MS51FB9AE-T from Nuvoton Tech, in a TSSOP-20. Pinout and pin descriptions extracted from the manufacturer datasheet by ds2sf; symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin	Name	Type	Function
1	P0.5/AIN4/T0/IC6/PWM2	bidirectional	General purpose I/O P0.5. Alternate functions: ADC channel 4 input (AIN4), Timer 0 external count input (T0), PWM Timer 2 input capture (IC6), PWM channel 2 output (PWM2).
2	P0.6/AIN3/TXD	bidirectional	General purpose I/O P0.6. Alternate functions: ADC channel 3 input (AIN3), UART0 transmit data (TXD).
3	P0.7/AIN2/RXD	bidirectional	General purpose I/O P0.7. Alternate functions: ADC channel 2 input (AIN2), UART0 receive data (RXD).
4	P2.0/RST	input	External active-low reset input (RST) / input-only P2.0. Asserting low resets the MCU.
5	P3.0/AIN1/OSCIN/INT0	bidirectional	General purpose I/O P3.0. Alternate functions: ADC channel 1 input (AIN1), external oscillator/clock input (OSCIN), external interrupt 0 (INT0).
6	P1.7/AIN0/INT1	bidirectional	General purpose I/O P1.7. Alternate functions: ADC channel 0 input (AIN0), external interrupt 1 (INT1).
7	GND	power_in	Ground reference (0 V) for digital and analog supplies.
8	P1.6/OCDDA/ICPDA/TXD_1/[SDA]	bidirectional	General purpose I/O P1.6. Alternate functions: On-Chip Debugger data (OCDDA), In-Circuit Programming data (ICPDA), UART1 TXD, and remappable I2C SDA.
9	VDD	power_in	Positive supply voltage, 2.4 V to 5.5 V.
10	P1.5/SS/IC7/PWM5	bidirectional	General purpose I/O P1.5. Alternate functions: SPI slave select (SS), PWM Timer 2 input capture 7 (IC7), PWM channel 5 output (PWM5).
11	P1.4/PWM1/FB/SDA	bidirectional	General purpose I/O P1.4. Alternate functions: PWM channel 1 output (PWM1), PWM Fault-Brake input (FB), I2C SDA (open-drain).
12	P1.3/SCL/[STADC]	bidirectional	General purpose I/O P1.3. Alternate functions: I2C SCL (open-drain), remappable ADC start-conversion trigger (STADC).
13	P1.2/PWM0/IC0	bidirectional	General purpose I/O P1.2. Alternate functions: PWM channel 0 output (PWM0), PWM Timer 2 input capture 0 (IC0).
14	P1.1/PWM1/IC1/AIN7/CLO	bidirectional	General purpose I/O P1.1. Alternate functions: PWM channel 1 output (PWM1), input capture 1 (IC1), ADC channel 7 input (AIN7), clock output (CLO).
15	P1.0/PWM2/IC2/SPCLK	bidirectional	General purpose I/O P1.0. Alternate functions: PWM channel 2 output (PWM2), input capture 2 (IC2), SPI clock (SPCLK).
16	P0.0/PWM3/IC3/MOSI/T1	bidirectional	General purpose I/O P0.0. Alternate functions: PWM channel 3 output (PWM3), input capture 3 (IC3), SPI master-out slave-in (MOSI), Timer 1 external count input (T1).
17	P0.1/PWM4/IC4/MISO	bidirectional	General purpose I/O P0.1. Alternate functions: PWM channel 4 output (PWM4), input capture 4 (IC4), SPI master-in slave-out (MISO).
18	P0.2/ICPCK/OCDCK/RXD_1/[SCL]	bidirectional	General purpose I/O P0.2. Alternate functions: In-Circuit Programming clock (ICPCK), On-Chip Debugger clock (OCDCK), UART1 receive data (RXD_1), remappable I2C SCL.
19	P0.3/PWM5/IC5/AIN6	bidirectional	General purpose I/O P0.3. Alternate functions: PWM channel 5 output (PWM5), input capture 5 (IC5), ADC channel 6 input (AIN6).
20	P0.4/AIN5/STADC/PWM3/IC3	bidirectional	General purpose I/O P0.4. Alternate functions: ADC channel 5 input (AIN5), ADC start-conversion trigger (STADC), PWM channel 3 output (PWM3), input capture 3 (IC3).

Key specifications

Parameter	Value
Manufacturer	Nuvoton Tech
Package	TSSOP-20
Category	MCU
Pins	20

Ordering variants

Same part, different packaging or reel option.

MS51FB9AE-T
MS51XB9AE
MS51XB9BE
MS51BA9AE
MS51DA9AE

CAD (KiCad official)

Symbol: MS51FB9AE-T
Footprint: Package_SO:TSSOP-20_4.4x6.5mm_P0.65mm
3D model: TSSOP-20 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`ms51fb9ae-t.step`	267 KB	You want the bare part, or you mark your own boards.
`ms51fb9ae-t-etched.step`	2.6 MB	You want the part with `MS51FB9AE-T` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 662 faces against 327 in the bare model. It survives export, section views, and rendering in any CAD tool, and it drops straight into KiCad or Fusion with no extra setup.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Nuvoton Tech datasheet (25 pp, sha256 471cbcb0dd4795df, retrieved 2026-08-17, tier: lcsc)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF