CAT32TDI-GT3 ON Semiconductor, CAT32TDI-GT3 Datasheet - Page 8

• Manufacturer Part Number: CAT32TDI-GT3
• Description: IC WHITE LED DRIVER TSOT-23-6
• Manufacturer: ON Semiconductor
• Type: Backlight, White LEDr

Specifications of CAT32TDI-GT3

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 800kHz ~ 1.6MHz
• Voltage - Supply: 2 V ~ 7 V
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-6, TSOT-6
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 40mA
• Internal Switch(s): Yes
• Efficiency: 83%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Details

to choose R
15 mA to 20 mA. Some higher power designs will use two
parallel strings of LEDs for greater light output, resulting in
30 mA to 40 mA (two strings of 15 mA to 20 mA) flowing
into the LED pin.
LED Dimming with PWM Signal
range (greater than 20:1). By turning the LEDs ON and OFF
using the control signal the LEDs operate at either zero or
full current, but their average current changes with the PWM
signal duty cycle. Typically, a 5 kHz to 40 kHz PWM signal
is used. PWM dimming with the CAT32 can be
accomplished two different ways.
added to drive the RSET pin. If the SHDN pin is used,
increasing the duty cycle will increase the LED brightness.
Using this method, the LEDs can be dimmed and turned off
completely using the same control signal. A 0% duty cycle
signal will turn off the CAT32, reducing the total quiescent
current to near zero.
decrease the brightness. Using this method, the LEDs are
dimmed using RSET and turned off completely using
SHDN. If the RSET pin is used to provide PWM dimming,
the approximate value of R
V
Table 8. R
MAX
CAT32
SHDN
For other LED current values, use the following equation
Most white LEDs are driven at maximum currents of
PWM brightness control provides the widest dimming
The SHDN pin can be driven directly or a resistor can be
If the RSET pin is used, increasing the duty cycle will
5
is the “HIGH” value of the PWM signal):
I
PWM
LED
SET
SET
R
40
30
25
20
15
10
5
(mA)
PWM
.
R
RESISTOR VALUES
SET
R
CAT32
RSET
+ R
SET
4
SET
+ 255
R
PWM
PWM
should be calculated (where
0.15 V
PWM
V
0.1 V
MAX
I
LED
* 1
R
1.13 kW
1.50 kW
2.26 kW
4.53 kW
562 W
750 W
909 W
R
SET
SET
Figure 15. LED Dimming Circuits
CAT32
RSET
4
10 kW
http://onsemi.com
R
PWM
0.1 mF
8
brightness control also ensures the “purest” white LED color
over the entire dimming range. The true color of a white
LED changes with operating current, and is the “purest”
white at a specific forward current, usually 15 mA or
20 mA. If the LED current is less than or more than this
value, the emitted light becomes more blue. Applications
involving color LCDs can find the blue tint objectionable.
of the CAT32, the LEDs are turned off and on at the PWM
frequency. The current through them alternates between full
current and zero current, so the average current changes with
duty cycle. This ensures that when the LEDs are on, they can
be driven at the appropriate current to give the purest white
light. LED brightness varies linearly with the PWM duty
cycle.
LED Dimming with a Logic Signal
discrete steps, a logic signal can be used. RMIN sets the
minimum LED current value (when the NMOS is OFF):
R
the external NMOS switch is turned ON.
LED Dimming with a DC Voltage
PCB Layout Guidelines
therefore proper PCB board layout and component
placement can minimize noise and radiation and increase
efficiency. To maximize efficiency, the CAT32 design has
fast switch rise and fall times. To prevent radiation and high
frequency resonance problems minimize the length and area
of all traces connected to the SW pin and use a ground plane
under the switching regulator.
signal path should be kept as short as possible. The ground
connection for the R
GND pin and not be shared with other components.
INCR
PWM
In addition to providing the widest dimming range, PWM
When a PWM control signal is used to drive the SHDN pin
For applications that need to adjust the LED brightness in
The CAT32 is a high−frequency switching regulator and
The switch, schottky output diode and output capacitor
determines how much LED current increases when
R
SET
R
CAT32
RSET
ADJ
4
R
+ 225
INCR
R
R
ADJ
MIN
SET
+ 255
+ 255
resistor should be tied directly to the
V
DC
I
LED(MAX)
R
MIN
V
CAT32
I
MAX
RSET
LED(Increase)
I
LED(MIN)
0.1 V
0.1 V
4
* I
* 0.1 V
R
INCR
LEAD(MIN)
Logic
Signal