PCA9557DR - 8-Bit I2C/SMBus I/O Expander with Reset | TI
N.º da peça: PCA9557DR ✓ Ativo| Qtd. | Preço unitário | Total |
|---|---|---|
| 1 | $1.42 | $1,42 |
| 10 | $1.18 | $11,80 |
| 100 | $0.96 | $96,00 |
| 500 | $0.82 | $410,00 |
| 1.000 | $0.71 | $710,00 |
PCA9557DR Visão geral
An I/O expander is a type of digital interface IC that sits on an I2C/SMBus and exposes additional GPIO to a host processor that has too few pins for its application. It belongs to the broader family of parallel-port expanders and, hierarchically, to peripheral ICs > interface ICs > digital logic ICs. Compared to a discrete shift-register approach, an I2C expander uses fewer host pins (only SCL and SDA), supports multi-drop addressing on the bus, and consumes very low standby current.
Key features of the PCA9557DR include 1 uA maximum standby current, 5 V tolerant I/O, hardware reset via the RESET pin, software reset through the I2C general-call address, and individually configurable I/O direction. The device supports up to eight slave addresses set by A0-A2 (within the PCA9557 family address space) so multiple expanders can share a single bus. An interrupt output (INT) signals the host when any input changes state, avoiding polling overhead.
The PCA9557DR uses a CMOS process with internal power-on reset and a low-impedance output structure capable of sourcing/sinking 10 mA per bit at 5 V, enabling direct LED drive in many cases. SMBus-alert and hardware-pin reset combine for robust multi-device control. According to the TI PCA9557 datasheet (SCPS155D-family), the device is pin-compatible with the PCA9554/PCA9534/PCF8574 series in 16-pin SOIC.
Typical applications include server chassis management, industrial control panels, portable instrumentation, ACPI GPIO expansion on motherboards, keypad scanning, and LED driving on plug-in cards. Designers choose it when they need to expand a microcontroller's GPIO count over I2C while maintaining low standby power.
When designing with this device, always include pull-up resistors on SCL, SDA, RESET, and INT per the I2C/SMBus specification (typically 2.2 k to 10 k depending on bus capacitance and speed). Decouple VCC with a 0.1 uF ceramic capacitor placed within 5 mm of the supply pin to suppress switching transients.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet, giving buyers a one-stop comparison source.
Alternativas drop-in para PCA9557DR — mesmo encapsulamento, compatível pino a pino. Peças de encapsulamento diferente que exigem retrabalho na PCB são excluídas.
Ferramenta de comparação rápida — selecione peças alternativas para comparação lado a lado:
PCA9557DTG4
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCA9534DR
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCA9554DR
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCA9670DR
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCF8574DR
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCA9557DR Especificações
| Number of I/O Bits | 8 |
| Interface | I2C, SMBus |
| Bus Frequency (Max) | 400 kHz |
| Supply Voltage (VCC) | 2.3 V to 5.5 V |
| Temperatura de operação | -40 C to +85 C |
| Standby Current (Max) | 1 uA |
| I/O Voltage Tolerance | 5.5 V tolerant |
| Reset Input | Active-low hardware RESET + software reset (general call) |
| Interrupt Output (INT) | Yes, open-drain |
| Slave Address Pins | A0, A1, A2 (3 pins, 8 addresses within family) |
| Encapsulamento | 16-SOIC (DR, 7.5 mil pitch) |
| Tipo de montagem | Surface Mount |
| Nível MSL | 1 (unlimited floor life) |
| Status RoHS | Compliant |
| Lead-Free | Yes |
| Configuration Registers | Input/output direction registers, polarity inversion |
Configuração de pinos do PCA9557DR
| Pino 1 | A0 — I2C slave address select bit 0 |
| Pino 2 | RESET — Active-low hardware reset input |
| Pino 3 | P0 — GPIO bit 0 (bidirectional) |
| Pino 4 | P1 — GPIO bit 1 (bidirectional) |
| Pino 5 | P2 — GPIO bit 2 (bidirectional) |
| Pino 6 | P3 — GPIO bit 3 (bidirectional) |
| Pino 7 | VCC — Positive supply voltage (2.3 V to 5.5 V) |
| Pino 8 | NC — Not connected (per datasheet) |
| Pino 9 | SCL — I2C serial clock input |
| Pino 10 | SDA — I2C serial data (bidirectional) |
| Pino 11 | INT — Interrupt output (open-drain, active-low) |
| Pino 12 | P4 — GPIO bit 4 (bidirectional) |
| Pino 13 | P5 — GPIO bit 5 (bidirectional) |
| Pino 14 | P6 — GPIO bit 6 (bidirectional) |
| Pino 15 | P7 — GPIO bit 7 (bidirectional) |
| Pino 16 | GND — Ground reference |
Aplicações típicas
PCA9557DR é adequado para 6 aplicaçãos: Server Chassis Management GPIO, Industrial PLC I/O Expansion, Portable Instrumentation Key Scanning, ACPI GPIO Expansion on Motherboards, LED Driving on Plug-in Cards, Home Appliance User Interface.
Server Chassis Management GPIO
The PCA9557DR is widely used to expand host BMC GPIO for chassis intrusion switches, fan tachometers, and LED indicators on server motherboards. Its 2.3-5.5 V supply and 5.5 V tolerant I/O tolerate both 3.3 V and 5 V backplane logic levels, while the 400 kHz I2C speed keeps bus traffic low. The hardware RESET pin enables deterministic bring-up after hot-plug events, and the open-drain INT output signals the BMC whenever an input changes state without polling. This combination is why PCA9557-family parts are specified on most ATX/microATX server designs.
Recomendado
Industrial PLC I/O Expansion
Factory automation controllers use PCA3580-expander variants to bring 24 V-tolerant digital I/O onto a low-voltage MCU bus through external level shifters. The PCA9557DR's 1 uA standby current suits PLC modules that spend long idle periods. Its hardware RESET pin is critical in industrial environments where brownouts and ESD events can latch the bus, and its INT pin enables event-driven control loops instead of costly register polling.
Recomendado
Portable Instrumentation Key Scanning
Handheld test gear and medical monitors rely on the PCA9557DR to scan matrix keypads and toggle LEDs without consuming host MCU pins. Its 1 uA standby current extends battery life, and its small 16-SOIC footprint leaves PCB area for analog front-end components. The hardware RESET allows the host to recover from firmware hangs without power cycling, and the INT pin generates an immediate interrupt on any key-press transition.
Recomendado
ACPI GPIO Expansion on Motherboards
Laptop and desktop platforms frequently assign a PCA9557DR to expand the EC's GPIO count for case-open detection, lid switch, sleep button, and other ACPI events. The 2.3-5.5 V operation aligns with typical S0/S5 rail voltages, and the INT pin routes directly to the EC's interrupt controller. Hardware RESET ensures that after G3->S5 transitions the expander returns to a known state before the EC begins enumerating it.
Recomendado
LED Driving on Plug-in Cards
Network cards, RAID controllers, and graphics cards use the PCA9557DR to drive front-panel status LEDs directly from the I2C bus. With 10 mA sink/source capability per pin (per TI datasheet), the expander can drive small indicator LEDs without external transistors. Eight selectable slave addresses let designers stack multiple cards without address conflicts on a shared SMBus.
Recomendado
Home Appliance User Interface
Washing machines, dishwashers, and coffee makers use the PCA9557DR to multiplex front-panel buttons and 7-segment displays from a single MCU. The 1 uA standby current supports Energy Star idle requirements, and the hardware RESET allows recovery from line-voltage glitches common in white-goods power environments. The 8 GPIO are sufficient for 4-7 keypad buttons plus 1-2 status LEDs.
Recomendado
Resumo dos produtos recomendados
Dados de referência de engenharia para PCA9557DR — comparação, orientação de projeto e informações de conformidade.
Guia de seleção
Comparação com alternativas
| Parâmetro | Este produto | PCA9557DTG4 | PCA9534DR | PCA9554DR | PCA9670DR | PCF8574DR |
|---|---|---|---|---|---|---|
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | NXP Semiconductors | Texas Instruments |
| Package | 16-SOIC (DR) | 16-SOIC - same | 16-SOIC - same | 16-SOIC - same | 16-SOIC - same | 16-SOIC - same |
| Number of I/O | 8 | 8 | 8 | 8 | 8 | 8 |
| Max I2C Clock | 400 kHz | 400 kHz | 400 kHz | 400 kHz | 1 MHz | 400 kHz |
| Supply Voltage | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 2.5 V to 6.0 V |
| Hardware RESET Pin | Yes (active-low) | Yes | No | No (software reset only) | No | No |
| INT Output | Yes (open-drain) | Yes | Yes | Yes | Yes | No (INT output absent) |
Principais diferenciais
- Dedicated hardware RESET pin (vs PCA9534DR / PCA9554DR)
- Higher 1 MHz I2C capability on cross-brand alternative (vs PCA9670DR (NXP))
- Lower standby current than PCF8574 family (vs PCF8574DR)
Notas de projeto
Decouple VCC with a 0.1 uF X7R ceramic capacitor placed within 5 mm of the SOIC pin 7. For multi-expander SMBus designs, add a 10 uF bulk capacitor near the bus entry point to handle simultaneous switching transients from multiple INT and LED outputs. The 1 uA max standby current means supply-rail leakage is negligible compared to bus pull-up resistor currents.
Place the PCA9557DR close to the host MCU to keep the I2C bus short (< 10 cm if possible) and minimize capacitive loading. Route SCL and SDA as a differential pair with matched length, and keep them away from switching power traces and clock signals. The INT trace can be routed like any other digital signal but should not cross high-dV/dt traces without a ground-guard trace.
Do not leave the RESET pin floating - it MUST be tied to VCC through a pull-up resistor (typically 10 k) if not driven by a host GPIO. Floating RESET can cause intermittent I2C bus lockups at power-up. Also note that pin 8 is NC; do not connect it to any signal, as it can inject noise into the internal bandgap reference. Verify pull-up resistor values for SCL/SDA/INT: too weak and rise time violates the 400 kHz spec; too strong and pull-down drive fights the expander's 20 mA sink.
Informações de conformidade
RoHS and REACH compliant per TI product page. Lead-free (Pb-free) SOIC package with matte-tin plating. Halogen-free per TI 2015 declaration. Not AEC-Q100 qualified - choose automotive-grade variant for vehicle applications.
