TLC5970
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SBVS140 –MARCH 2010
4. Calculate inductor peak current that should be selected:
The TLC5970 PH peak current must be less than 2 A and ILPK must not be greater than 2 A in any case.
1
Inductor Peak Current (A) = VCC (V, Maximum) ´
Maximum PH Switching Frequency (MHz, Maximum)
Selected PH On-Duty
< 2 A
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.
VCC
Boot Regulator
BOOT
OSC
(10 MHz)
C2
L1
PH
FB
Buck Converter
Switching Control
with Soft-Start
PH High-Side
MOS SW
C1
VREF
UVLO
D1
SCP/TSD
ERR_VO
OR
LEDBn
LEDB1
RRED
DAC
LEDGn
4.0 V
HI_VO
LEDRn
AND
OR
EEPROM
1.1 V
0.9 V
LEDG1
LOW_VO
Buck Converter
Target Voltage
Control
LEDR1
OUT0
LED
5 MHz
OUT1
OUT2
Constant-
Current
Control
1/2
Divider
On-Off
Timing
Control
Clock
Select
External Clock
From Differential
Signal Interface Pin,
SCKA and SCKB
IREF0
IREF1
IREF2
RIREF
RIREF
RIREF
0
1
2
Control Data From
Logic Circuit Block
GND
Figure 21. Buck DC/DC Converter Operation
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