TLC5970 Datasheet, PDF (27/48 Pages) Texas Instruments – 3-Channel, 12-Bit, PWM LED Driver with Buck DC/DC Converter and Differential Signal Interface

TLC5970
www.ti.com
SBVS140 – MARCH 2010
4. Calculate inductor peak current that should be selected:
The TLC5970 PH peak current must be less than 2 A and I_LPK must not be greater than 2 A in any case.
Inductor Peak Current (A) = VCC (V, Maximum) ´
1
Maximum PH Switching Frequency (MHz, Maximum)
Selected PH On-Duty
<2A
Inductor Value (mH)
(11)
Example: In this case, 25 × 0.67 × 0.29/4.2 = 1.15 A. So the inductor value is correct.
As the result of the above calculation, the inductor value should be selected over 4.2 µH and the inductor
peak current should be over 1.15 A.
Figure 21 shows a block diagram of the buck dc/dc converter; Figure 22 details the buck dc/dc converter
operation. Figure 23 and Figure 24 illustrate the timings of the external and internal GS clock mode for PWM
operation, respectively.
OSC
(10 MHz)
VREF
UVLO
DAC
EEPROM
Buck Converter
Target Voltage
Control
Boot Regulator
VCC
BOOT
C2
Buck Converter
PH
L1
Switching Control
with Soft-Start
PH High-Side
MOS SW
D1
C1
SCP/TSD
FB
ERR_VO
OR
HI_VO
AND
LOW_VO
OR
4.0 V
1.1 V
R_RED
LEDRn
LEDR1
LEDGn
LEDG1
LEDBn
LEDB1
1/2
Divider
External Clock
From Differential
Signal Interface Pin,
SCKA and SCKB
5 MHz
Clock
Select
LED
On-Off
Timing
Control
Control Data From
Logic Circuit Block
GND
Constant-
Current
Control
0.9 V
OUT0
OUT1
OUT2
IREF0
IREF1
IREF2
R_IREF0
R_IREF1
R_IREF2
Figure 21. Buck DC/DC Converter Operation
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