Datasheet

50
55
60
65
70
75
80
85
90
95
100
2 2.5 3 3.5 4 4.5 5 5.5
V -InputVoltage
I
Efficiency-%
V.mmARIV
LEDsense
17805103503 =W´=´=
V.V.V.VVV
senseFBR
32201780500
1
=-=-=
V.V.V.VVV
FBREFR
00250052
2
=-=-=
W=== k.
mA.
V.
mA.
V
R
R
223
10
3220
10
1
1
W=== k
mA.
V.
mA.
V
R
R
20
10
002
10
2
2
www.ti.com Test Results
3 Test Results
Figure 1. Efficiency vs Input Voltage
4 Design Procedure for Divider Network
The TPS63030 feedback voltage (FB) is set to 0.50 V. If this were used for current regulation, the power
dissipation of the sense resistor will be high. To reduce power dissipation on the current sense resistor
R3, a reference voltage of 2.5 V is summed with it, thereby reducing V
sense
voltage and power dissipation
in R3.
The first step is to choose the LED operating current and V
sense
voltage, which determines the value for
R3. There is a trade off between power dissipation on R3 and accuracy of regulation point. As V
sense
is
increased, the current regulation accuracy improves; the maximum voltage is 0.50 V. As V
sense
is
decreased, the power dissipation is reduced, but the error due to V
ref
on resistors R1 and R2 increases.
The EVM I
LED
is set to 350 mA with a V
sense
voltage of 0.178 V.
Choose divider current of 0.1 mA.
Standard value is 3.24 kΩ.
Standard value is 20 kΩ.
Output current can be increased or decreased by changing R3. For 700-mA output current, decrease R3
to 250 mΩ. Changes in the reference voltage, R1 or R2, also can be used to change the LED current.
3
SLVU391–August 2010 TPS63030EVM-658
Copyright © 2010, Texas Instruments Incorporated