Renesas ISL9491ERZ-T

Overview

ISL9491ERZ-T from Intersil is a single-output LNB supply voltage regulator IC designed for satellite set-top box applications. It integrates a current-mode boost converter and low-noise linear regulator with tone injection, DiSEqC 1.x/2.x support, and pin-controllable polarization selection (13.3V/14.3V/18.3V/20.0V). It delivers up to 500mA continuous output with <1.4V dropout and supports DIRECTV SWM compliance.

For engineers reviewing the ISL9491ERZ-T datasheet, ISL9491ERZ-T pinout, ISL9491ERZ-T application, or ISL9491ERZ-T equivalent, key selection considerations include LNB polarization voltage programming via VSET0/VSET1, external DiSEqC tone injection on EXTM, fault reporting via open-drain FAULT, soft-start control via TCAP capacitor, and thermal shutdown at 130°C.

Technical Context

The ISL9491ERZ-T employs a two-stage architecture: a high-efficiency (>92%) current-mode boost PWM (440kHz typical) supplies regulated input to an internal linear post-regulator, minimizing power dissipation by maintaining constant ~1.2–1.4V dropout across the pass element. The VSW pin receives boosted voltage, while VOUT drives the anode of the back diode and VSENSE connects to its cathode - enabling safe operation with up to 24V reverse bias tolerance.

Control logic includes EN-driven enable/disable, VSET0/VSET1-selectable output voltages per Table 1, and EXTM-pin-based symmetric DiSEqC tone modulation (22kHz for ISL9491). Fault detection covers undervoltage, overvoltage (±12%), linear overcurrent, and overtemperature (130°C shutdown), all asserted on the open-drain FAULT pin.

Key Specifications

Pinout & Package

ISL9491ERZ-T uses a 16-lead QFN package (4mm × 4mm, L16.4x4), thermally enhanced with exposed pad. Pin numbering follows top-view orientation with pin 1 index area in top-left corner.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LNB supply regulator applications.

Compared with ISL9491AERZ-T and MAX22000AETL+, the ISL9491ERZ-T provides optimal balance of analog integration, DiSEqC 22kHz compliance, and cost efficiency for mainstream consumer STBs - whereas ISL9491AERZ-T serves niche legacy designs and MAX22000AETL+ targets high-end programmable infrastructure.

Availability

ISL9491ERZ-T is available at Aetrix Electronics and suitable for satellite set-top box, personal video recorder, and DIRECTV SWM-compatible device manufacturing requiring stable component supply, consistent parametric performance, and long-term production continuity.

Supply support for ISL9491ERZ-T 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

Intersil Corporation is a leading provider of precision analog and power management ICs, now part of Renesas Electronics, with deep expertise in satellite, broadcast, and consumer power solutions.

The ISL9491ERZ-T belongs to Intersil's LNB power management product line, engineered specifically for high-efficiency, low-noise, and standards-compliant satellite receiver front-end power delivery.

FAQ

What output voltages does the ISL9491ERZ-T support, and how are they selected?

The ISL9491ERZ-T supports four output voltages: 13.3V, 14.3V, 18.3V, and 20.0V (typical), corresponding to common LNB polarization requirements. Selection is achieved via binary logic on VSET0 and VSET1 pins per Table 1 in the datasheet. For example, VSET1=0/VSET0=0 yields 13.3V for vertical polarization, while VSET1=0/VSET0=1 selects 18.3V for horizontal. All combinations are internally trimmed and require no external feedback resistors - the ISL9491ERZ-T implements this entirely within its analog control loop.

How does the ISL9491ERZ-T handle DiSEqC tone injection, and what is the required input signal format?

The ISL9491ERZ-T accepts a 22kHz square wave on the EXTM pin with 50% duty cycle, V_H=2.5V, V_L=0V, and rise/fall times ≤15µs. It transfers this tone symmetrically onto the VLNB output line to meet DiSEqC 1.x specifications. The IC includes internal shaping circuitry to preserve tone fidelity and suppress harmonics. No external tank circuit is needed for DiSEqC 1.x, though one may be added for DiSEqC 2.x support - the ISL9491ERZ-T remains fully functional in either configuration.

What is the purpose of the VOUT and VSENSE pins, and why are both required?

VOUT drives the anode of the back diode in series with the LNB, while VSENSE connects to the cathode - forming a Kelvin-sense configuration that rejects voltage drop across the diode and PCB traces. This ensures accurate regulation at the LNB input despite forward voltage variation (0.3–0.5V) and trace resistance. VSENSE also withstands up to 24V reverse bias, protecting the IC when the LNB is disconnected or back-fed. Using both pins is mandatory for stable operation; omitting VSENSE causes regulation failure and FAULT assertion.

Can the ISL9491ERZ-T be used without an external boost inductor and FET?

No - the ISL9491ERZ-T requires an external boost inductor (e.g., 10µH), Schottky diode (e.g., B230A), and N-channel MOSFET (driven by GATE) to form the complete boost stage. The IC contains only the controller, current sense amplifier, and linear regulator. Its architecture depends on the external boost to generate sufficient VSW voltage for the LDO to maintain low dropout. Operating without these components results in no regulated output and potential damage due to uncontrolled VSW voltage.

How does the FAULT pin behave during normal operation versus fault conditions?

During normal operation (output in regulation, no overtemp/overcurrent), the FAULT pin remains high-impedance and must be pulled up externally (e.g., 10kΩ to 3.3V). It asserts low only during specific faults: output voltage outside ±12% window, junction temperature >130°C, linear overcurrent exceeding programmed ILIMIT threshold, or VCC below UVLO threshold (4.4V). FAULT stays latched low until the fault clears and a full soft-start cycle completes - it does not pulse or auto-recover during transient events unless the root cause is removed.