AFE4403_15 Datasheet, PDF (74/97 Pages) Texas Instruments – AFE4403 Ultra-Small, Integrated Analog Front-End for Heart Rate Monitors and Low-Cost Pulse Oximeters

AFE4403
SBAS650B – MAY 2014 – REVISED JULY 2014
www.ti.com
Figure 108. LEDCNTRL: LED Control Register (Address = 22h, Reset Value = 0000h)
23
22
21
20
19
18
17
16
15
14
13
12
0
0
0
0
0
0
LED_RANGE[1:0]
LED1[7:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED1[7:0]
LED2[7:0]
This register sets the LED current range and the LED1 and LED2 drive current.
Bits 23:18
Bits 17:16
Bits 15:8
Bits 7:0
Must be 0
LED_RANGE[1:0]: LED range
These bits program the full-scale LED current range for Tx. Table 7 details the settings.
LED1[7:0]: Program LED current for LED1 signal
Use these register bits to specify the LED current setting for LED1 (default after reset is
00h).
The nominal value of the LED current is given by Equation 7, where the full-scale LED
current is either 0 mA or 50 mA (as specified by the LED_RANGE[1:0] register bits).
LED2[7:0]: Program LED current for LED2 signal
Use these register bits to specify the LED current setting for LED2 (default after reset is
00h).
The nominal value of LED current is given by Equation 8, where the full-scale LED current is
either 0 mA or 50 mA (as specified by the LED_RANGE[1:0] register bits).
Table 7. Full-Scale LED Current across Tx Reference Voltage Settings⁽¹⁾
LED_RANGE[1:
0]
00 (default after
reset)
01
10
11
TX_REF = 0.25 V
I_MAX
V_HR ⁽²⁾
50 mA
0.75 V
25 mA
50 mA
Tx is off
0.7 V
0.75 V
—
TX_REF = 0.5 V
I_MAX
V_HR
100 mA
1.1 V
50 mA
100 mA
Tx is off
1.0 V
1.1 V
—
TX_REF = 0.75 V
I_MAX
V_HR
Do not use
—
75 mA
Do not use
Tx is off
1.3 V
—
—
TX_REF = 1.0 V
I_MAX
V_HR
Do not use
—
100 mA
Do not use
Tx is off
1.6 V
—
—
(1) For a 3-V to 3.6-V supply, use TX_REF = 0.25 or 0.5 V. For a 4.75-V to 5.25-V supply, use TX_REF = 0.75 V or 1.0 V.
(2) V_HR refers to the headroom voltage (over and above the LED forward voltage and cable voltage drop) needed on the LED_DRV_SUP.
The V_HR values specified are for the H-bridge configuration. In the common anode configuration, V_HR can be lower by 0.25 V.
LED1[7:0]
256 ^{´ Full-Scale Current}
(7)
LED2[7:0]
256 ^{´ Full-Scale Current}
(8)
74
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