CAT4237TD-GT3 ON Semiconductor, CAT4237TD-GT3 Datasheet - Page 10

• Manufacturer Part Number: CAT4237TD-GT3
• Description: IC LED DRVR WHT BCKLGHT TSOT23-5
• Manufacturer: ON Semiconductor
• Type: Backlight, White LEDr

Specifications of CAT4237TD-GT3

• Constant Current: Yes
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 800kHz ~ 1.3MHz
• Voltage - Supply: 2.8 V ~ 5.5 V
• Voltage - Output: 30V
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-5, TSOT-5, TSOP-5
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 40mA
• Internal Switch(s): Yes
• Efficiency: 87%
• Number Of Digits: 8
• Low Level Output Current: 1 mA
• High Level Output Current: 40 mA
• Operating Supply Voltage: 2.8 V to 5.5 V
• Maximum Supply Current: 1.5 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: CAT4237TD-GT3TR

Dimming Control
brightness.
PWM Signal on the SHDN Pin
signal to the SHDN input. The LED current is repetitively
turned on and off, so that the average current is proportional
to the duty cycle. A 100% duty cycle, with SHDN always
high, corresponds to the LEDs at nominal current. Figure 25
shows a 1 kHz signal with a 50% duty cycle applied to the
SHDN pin. The recommended PWM frequency range is
from 100 Hz to 2 kHz.
Filtered PWM Signal
control the LED current. Figure 26 shows the PWM control
circuitry connected to the CAT4237 FB pin. The PWM
signal has a voltage swing of 0 V to 2.5 V. The LED current
can be dimmed within a range from 0 mA to 20 mA. The
PWM signal frequency can vary from very low frequency up
to 100 kHz.
Figure 25. Switching Waveform with 1 kHz PWM on
There are several methods available to control the LED
LED brightness dimming can be done by applying a PWM
A filtered PWM signal used as a variable DC voltage can
SHDN
http://onsemi.com
10
a max LED current of about 22 mA. A PWM signal with a
93% duty cycle or more, results in an LED current of 0 mA.
2.5 V
0 V
A PWM signal at 0 V DC, or a 0% duty cycle, results in
25
20
15
10
5
0
Figure 27. Filtered PWM Dimming (0 V to 2.5 V)
Signal
PWN
0
Figure 26. Circuit for Filtered PWM Signal
10
VIN
20
3.73 kW
0.22 mF
PWM DUTY CYCLE (%)
R
A
30
C1
VIN
SHDN
GND
40
3.1 kW
CAT4237
R
B
50
FB
V
i
SW
FB
60
= 300 mV
1 kW
R
2
70
80
R
15 W
1
90 100
LED
Current