Renesas ISL9491ERZ

Overview

ISL9491ERZ 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 datasheet, ISL9491ERZ pinout, ISL9491ERZ application, or ISL9491ERZ equivalent, key selection considerations include its QFN-16 package, 22kHz tone modulation capability, VSET0/VSET1 logic-controlled output voltage selection, integrated overcurrent/overtemperature protection, and compatibility with single-tuner/single-dish LNB power architectures.

Technical Context

The ISL9491ERZ employs a current-mode boost PWM (380–480kHz) feeding a linear post-regulator to minimize power dissipation while maintaining precise output regulation. Its VSW-to-VOUT dropout is dynamically adjusted to ~1.2V at 500mA, enabling efficient operation across varying input (8–14V) and load conditions.

It implements dual-stage protection: pulse-by-pulse CS pin overcurrent limiting for the boost FET, and programmable dynamic current limiting (50ms ON / 900ms OFF) via ILIMIT resistor, plus thermal shutdown at 130°C with 20°C hysteresis. The EXTM pin accepts external 22kHz DiSEqC tone and symmetrically injects it onto VLNB with 5–15µs rise/fall times.

Key Specifications

Pinout & Package

ISL9491ERZ is housed in a 4mm × 4mm, 16-lead QFN package (Pb-free, RoHS-compliant, JEDEC MO-220 variant L16.4x4) with exposed thermal pad for efficient heat transfer. Pin 1 is marked by an index area in the top-left corner of the package.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX22000AETL+ and LM3481MM/NOPB, the ISL9491ERZ uniquely combines analog VSET-based voltage selection, hardware 22kHz tone injection, and integrated linear regulation in a single QFN package-making it optimal for cost-sensitive, high-volume satellite STB designs requiring DiSEqC 1.x and SWM compliance without microcontroller dependency.

Availability

ISL9491ERZ is available at Aetrix Electronics and suitable for satellite set-top box, personal video recorder, and DIRECTV SWM receiver applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for ISL9491ERZ 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 (now part of Renesas Electronics) is a leader in precision analog and power management ICs, serving industrial, infrastructure, and high-end consumer markets with high-reliability solutions.

The ISL9491ERZ belongs to Intersil's satellite power management product line, engineered specifically for low-noise, high-efficiency LNB biasing in single-tuner satellite reception systems with DiSEqC and SWM protocol support.

FAQ

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

The ISL9491ERZ supports four output voltages: 13.3V, 14.3V, 18.3V, and 20.0V (typical). Selection is achieved using the logic states of VSET0 and VSET1 pins, which have internal 200kΩ pull-down resistors. For example, VSET1 = 0 and VSET0 = 0 configures 13.3V output. This enables direct hardware control of LNB polarization without MCU intervention. The ISL9491ERZ datasheet Table 1 defines all combinations precisely.

Does the ISL9491ERZ support DiSEqC 2.x, or only DiSEqC 1.x?

The ISL9491ERZ natively supports DiSEqC 1.x via its EXTM pin, which accepts and symmetrically transfers 22kHz tone signals to VLNB. For DiSEqC 2.x, an external tank circuit (inductor + capacitor) must be added at the EXTM pin per the datasheet recommendation. The ISL9491ERZ itself does not integrate DiSEqC 2.x encoding logic but provides the analog signal path required for full protocol implementation.

How is overcurrent protection implemented on the ISL9491ERZ?

The ISL9491ERZ implements two-tier overcurrent protection: (1) pulse-by-pulse limiting on the boost FET via the CS pin (trip at ~445mV), and (2) programmable dynamic current limiting via the ILIMIT pin. A resistor from ILIMIT to GND sets the LDO current threshold (e.g., 148kΩ → 350mA); exceeding this for 50ms triggers 900ms shutdown cycles. Static limiting (750mA constant) is possible with 0Ω at ILIMIT, but thermal shutdown will activate under sustained overload.

What is the purpose of the TCAP pin on the ISL9491ERZ, and how does it affect startup?

The TCAP pin on the ISL9491ERZ sets the soft-start time for the output voltage using an external capacitor. A 0.22µF capacitor yields ~13ms rise time; 0.44µF extends it to ~32ms. This controls inrush current and prevents overshoot during power-up. A 10kΩ series resistor is recommended to filter switching noise from coupling into TCAP. The ISL9491ERZ uses TCAP voltage as a reference for the ramp generator, making capacitor tolerance critical for timing accuracy.

Can the ISL9491ERZ be used in DIRECTV SWM systems, and what ensures compliance?

Yes, the ISL9491ERZ is explicitly stated as DIRECTV SWM compliant in its datasheet. Compliance is ensured by its ability to generate spectrally clean 22kHz tone bursts with precise amplitude (400–900mV p-p), fast edges (5–15µs), and accurate timing alignment relative to EN assertion. Its integrated architecture eliminates external tone-generation components, reducing jitter and ensuring consistent SWM signal integrity required for reliable multiswitch communication.