PCA9508DP: Hot swappable level translating I2C-bus repeater

The PCA9508 is a CMOS integrated circuit that supports hot-swap with zero offset and provides level shifting between low voltage (down to 0.9 V) and higher voltage (2.7 V to 5.5 V) for I²C-bus or SMBus applications. While retaining all the operating modes and features of the I²C-bus system during the level shifts, it also permits extension of the I²C-bus by providing bidirectional buffering for both the data (SDA) and the clock (SCL) lines, thus enabling two buses of 400 pF. Using the PCA9508 enables the system designer to isolate two halves of a bus for both voltage and capacitance, and perform hot-swap and voltage level translation. Furthermore, the dual supply pins can be powered up in any sequence; when any of the supply pins are unpowered, the 5 V tolerant I/O are high-impedance.

The hot swap feature allows an I/O card to be inserted into a live backplane without corrupting the data and clock buses. Control circuitry prevents the backplane from being connected to the card until a stop command or bus idle occurs on the backplane without bus contention on the card. Zero offset output voltage allows multiple PCA9508s to be put in series and still maintains an excellent noise margin.

PCA9508 has B side and A side bus drivers. The 2.7 V to 5.5 V bus B side drivers behave much like the drivers on the PCA9515A device, while the adjustable voltage bus A side drivers drive more current and incur no static offset voltage. This results in a LOW on the B side translating into a nearly 0 V LOW on the A side.

The static offset design of the B side PCA9508 I/O drivers prevents them from being connected to another device that has a rise time accelerator including the PCA9510/A, PCA9511/A, PCA9512/A, PCA9513/A, or PCA9514/A or a static offset voltage including the PCA9507 (B side), PCA9508 (B side), PCA9509 (A side), PCA9515/A, PCA9516A, PCA9517/A (B side), PCA9518, PCA9519 (A side), or P82B96/PCA9600 (Sx/Sy side). The A side of two or more PCA9508s can be connected together, however, to allow a star topology with the A side on the common bus, and the A side can be connected directly to any other buffer with static or dynamic offset voltage. Multiple PCA9508s can be connected in series, A side to B side, with no build-up in offset voltage with only time-of-flight delays to consider.

The PCA9508 drivers are not enabled unless the bus is idle, VCC(A) is above 0.8 V and VCC(B) is above 2.5 V. The EN pin can also be used to turn the drivers on and off under system control. Caution should be observed to only change the state of the enable pin when the bus is idle.

The output pull-down on the B side internal buffer LOW is set for approximately 0.5 V, while the input threshold of the internal buffer is set about 70 mV lower (0.43 V). When the B side I/O is driven LOW internally, the LOW is not recognized as a LOW by the input. This prevents a lock-up condition from occurring. The output pull-down on the A side drives a hard LOW and the input level is set at 0.5VCC(A) to accommodate the need for a lower LOW level in systems where the low voltage side supply voltage is as low as 0.9 V.

Outline 3d SOT505-1
Data Sheets (1)
Name/DescriptionModified Date
Hot swappable level translating I2C-bus repeater (REV 1.0) PDF (128.0 kB) PCA950828 Apr 2008
Application Notes (3)
Name/DescriptionModified Date
PCA9500/PCA9501 provides simple card maintenance and control using I²C-bus (REV 1.0) PDF (90.0 kB) AN25623 Mar 2009
Level shifting techniques in I2C-bus design (REV 1.0) PDF (52.0 kB) AN1044120 Jun 2007
I2C / SMBus Repeaters, Hubs and Expanders (REV 2.0) PDF (1.0 MB) AN25519 Dec 2002
Users Guides (4)
Name/DescriptionModified Date
I2C-bus specification and user manual (REV 6.0) PDF (1.4 MB) UM1020428 Apr 2014
I2C-bus specification and user manual (REV 5.0) PDF (1.6 MB) UM10204_JA03 Apr 2013
PCA9600 demonstration board OM6293 (REV 1.0) PDF (130.0 kB) UM1032315 Dec 2008
I2C Demonstration Board 2005-1 Quick Start Guide (REV 1.0) PDF (261.0 kB) UM1020613 Jun 2006
Brochures (2)
Name/DescriptionModified Date
NXP® I2C-bus solutions 2014: Smart, simple solutions for the 12 most common design concerns (REV 1.0) PDF (3.5 MB) 7501754001 Aug 2014
Extend the I2C-bus with advanced repeaters and hubs; NXP® 2-channel I2C-bus repeaters PCA9515x and... (REV 1.0) PDF (740.0 kB) 7501653201 Jul 2008
Package Information (1)
Name/DescriptionModified Date
plastic thin shrink small outline package; 8 leads; body width 3 mm (REV 1.0) PDF (240.0 kB) SOT505-108 Feb 2016
Packing (1)
Name/DescriptionModified Date
TSSOP8; Reel pack; SMD, 13" Q1/T1 Standard product orientation Orderable part number ending ,118 or... (REV 1.0) PDF (214.0 kB) SOT505-1_11815 Apr 2013
Supporting Information (1)
Name/DescriptionModified Date
Reflow Soldering Profile (REV 1.0) PDF (34.0 kB) REFLOW_SOLDERING_PROFILE30 Sep 2013
Ordering Information
ProductStatusPackage versionApplicationEnableFunctionOperating Temperature (Cel)Number of bitsVoltage Translation Range (V)Operating voltage (VDC)Operating voltage 2 (V)InputsOutputsTTL Drive (mA)GTL Drive (mA)I2C-bus (kHz)
PCA9508DPActiveSOT505-1-40~852.7~5.50.9~5.511400
Package Information
Product IDPackage DescriptionOutline VersionReflow/Wave SolderingPackingProduct StatusPart NumberOrdering code(12NC)MarkingChemical ContentRoHS / Pb Free / RHFLeadFree Conversion DateEFRIFR(FIT)MTBF(hour)MSLMSL LF
PCA9508DPSOT505-1Reflow_Soldering_ProfileReel 13" Q1/T1ActivePCA9508DP,118 (9352 856 73118)9508PCA9508DPAlways Pb-free0.02.05E811
Hot swappable level translating I2C-bus repeater pca9508dp
PCA9500/PCA9501 provides simple card maintenance and control using I²C-bus PCA9553
Level shifting techniques in I2C-bus design pca9685pw
I2C / SMBus Repeaters, Hubs and Expanders pca9600
I2C-bus specification and user manual pca9685pw
I2C-bus specification and user manual pca9685pw
PCA9600 demonstration board OM6293 pca9600
I2C Demonstration Board 2005-1 Quick Start Guide pca9685pw
NXP® I2C-bus solutions 2014: Smart, simple solutions for the 12 most common design concerns pca9685pw
Extend the I2C-bus with advanced repeaters and hubs; NXP® 2-channel I2C-bus repeaters PCA9515x and... pca9600
plastic thin shrink small outline package; 8 leads; body width 3 mm pesd5v0l7bas
Reflow_Soldering_Profile Wave_Soldering_Profile LPC1112FD20
TSSOP8; Reel pack; SMD, 13" Q1/T1 Standard product orientation Orderable part number ending ,118 or... pesd5v0l7bas
PCT2075