MCP3008

The MCP3008 is Microchip's eight-channel, 10-bit successive-approximation analog-to-digital converter with an on-chip sample-and-hold and a four-wire SPI-compatible serial interface. It runs from a single 2.7 V to 5.5 V supply, converts at up to 200 ksps at VDD = 5 V and 75 ksps at 2.7 V, and supports SPI clock modes (0,0) and (1,1) with a maximum serial clock of 3.6 MHz at 5 V and 1.35 MHz at 2.7 V. Linearity is guaranteed at ±1 LSB for both DNL and INL with no missing codes over temperature, which is the figure that separates it from unbranded clones.

The conversion is efficient: the CS/SHDN pin doubles as chip select and shutdown control, a conversion needs ten clock cycles of which the first 1.5 cycles are the acquisition window, and the input configuration word selects either eight single-ended channels or four pseudo-differential pairs. Active supply current is 425 µA typical at VDD = VREF = 5 V and 225 µA typical at 2.7 V, while standby current is 5 nA typical and 2 µA maximum — so a battery node can sleep between scans and still measure hundreds of channels per second when awake.

Two architecture points matter in real designs. First, the reference is external: the VREF pin accepts 0.25 V up to VDD, and it defines full scale. Tie VREF to VDD for maximum range and simplicity, or feed a precision 2.5 V reference for better absolute accuracy and drift performance; note that reference current drain is small (100 µA typical) but the reference must be low impedance. Second, the analog input is a switched-capacitor network with about 20 pF of sampling capacitance behind roughly 1 kΩ of switch resistance, so source impedance should be kept low — under a few kilohms for full 200 ksps operation, or add a buffer op-amp. Microchip also warns that very low clock rates (below about 10 kHz) let the sample capacitor leak and degrade linearity at high temperature, so keep the serial clock reasonable even if you convert slowly.

The MCP3008 is the de facto analog expansion part for single-board computers without an ADC, and Microchip supplies it in 16-pin PDIP and SOIC. Family members let you scale: MCP3004 (four channels, same die family), MCP3208 (12-bit, 100 ksps), MCP3301 (differential 13-bit), and MCP3550/MCP3551 (20-bit delta-sigma for low-speed precision). If you need an internal reference, a PGA or I2C instead of SPI, the ADS1015/ADS1115 is the alternative. Sourcing is easy: the part is high volume, priced in the low single-digit dollar range, and stocked in depth in Shenzhen. MOQ is 1 tube or 1 reel for production, or 50 to 100 pcs loose for prototyping, with 1-2 day local dispatch and 4-12 weeks through the Microchip authorized channel. Counterfeit and remarked material does exist in the hobby channel; verify Microchip laser marking and the full part suffix (MCP3008-I/P for PDIP, MCP3008-I/SL for SOIC), and screen a sample for INL and missing codes with a slow ramp input before qualifying a broker lot.