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User
’s Guide
BD57121MUF-EVK-001
© 2019 ROHM Co., Ltd.
No. 61UG042E Rev.001
JAN.2019
3. Block diagram of the transmitter
BD57121MUF-M operates with a 5.4 V power supply. NFC reader IC ST25R3914 operates with a main power supply of 5.4 V
and a sub of 3.3 V. The STM8AF MCU operates with a main power supply of 3.3 V. The peripheral voltage of the MCU is 3.3 V.
The MCU communicates with the BD57121MUF-M via I
2
C bus, and with the ST25R3914 via SPI bus.
BD57121MUF-M functions as the analog front-end for wireless power transfer that is compliant to Qi ver 1.2.4, and it includes a
D / A converter for voltage control, a pre-driver for driving the inverter bridge, an analog sensing circuit, and a selector circuit for
multiple coils.
ST25R3914 is a high-sensitivity and high-power NFC / HF analog front-end that supports
ISO14443A / B, ISO15693, FeliCa™
and ISO 18092 (NFCIP-1) active P2P. This IC directly drives the NFC antenna. Please contact ST Microelectronics regarding
details of this IC.
CAR Battery
LDO
Buck-Boost
DC/DC
5.4V/1A
Temperature
Sensing Circuits
(option)
Coil Selector
COIL1 COIL2 COIL3
Full Bridge
Qi Resonant Tank
ROHM WPT
BD57121MUF-M
ST Micro MCU
STM8AF
ST Micro
ST25R3914
DAC
V-
monitor
Pre-
drive
I-
monitor
FET
FET
FET
FET
LDO
I
2
C
(3.3V)
SPI
(3.3V)
3.3V/0.15A
12V/3A
Enable SW
Load SW
VDDMCU
VDDA
PI filter
VDDA
VDDMCU
VBUS54
VDDMCU
VBUS54
VDDMCU
VBUS54
NFC Antenna
Figure 3. BD57121MUF-EVK-001 Block diagram
