Microchip Technology HT19LG-G

Overview

HT19LG-G from Supertex Inc. is a high-voltage electronic line switch IC designed to replace mechanical hook switches in telecom terminal equipment. It features 350V breakdown voltage, ≤18Ω on-state resistance, current limiting via external resistor, 2.3V minimum logic-compatible control, and operates with TPG referenced to GND. It serves as the positive-side line switch in telephone handsets and modem interfaces.

For engineers reviewing the HT19LG-G datasheet, HT19LG-G pinout, HT19LG-G application, or HT19LG-G equivalent, key selection criteria include its 350V line withstand capability, 18Ω R_SW, dual-control inputs (HKS/LS), active-low DP for pulse dialing, and SOIC-8 narrow-body packaging compatible with telecom isolation requirements.

Technical Context

The HT19LG-G integrates a charge pump and logic control block to drive a high-voltage switch between TPG (tip) and TP (output), with GND tied to ring. Its three digital control inputs-HKS (hookswitch sense), LS (logic enable), and DP (dial pulse, active-low)-combine via internal truth table to determine switch state, enabling both mechanical and logic-based off-hook detection.

Current limiting is externally set via resistor between CS and TP, establishing a precise 188–330 mA trip threshold. The device maintains <1.0 ms turn-on/turn-off times at 4.5V TPG and supports operation from 2.3V up to 350V on TPG while sustaining ≤2.0 µA leakage at 100V.

Key Specifications

Pinout & Package

HT19LG-G is housed in an 8-lead SOIC (narrow body), 4.90 × 3.90 mm, 1.27 mm pitch, RoHS-compliant package (–G suffix). Pin 4 is NC; all other pins are electrically functional with defined roles.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar electronic line switch applications.

Compared with HT19LG-G, neither SLB700A-1 nor MAX1393 provides high-voltage line switching, programmable current limiting, or pulse-dial control-making them unsuitable alternatives. True functional equivalents require verified 350 V TPG rating, SOIC-8 telecom-grade packaging, and triple-input logic control per DSFP-HT19.

Availability

HT19LG-G is available at Aetrix Electronics and suitable for telephone handsets, modem line interfaces, fax machine control circuits, and remote meter reading terminals requiring stable component supply across industrial telecom design cycles.

Supply support for HT19LG-G 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

Supertex Inc. was a U.S.-based analog semiconductor company specializing in high-voltage, high-reliability interface ICs before its acquisition by Microchip Technology in 2017.

The HT19LG-G belongs to Supertex's telecom line interface product line, engineered specifically for replacing electromechanical hookswitches in POTS-connected devices while meeting FCC Part 68 and IEC 60950 safety requirements.

FAQ

What is the maximum allowable voltage on the TPG pin of the HT19LG-G?

The HT19LG-G supports a maximum input voltage of +350 V on the TPG pin, as specified in its Absolute Maximum Ratings. This rating allows direct connection to standard telephone line interfaces, including ringing voltage peaks. Operation above this voltage risks permanent damage. The device maintains ≤2.0 µA leakage at 100 V and remains functional up to 290 V per electrical characteristics, but 350 V is the absolute stress limit defined in DSFP-HT19.

How does current limiting work on the HT19LG-G, and what resistor value sets 250 mA?

Current limiting on the HT19LG-G is implemented via an external resistor between CS and TP pins. Per the datasheet, a 200 Ω ±1% resistor sets the nominal current limit to 250 mA. The actual trip threshold ranges from 188 mA to 330 mA depending on resistor tolerance and process variation. This feature protects downstream circuitry during short-circuit or overload events on the telephone line, and is independent of TPG voltage within operating range.

Can the HT19LG-G be used with 3.3 V logic control signals?

Yes, the HT19LG-G fully supports 3.3 V logic levels. Its LS and DP inputs accept VIH(HKS) up to VTPG and specify VIH(LS)/VIH(DP) ≥1.5 V, with VIL ≤0.2 V. At 3.3 V, LS asserts high to enable the switch, and DP asserts low to disable it-both within guaranteed operating margins. No level-shifting circuitry is required, simplifying integration with modern low-voltage microcontrollers in modem or VoIP gateway designs.

Is external Zener protection required on the TP pin of the HT19LG-G?

Yes, external Zener protection is mandatory on the TP pin. Although the HT19LG-G specifies VTP max = +18 V, the datasheet explicitly states "Zener protection to prevent this output from rising above 18 V is required." This is because internal clamping alone is insufficient for sustained overvoltage transients. A properly rated Zener diode (e.g., 18 V, 1 W) must be placed between TP and GND to ensure compliance with telecom surge immunity standards and prevent latch-up or failure.

What is the function of the NC pin (Pin 4) on the HT19LG-G?

Pin 4 of the HT19LG-G is designated NC (No Connect) and has no internal connection. It must remain unconnected on the PCB layout-neither tied to GND, VCC, nor left floating in a way that compromises creepage distance. The SOIC-8 package outline confirms this pin is not bonded. Routing traces or placing vias under Pin 4 is acceptable only if it does not reduce minimum clearance to adjacent pins, especially given the 350 V TPG requirement.