PCA9541A: 2-to-1 I²C-bus master selector with interrupt logic and reset

The PCA9541A is a 2-to-1 I²C-bus master selector designed for high reliability dual master I²C-bus applications where system operation is required, even when one master fails or the controller card is removed for maintenance. The two masters (for example, primary and back-up) are located on separate I²C-buses that connect to the same downstream I²C-bus slave devices. I²C-bus commands are sent by either I²C-bus master and are used to select one master at a time. Either master at any time can gain control of the slave devices if the other master is disabled or removed from the system. The failed master is isolated from the system and will not affect communication between the on-line master and the slave devices on the downstream I²C-bus.

Two versions are offered for different architectures. PCA9541A/01 with channel 0 selected at start-up, and PCA9541A/03 with no channel selected after start-up.

The interrupt outputs are used to provide an indication of which master has control of the bus. One interrupt input (INT_IN) collects downstream information and propagates it to the 2 upstream I²C-buses (INT0 and INT1) if enabled. INT0 and INT1 are also used to let the previous bus master know that it is not in control of the bus anymore and to indicate the completion of the bus recovery/initialization sequence. Those interrupts can be disabled and will not generate an interrupt if the masking option is set.

A bus recovery/initialization if enabled sends nine clock pulses, a not acknowledge, and a STOP condition in order to set the downstream I²C-bus devices to an initialized state before actually switching the channel to the selected master.

An interrupt is sent to the upstream channel when the recovery/initialization procedure is completed.

An internal bus sensor senses the downstream I²C-bus traffic and generates an interrupt if a channel switch occurs during a non-idle bus condition. This function is enabled when the PCA9541A recovery/initialization is not used. The interrupt signal informs the master that an external I²C-bus recovery/initialization must be performed. It can be disabled and an interrupt will not be generated.

The pass gates of the switches are constructed such that the VDD pin can be used to limit the maximum high voltage, which will be passed by the PCA9541A. This allows the use of different bus voltages on each pair, so that 1.8 V, 2.5 V, or 3.3 V devices can communicate with 5 V devices without any additional protection.

The PCA9541A does not isolate the capacitive loading on either side of the device, so the designer must take into account all trace and device capacitances on both sides of the device, and pull-up resistors must be used on all channels.

External pull-up resistors pull the bus to the desired voltage level for each channel. All I/O pins are 6.0 V tolerant.

An active LOW reset input allows the PCA9541A to be initialized. Pulling the RESET pin LOW resets the I²C-bus state machine and configures the device to its default state as does the internal Power-On Reset (POR) function.

PCA9541A: Product Block Diagram
sot629-1_3d
Data Sheets (1)
Name/DescriptionModified Date
2-to-1 I2C-bus master selector with interrupt logic and reset (REV 5.0) PDF (378.0 kB) PCA9541A24 Apr 2014
Users Guides (3)
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
I2C Demonstration Board 2005-1 Quick Start Guide (REV 1.0) PDF (261.0 kB) UM1020613 Jun 2006
Brochures (1)
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
Package Information (3)
Name/DescriptionModified Date
plastic small outline package; 16 leads; body width 3.9 mm (REV 1.0) PDF (192.0 kB) SOT109-108 Feb 2016
plastic thin shrink small outline package; 16 leads; body width 4.4 mm (REV 1.0) PDF (300.0 kB) SOT403-108 Feb 2016
plastic thermal enhanced very thin quad flat package; no leads; 16 terminals; body 4 x 4 x 0.85 mm (REV 1.0) PDF (200.0 kB) SOT629-108 Feb 2016
Packing (3)
Name/DescriptionModified Date
SO16; Reel pack; SMD, 13" Q1/T1 Standard product orientation Orderable part number ending ,118 or J Ordering... (REV 4.0) PDF (210.0 kB) SOT109-1_11824 Apr 2013
HVQFN16; Reel pack; SMD, 13" Q1/T1 Standard product orientation Orderable part number ending ,118 or... (REV 1.0) PDF (259.0 kB) SOT629-1_11817 Apr 2013
TSSOP16; Reel pack; SMD, 13" Q1/T1 Standard product orientation Orderable part number ending ,118 or... (REV 1.0) PDF (218.0 kB) SOT403-1_11808 Apr 2013
Supporting Information (3)
Name/DescriptionModified Date
Footprint for reflow soldering (REV 1.0) PDF (9.0 kB) SO-SOJ-REFLOW08 Oct 2009
Footprint for wave soldering (REV 1.0) PDF (8.0 kB) SO-SOJ-WAVE08 Oct 2009
Footprint for wave soldering (REV 1.0) PDF (16.0 kB) SSOP-TSSOP-VSO-WAVE08 Oct 2009
Design Support
IBIS Model
Ordering Information
ProductPackage version
Package Information
Product IDPackage DescriptionOutline VersionReflow/Wave SolderingPackingProduct StatusPart NumberOrdering code(12NC)MarkingChemical ContentRoHS / Pb Free / RHFLeadFree Conversion DateEFRIFR(FIT)MTBF(hour)MSLMSL LF
PCA9541ABS/01SOT629-1Reel 13" Q1/T1ActivePCA9541ABS/01,118 (9352 893 61118)41A1PCA9541ABS/01Always Pb-free0.02.05E811
PCA9541ABS/03SOT629-1Reel 13" Q1/T1ActivePCA9541ABS/03,118 (9352 893 62118)41A3PCA9541ABS/03Always Pb-free0.02.05E811
PCA9541APW/01SOT403-1SSOP-TSSOP-VSO-WAVEReel 13" Q1/T1ActivePCA9541APW/01,118 (9352 893 65118)9541A/1PCA9541APW/01Always Pb-free0.02.05E811
Bulk PackActivePCA9541APW/01,112 (9352 893 65112)9541A/1PCA9541APW/01Always Pb-free0.02.05E811
PCA9541APW/03SOT403-1SSOP-TSSOP-VSO-WAVEReel 13" Q1/T1ActivePCA9541APW/03,118 (9352 893 66118)9541A/3PCA9541APW/03Always Pb-free0.02.05E811
Bulk PackActivePCA9541APW/03,112 (9352 893 66112)9541A/3PCA9541APW/03Always Pb-free0.02.05E811
PCA9541AD/01SOT109-1SO-SOJ-REFLOW SO-SOJ-WAVE
SO-SOJ-REFLOW SO-SOJ-WAVE
Reel 13" Q1/T1ActivePCA9541AD/01,118 (9352 893 63118)PCA9541AD/1PCA9541AD/01Always Pb-free0.02.05E811
Bulk PackActivePCA9541AD/01,112 (9352 893 63112)PCA9541AD/1PCA9541AD/01Always Pb-free0.02.05E811
PCA9541AD/03SOT109-1SO-SOJ-REFLOW SO-SOJ-WAVE
SO-SOJ-REFLOW SO-SOJ-WAVE
Reel 13" Q1/T1ActivePCA9541AD/03,118 (9352 893 64118)PCA9541AD/3PCA9541AD/03Always Pb-free0.02.05E811
Bulk PackActivePCA9541AD/03,112 (9352 893 64112)PCA9541AD/3PCA9541AD/03Always Pb-free0.02.05E811
2-to-1 I2C-bus master selector with interrupt logic and reset pca9541a
I2C-bus specification and user manual pca9685pw
I2C-bus specification and user manual pca9685pw
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
Expert mode sample code for PCA9541 PCA9541APW
PCA9541 and PCA9541A IBIS model PCA9541APW
plastic thermal enhanced very thin quad flat package; no leads; 16 terminals; body 4 x 4 x 0.85 mm PCA9633
HVQFN16; Reel pack; SMD, 13" Q1/T1 Standard product orientation Orderable part number ending ,118 or... PCA9633
SOT403-1 LPC812M101JDH16
SSOP-TSSOP-VSO-WAVE LPC1114FDH28
Reel 13" Q1/T1 LPC812M101JDH16
plastic small outline package; 16 leads; body width 3.9 mm NPIC6C596A_Q100
Footprint for reflow soldering NPIC6C596A_Q100
Footprint for wave soldering NPIC6C596A_Q100
SO16; Reel pack; SMD, 13" Q1/T1 Standard product orientation Orderable part number ending ,118 or J Ordering... NPIC6C596A_Q100
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