
= 22µH
= 4Ω
= 4V
(EQ. 1)
ISL97634
ILED
LX
pulse width modulated output current. It is well understood
that the LED brightness is a linear function of the LED
current. In addition, the average LED current corresponds to
the duty cycle “D” of the PWM signal as shown in
Equation 2:
As a result, PWM signal provides a means to dim the LED
brightness. PWM dimming offers the best LEDs matching
over DC dimming. It is because the LED peak current
operating point is far away from the knee of the diode I-V
curve where part to part variations are high. The PWM
dimming test results are shown in Figure 6 with two PWM
frequencies, 1kHz and 20kHz. The vertical scale parameter
FB is proportional to the current and therefore the
brightness.
For the ISL97634, PWM dimming provides linear dimming
adjustment with low frequency signal, such as 1kHz and
I
LED-AVG
ILED
PWM/EN
V
OUT
FIGURE 8. PWM DIMMING AT 1kHz, D = 99%
=
-------------- - D
R
V
SET
FB
⋅
LX
V
R
L
1
IN
1
March 7, 2008
= 22µH
= 4Ω
= 4V
FN6264.3
(EQ. 2)