VSP5620 Datasheet, PDF (32/41 Pages) Texas Instruments – 16-Bit, 4-Channel, CCD/CMOS Sensor Analog Front-End with LED Driver

VSP5620
VSP5621
VSP5622
SBES022 – JULY 2011
LED DRIVER
www.ti.com
These devices have three constant-current sink LED driver channels. The output current for each channel can be
independently set via register settings within a 0 mA to 60 mA range in 4-mA steps. The maximum allowable
total constant-current value for all three channel drivers is 120 mA. Because the circuitry that limits the total
constant-current is not incorporated, the current value should be carefully set when multiple channels are
concurrently active.
Figure 20 shows an LED driver block diagram and the connection with the external LED device. This driver
supports V_LD (driver voltage) within a range of 0.7 V to 4.5 V. V_LD depends on the V_F (LED forward voltage)
because this driver is a constant-current source. The LED driver power consumption, defined as V_LD × I_LD (LED
current), affects package temperature. Therefore, when V_F is small, it is recommended to insert an external
resister between LEDn (the LED driver pin) and LEDVDD (the LED power supply) to reduce thermal affects
caused by high-power consumption.
LEDn_EN
(Register)
EN_LED
Fine Current Cell
1 mA x 4
Coarse Current Cell
4 mA x 14
LEDn_EN
LEDVDD
Vf
R
LEDn
R x ILD
・・・・
VLD
1mA 1mA 1mA 1mA
4mA
4mA 4mA
ILD
LEDVSS
Figure 20. LED Driver Block Diagram
This driver can be turned on or off with a combination of logic circuitry driven by internal register settings and
external pins, as shown in Table 13. Note that the internal EN_LED register should be set to '1' to enable the
logic circuit.
EN_LED REGISTER
0
1
(1) n = 1, 2, and 3.
Table 13. LED Driver Control Register and Pin Setting⁽¹⁾
LEDN_EN PIN SETTING
X
Low
Low
High
High
LEDN_EN REGISTER
X
0
1
0
1
LED DRIVER STATE
Disabled
Disabled
Enabled
Enabled
Disabled
32
Submit Documentation Feedback
Copyright © 2011, Texas Instruments Incorporated
Product Folder Link(s): VSP5620 VSP5621 VSP5622