4.4 LDOs
The device is equipped with 2 internal low dropout regulators (LDOs) – a 5 V and a 1.8 V one, with the latter
deriving its power from the former.
The 1.8 V LDO powers the digital part of the IC, while the 5 V LDO powers the analog part of the IC but can also
be used to power external low-power circuitry (such as LEDs). The maximum current externally drawn from this
LDO should not exceed 10 mA.
External LDO capacitors should be placed as close to the IC as possible.
4.5
Power-up sequence
Once power is applied to the input (and the device is not forced into reset), the power-up sequence of the device
starts. After the internal main LDO reaches the target output voltage, the digital core of the device starts
operating. Default device settings are used until the digital core is woken up after which the firmware loads
settings saved in the Configuration file.
If both Patch and Configuration files are loaded into the device and the automatic start function is enabled, the
device enters the digital ping phase of power transfer (see Section 4.11 WPC Qi wireless power transfer). If the
automatic start function is disabled, the device does not proceed to the ping phase until the TX_EN command is
executed.
If Patch and/or Configuration files are not loaded, the device stays in a so-called DC mode. In this mode, the
device is powered up and ready to be programmed. The device also enters this mode if either the Patch or
Configuration, or both files, are corrupt.
4.6 UVLO
The STWBC86 is also equipped with a UVLO function. The UVLO is triggered when the input voltage drops below
2.9 V. The inverter stops switching and the device is powered down. Normal operation is resumed as soon as the
input voltage rises above 3 V.
4.7
Chip reset
The device can be forced into reset by pulling the RSTB pin to ground. This can easily be done by a jumper on
header P14. When the RSTB pin is released and allowed to be pulled up, the device resumes normal operation.
4.8
Protections overview
The STEVAL-WBC86TX board uses both hardware and software protection to ensure safe voltage and current
levels. The purpose of those protections is to avoid damage to either the board itself or even the potential
receiver, caused by unexpected conditions – overvoltage and/or overcurrent. The temperature is also monitored,
although only software protection is used for this purpose.
The software protections can be enabled/disabled in the GUI; the GUI can also be used to adjust thresholds for
the respective protections.
The hardware protections are permanently set and cannot be disabled or adjusted in the GUI. The thresholds for
the hardware protections are as follows:
• Overcurrent protection: 3 A (fuse)
• Overvoltage protection: 22 V (TVS diode)
The triggering of a software protection results in the transmitter terminating a power transfer and generating a
corresponding interrupt (can be configured in the GUI).
4.8.1 Overcurrent protection (OCP)
A transmitter overload or a short on the output (transmitting coil) may lead to excessive input current values. To
prevent damage to the transmitter caused by such currents, two separate protections (hardware and software)
are implemented.
A fuse (F1) on the input track rated at 3 A serves as the hardware protection, while an ADC monitoring the input
current serves as the software one. If the input current exceeds a set threshold, the power transmitter terminates
the power transfer and generates an OCP interrupt. The threshold is configurable in the GUI and can be set in a
range of 0 to 2500 mA.
UM3161
LDOs
UM3161 - Rev 1
page 17/78
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