C8051F340-GQR: Mixed‑Signal 8‑Bit MCU with Full‑Speed USB – Complete Overview

The C8051F340-GQR from Silicon Labs is a highly integrated mixed‑signal system‑on‑chip (SoC) microcontroller from the C8051F34x family. Built around an enhanced 8051 core running at up to 48 MHz, it features 64 KB of Flash program memory and 4.25 KB of RAM. Its standout feature is the integrated full‑speed USB 2.0 function controller, eliminating the need for an external USB chip. On‑chip peripherals include a 10‑bit ADC, voltage comparators, and a temperature sensor. Housed in a 48‑pin TQFP package (7×7 mm) , it operates from 2.7 V to 3.6 V over the industrial temperature range of ‑40°C to +85°C.

Key Parameters at a Glance

Parameter	Value	Remarks
CPU Core	8051 (enhanced pipelined architecture)	70% of instructions execute in 1‑2 clock cycles
Max Clock Frequency	48 MHz	Delivers up to 48 MIPS
Program Memory	64 KB Flash	512‑byte sectors, in‑system programmable
RAM	4.25 KB	4352 bytes
USB Controller	USB 2.0 full‑speed (12 Mbps) / low‑speed (1.5 Mbps)	Integrated transceiver + 1‑KB buffer, 8 endpoints
ADC	10‑bit, 200 ksps, 20 channels	Single‑ended/differential inputs, on‑chip temperature sensor
Digital I/O	40 pins	All 5‑V tolerant
Serial Interfaces	UART×2, SPI, SMBus/I²C	Enhanced hardware
Timers	4×16‑bit timers + 5‑channel PCA	Supports PWM output
Operating Voltage	2.7 V ~ 3.6 V	On‑chip regulator supports 3.6 V ~ 5.25 V input
Temperature Range	‑40°C ~ +85°C	Industrial grade
Package	TQFP‑48 (7×7 mm)	Surface‑mount
Debug Interface	On‑chip C2 debug interface	Non‑intrusive, no emulator required
Lifecycle Status	Not Recommended for New Designs (NRND)	Marked on the official website

Typical Applications

Thanks to its combination of full‑speed USB 2.0, a high‑speed 8051 core, and a 10‑bit ADC, the C8051F340-GQR is widely used in:

USB Peripherals and PC Accessories – USB‑to‑serial adapters, game controllers, USB modems.

Industrial Control and Data Acquisition – The on‑chip high‑speed ADC plus USB bus enables low‑cost data‑logging systems.

Portable Medical Devices – Consumer medical instruments.

POS Terminals and Communication Equipment – Point‑of‑sale terminals, IP phones.

Legacy Interface Upgrades – Converting RS‑232 serial devices to USB.

Design Note: Silicon Labs has marked the C8051F340-GQR as "Not Recommended for New Designs (NRND)" . For brand‑new projects, consider evaluating newer USB MCUs from Silicon Labs. However, for maintaining existing products or cost‑sensitive volume production, this chip still offers good availability.

Frequently Asked Questions (Q&A)
Q1: Does the C8051F340-GQR require an external crystal for USB operation?

A: No. The chip integrates a clock recovery circuit and, together with the internal calibrated oscillator and a 4× clock multiplier, provides a stable clock source for both full‑speed (12 Mbps) and low‑speed (1.5 Mbps) USB modes. An external crystal can also be used if desired.

Q2: What are the key features of the ADC?

A: The on‑chip ADC is a true 10‑bit converter with a 200‑ksps sampling rate, supporting 20 external input channels in single‑ended or differential mode. It also includes an internal temperature sensor (±3°C accuracy) and a 2.4‑V internal voltage reference.

Q3: How many I/O pins are available in the TQFP‑48 package?

A: 40 digital I/O pins. All I/O are 5‑V tolerant, allowing direct connection to 5‑V logic peripherals without level shifters.

Q4: What is the difference between the C8051F340-GQR and the C8051F340-GQ?

A: The electrical parameters are identical. The difference is in packaging: the "GQR" suffix denotes tape‑and‑reel packaging for automated SMT assembly, while "GQ" comes in tray format.

In summary, the C8051F340-GQR is a highly integrated mixed‑signal MCU that combines full‑speed USB 2.0, a high‑performance 8051 core, and a 10‑bit ADC. Although it has entered the later stage of its product lifecycle, it remains a valuable option for industrial control, USB peripherals, data acquisition, and other legacy applications.

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