Product Info

1.2 Programming and Debug Interface
LM746 provides a debug SPI interface for programming, configuring (PS Keys) and debugging the LM746. Access to this interface is required in
production. Ensure the 4 SPI signals and the SPI line are brought out to either test points or a header. To use the SPI interface, the SPI line requires the
option of being pulled high externally.
2.1 Analogue I/O Ports, AIO
LM746 has 2 general-purpose analogue interface pin, AIO[0] & AIO[1]. Typically, this connects to a thermistor for battery pack temperature measure-
ments during charge control.
2.2 LED Drivers
LM746 includes a 3-pad synchronised PWM LED driver for driving RGB LEDs for producing a wide range of colours. All LEDs are controlled by
firmware.
The terminals are open-drain outputs, so the LED must be connected from a positive supply rail to the pad in series with a current-limiting resistor.
Figure 2.1: LED Equivalent Circuit
From Figure 2.1 it is possible to derive Equation 2.1 to calculate ILED. If a known value of current is required through the LED to give a specific luminous
intensity, then the value of RLED is calculated.
Equation 2.1: LED Current
For the LED pads to act as resistance, the external series resistor, RLED, needs to be such that the voltage drop across it, VR, keeps VPAD below 0.5V.
Equation 2.2 also applies.
VDD = VF + VR + VPAD
Equation 2.2: LED PAD Voltage
Note: The LED current adds to the overall current. Conservative LED selection extends battery life.
LM746 Bluetooth® Dual Mode Audio Module
Standalone (With Embedded Bluetooth® 5 Compliant Stack)
1. Serial Interface
2. Interfaces
LED Forward Voltage, V
F
Resistor Voltage Drop, V
LED[2, 1 or 0]
R
Pad Voltage V
PAD
R =20Ω
ON
R
LED
LED
I
VDD - V
F
R
LED
LED
R
ON
I
=
+
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