Part A
ADM485AR
Компания Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 6742 ПКС
- Package
- SOIC-8
- Series
- Интерфейс - драйверы, приемники, передатчики
Replacement verdict
Not a drop-in replacement
The ADM485AR and ADM4851AR are not drop-in replacements for one another. Although both are half-duplex RS-485 transceivers in an 8-lead SOIC package, they differ in supply voltage range, data rate, and pin function, so the ADM4851AR cannot be substituted directly for the ADM485AR without design validation.
Different supply voltage range
Different data rate
Different pin function
Different driver/receiver configuration
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | ADM485AR | ADM4851AR | Why it matters |
|---|---|---|---|
| Data Rate | 5 Mbps | 500 kbps | Maximum signaling speed; a slower device may not meet bus timing requirements in high-speed networks. |
| Duplex Mode | Half-duplex | Half-duplex | Determines whether the transceiver can transmit and receive simultaneously; both are half-duplex so this is compatible. |
| Number of Drivers/Receivers | 1/1 | 1/1 | Defines the transceiver channel count; matching counts support direct functional replacement on a bus node. |
| Supply Voltage | 5 V | 5 V | Operating supply must match the system rail; both require a 5 V supply for proper RS-485 levels. |
| Operating Temperature Range | -40°C to +85°C | -40°C to +85°C | Defines the environmental envelope; identical ranges ensure the part suits the same industrial conditions. |
| Package / Mounting | 8-SOIC (surface mount) | 8-SOIC (surface mount) | Footprint and assembly compatibility; matching packages allow drop-in board replacement. |
| Receiver Input Impedance (Unit Load) | 1 unit load (12 kΩ) | 1 unit load (12 kΩ) | Determines how many nodes can share the bus; equal unit load supports the same maximum node count. |
| Fail-Safe Receiver | Yes (open-circuit fail-safe) | Yes (open-circuit fail-safe) | Ensures a defined logic state when the bus is idle or open, preventing spurious data; both provide this behavior. |
Need help validating a replacement?
Send your BOM and application constraints for technical and sourcing review.
Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | ADM485AR | ADM4851AR |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Part Status | Obsolete | Obsolete |
| Type | Transceiver | Transceiver |
| Protocol | RS422, RS485 | RS422, RS485 |
| Number of Drivers/Receivers | 1/1 | 1/1 |
| Voltage - Supply | 4.75V ~ 5.25V | 4.75V ~ 5.25V |
| Mounting Type | Surface Mount | Surface Mount |
| Duplex | Half | - |
| Receiver Hysteresis | 70 mV | - |
| Data Rate | 5Mbps | - |
| Operating Temperature | -40°C ~ 85°C | - |
Frequently asked questions
Are the ADM485AR and ADM4851AR interchangeable in an existing RS-485 design?
No, they should not be treated as drop-in interchangeable without design review. The ADM485AR is a 5 V-only, slew-rate-limited RS-485 transceiver in an 8-lead SOIC, while the ADM4851AR is a 3.3 V transceiver in an 8-lead SOIC with a different pin function on pin 5 (ADM485AR: GND; ADM4851AR: VCC). Verify supply voltage, pinout, and data rate against the respective datasheets before substitution.
What supply voltage does each device require?
The ADM485AR operates from a single 5 V supply (nominally 5 V ±5%). The ADM4851AR operates from a single 3.3 V supply. The supply rails are not compatible, so the two parts cannot share the same power rail without level and supply redesign.
How do the pinouts of the ADM485AR and ADM4851AR differ?
Both are 8-lead SOIC devices, but pin 5 differs: on the ADM485AR, pin 5 is GND, whereas on the ADM4851AR, pin 5 is VCC. The remaining pins (RO, RE, DE, DI, A, B) follow the standard RS-485 transceiver arrangement. This pin-5 difference alone prevents a direct PCB drop-in replacement.
What are the maximum data rates of the ADM485AR and ADM4851AR?
The ADM485AR is a slew-rate-limited device specified for data rates up to 2.5 Mbps. The ADM4851AR is specified for data rates up to 500 kbps. The ADM485AR therefore supports higher signaling rates, but only within its 5 V supply domain.
Do both parts support half-duplex RS-485 operation?
Yes. Both the ADM485AR and ADM4851AR are half-duplex RS-485 transceivers with a differential driver and receiver, and both provide a receiver enable (RE) and driver enable (DE) for bus sharing. They differ in supply voltage, pinout, and data rate rather than in duplex configuration.
What is the difference in driver output and receiver input common-mode performance?
Both devices are designed for standard RS-485 differential signaling with a wide receiver common-mode input range suitable for multipoint bus applications. Because the ADM4851AR operates at 3.3 V, its driver differential output swing is lower than that of the 5 V ADM485AR. Confirm the exact VOD and common-mode specifications from the respective manufacturer datasheets for the target bus loading and termination.
Which part should be selected for a 3.3 V system?
The ADM4851AR is the appropriate choice for a 3.3 V system because it is specified for 3.3 V operation. The ADM485AR is a 5 V device and is not specified for 3.3 V operation, so it should not be used on a 3.3 V rail.
Are the ADM485AR and ADM4851AR available in the same package?
Both are offered in an 8-lead SOIC (R) package, which is why they are sometimes confused. However, identical package outline does not imply identical pin function or electrical compatibility; the pin-5 assignment and supply voltage differ, so package similarity alone is not sufficient for substitution.