Analog Devices Inc. ADP3157JR

Overview

ADP3157JR from Analog Devices is a 5-bit programmable synchronous buck controller for Pentium III and AMD-K6 processors, implementing active voltage positioning with ±1% output accuracy over temperature, 1.3 V to 3.5 V digitally set output, dual N-channel gate drive, and integrated crowbar overvoltage protection. It operates in constant off-time current-mode control with CT-programmable frequency and supports VRM 8.2/8.3/8.4 compliance.

For engineers reviewing the ADP3157JR datasheet, ADP3157JR pinout, ADP3157JR application, or ADP3157JR equivalent, key selection considerations include its VID-coded voltage programming, SENSE+/- current sensing architecture, SO-16 package thermal limitations (θJA = 110°C/W), and crowbar trip at +9% to +24% above nominal output voltage.

Technical Context

The ADP3157JR uses a current-mode, constant-off-time control architecture where t_OFF is set by an external capacitor on the CT pin (1.8–3.2 µs typical), enabling stable operation without slope compensation. Its internal 5-bit DAC reads VID0–VID4 inputs to generate a programmable reference between 1.3 V and 3.5 V, while the error amplifier (g_m = 2.2 mmho, BW = 500 kHz) drives the CMP node to regulate SENSE–.

Active voltage positioning dynamically adjusts output voltage vs. load current to optimize transient response-critical for Intel VRM-compliant core supplies. The crowbar function triggers when output exceeds +9% to +24% of programmed voltage, forcing DRIVE2 high to short the output via the low-side MOSFET, releasing at ~50% of nominal output.

Key Specifications

Pinout & Package

ADP3157JR is housed in a 16-lead SOIC (SO-16) package with standard JEDEC MS-012AC footprint (5.3 mm × 10.2 mm, 1.27 mm pitch). Thermal resistance θ_JA = 110°C/W limits continuous power dissipation to ≈330 mW at +70°C ambient.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck controller applications.

Compared with ISL6522CRZ and RT8802AGQW, the ADP3157JR delivers unique active voltage positioning for minimal output capacitance, integrated crowbar for fail-safe overvoltage shutdown, and VRM 8.2–8.4 compliance out-of-the-box-making it optimal for Pentium III/AMD-K6 core supplies where reliability and transient performance are critical.

Availability

ADP3157JR is available at Aetrix Electronics and suitable for desktop PC motherboard designs, VRM module manufacturing, processor evaluation platforms, and industrial embedded CPU power supplies requiring stable component supply and long-term lifecycle support.

Supply support for ADP3157JR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, founded in 1965 and headquartered in Wilmington, MA.

The ADP3157JR belongs to Analog Devices' VRM-compliant power management controller product line, designed specifically for high-efficiency, tightly regulated core supplies in x86 desktop and embedded computing platforms.

FAQ

What is the function of the CT pin on the ADP3157JR?

The CT pin on the ADP3157JR connects to an external capacitor that sets the device's fixed off-time (1.8–3.2 µs typical), directly determining switching frequency in its constant-off-time architecture. A 150 pF capacitor yields ~200 kHz at 2.0 V output; frequency decreases with higher V_OUT or heavier loads due to parasitic losses. The CT pin draws 65 µA when V_OUT is regulated, enabling precise timing control without slope compensation.

How does the ADP3157JR implement active voltage positioning?

The ADP3157JR implements active voltage positioning by using its error amplifier output (CMP pin) to dynamically adjust the current comparator threshold (VT1) in proportion to load current. As load increases, the output voltage sags slightly, causing the error amp to raise VT1-increasing peak inductor current and maintaining optimal voltage positioning for fast transients. This reduces required output capacitance and improves response beyond passive positioning methods.

What happens when all VID pins are left floating on the ADP3157JR?

When all five VID pins (VID0–VID4) are left floating on the ADP3157JR, the internal pull-up resistors (20–30 kΩ) drive them high, resulting in the binary code "11111", which places the ADP3157JR into shutdown mode-disabling DRIVE1 and DRIVE2 outputs, halting switching, and reducing supply current to 140–250 µA. This is a defined safe state per datasheet Table I.

Does the ADP3157JR require external components for overvoltage protection?

No, the ADP3157JR includes fully integrated crowbar overvoltage protection that requires no external components. When output voltage exceeds +9% to +24% of the programmed value, the ADP3157JR forces DRIVE2 high to activate the low-side MOSFET, shorting the output to ground. The crowbar releases automatically when output falls below ~50% of nominal voltage, protecting the CPU without added circuitry.

What is the maximum continuous output current supported by the ADP3157JR?

While the ADP3157JR itself does not deliver current, its control architecture supports continuous output currents up to 19 A in typical VRM 8.2/8.3/8.4 reference designs (e.g., Figure 2), using appropriately rated external N-channel MOSFETs, inductors, and output capacitors. The ADP3157JR's current sense threshold (125–165 mV) and gate drive strength (1 A peak) are optimized for this range, with short-circuit current limited to ~20 A under fault conditions.