TLC5970
SBVS140 –MARCH 2010
www.ti.com
LED Is Off
LED Is On
LED Is Off
FB target voltage set by the DAC.
FB
Voltage
5. The FB voltage increases because the
current is charged from L1 into C1.
The FB voltage falling slope
becomes mild when the LED
lamp is turned off.
The FB voltage falling slope becomes sharp
when the LED lamp is turned on.
1. When the FB voltage falls below the FB target voltage
set by the DAC, the MOS switcher is turned on to
synchronize the internal oscillator with the EEPROM-programmed on-time.
ON
MOS
Switcher
OFF
2. The PH voltage goes to a VCC level when the MOS swicher
is turned on and then charges the current to L1.
6. When the L1 current becomes zero, the resonance starts.
VCC
FB
PH
GND
D1 Forward Voltage
4. PH voltage drops with the D1 forward voltage from GND.
3. When the MOS switcher is turned off, the current
in the inductor is discharged to the capacitor connected to FB.
L1
Current
0 mA
Figure 22. Buck DC/DC Converter Block Diagram
28
Submit Documentation Feedback
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): TLC5970
TI [ TEXAS INSTRUMENTS ]
