ISL97635AIRZ-TK Intersil, ISL97635AIRZ-TK Datasheet - Page 26

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

Specifications of ISL97635AIRZ-TK

• 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
• Other names: ISL97635AIRZ-TK

RGB LED Backlight or Scrolling Backlight
Operation
The SMBus control features of PWM dimming, DC dimming,
and random channels selection have offered many driving
possibilities. For example, red, green, and blue LEDs can be
arranged in Ch0 and Ch1, Ch2 and Ch3, Ch4 and Ch5
respectively such that each group can be controlled
independently in sequential order for RGB LED backlighting
applications.
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
FIGURE 32. 16-BIT DIMMING ILLUSTRATION
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Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
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STEP 255 PWM CONTROL
STEP 0~255 DC CONTROL
STEP 254 PWM CONTROL
STEP 1 PWM CONTROL
STEPS 0~255 DC
STEP 0 PWM CONTROL
26
ISL97635A
Compensation
The ISL97635A has two main elements in the system; the
Current Mode Boost Regulator and the op amp based
multi-channel current sources. The ISL97635A incorporates
a transconductance amplifier in its feedback path to allow
the user some levels of adjustment on the transient
response and better regulation. The ISL97635A uses current
mode control architecture, which has a fast current sense
loop and a slow voltage feedback loop. The fast current
feedback loop does not require any compensation. The slow
voltage loop must be compensated for stable operation. The
compensation network is a series Rc, Cc1 network from
COMP pin to ground and an optional Cc2 capacitor
connected to the COMP pin. The Rc sets the high frequency
integrator gain for fast transient response and the Cc1 sets
the integrator zero to ensure loop stability. For most
applications, Rc is in the range of 200Ω to 3kΩ and Cc1 is in
the range of 27nF to 37nF. Depending upon the PCB layout,
a Cc2, in range of 100nF, may be needed to create a pole to
cancel the output capacitor ESR’s zero effect for stability.
The ISL97635A evaluation board is configured with Rc1 of
500Ω, Cc1 of 33nF, and Cc2 of 0, which achieves stability. In
the actual applications, these values may need to be tuned
empirically but the recommended values are usually a good
starting point.
December 22, 2008
FN6564.2