Analog Devices Inc. LTC1556IGN#TRPBF

Overview

LTC1556IGN#TRPBF from Analog Devices (formerly Linear Technology) is a SIM power supply and level translator IC for GSM cellular telephone interfaces. It integrates a step-up/step-down charge pump delivering programmable 3V or 5V VCC output (±5% regulation), 3V–5V bidirectional signal level translation for CLK/RST/I/O/DATA, >10kV HBM ESD protection on all SIM-contact pins, and an auxiliary 4.3V LDO/power switch - all in a 20-pin narrow SSOP package.

For engineers reviewing the LTC1556IGN#TRPBF datasheet, LTC1556IGN#TRPBF pinout, LTC1556IGN#TRPBF application, or LTC1556IGN#TRPBF equivalent, key selection considerations include its dual-mode VCC programming (3V/5V/VIN), soft-start-controlled inrush current limiting, shutdown current <1µA, 650kHz charge pump frequency, and integrated LDO functionality exclusive to the LTC1556 variant.

Technical Context

The LTC1556IGN#TRPBF implements a gated-switch charge pump architecture that operates as a voltage doubler when VIN < VCC and as a step-down converter when VIN > VCC, enabling stable 3V or 5V output across a 2.7V–10V input range. Its level-shifting circuitry uses internal pull-up resistors (10kΩ on I/O, 20kΩ on DATA) and open-drain drivers to translate between DVCC (1.8V–5.5V) controller logic and SIM-side VCC-referenced signals.

Unlike the LTC1555, the LTC1556IGN#TRPBF includes an auxiliary LDO section with EN/FB/LDO pins: FB tied to LDO yields regulated 4.3V (±0.25V) at up to 10mA; FB grounded or floating configures LDO as a ≤30Ω switch to VCC. This LDO is only active when VCC ≥ 5V and draws current from the VCC rail.

Key Specifications

Pinout & Package

Package: 20-lead narrow SSOP (GN20), 0.150" body width, RoHS-compliant, moisture-sensitive level 3.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar SIM power supply and level translation applications.

Compared with LTC1556CGN, the LTC1556IGN#TRPBF offers guaranteed operation over –40°C to 85°C and tape-and-reel packaging for automated assembly; compared with LTC1555IGN#TRPBF, it adds a configurable 4.3V LDO or VCC switch - critical for powering noise-sensitive RF synthesizers in GSM transceivers.

Availability

LTC1556IGN#TRPBF is available at Aetrix Electronics and suitable for GSM handset design, smart card reader development, secure identity module integration, and IoT eSIM power management requiring stable component supply across industrial temperature ranges and long production lifecycles.

Supply support for LTC1556IGN#TRPBF 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 acquired Linear Technology in 2017 and maintains full product support, datasheets, and application engineering for legacy Linear parts including the LTC series.

The LTC1556IGN#TRPBF belongs to Linear's SIM interface power management product line, designed specifically to simplify 3V controller-to-5V SIM connectivity in space-constrained, battery-operated wireless devices.

FAQ

What is the maximum output current capability of the LTC1556IGN#TRPBF at 5V VCC output?

The LTC1556IGN#TRPBF delivers up to 10mA continuous output current when VIN ≥ 2.7V, and up to 20mA when VIN ≥ 3V - sufficient for standard ISO/IEC 7816-3 SIM cards operating at 5V. The actual available current decreases slightly under heavy load due to charge pump efficiency losses and internal LDO current draw when enabled. For sustained 20mA loads, VIN must remain ≥3V and thermal conditions must stay within the 85°C junction limit.

How does the soft-start feature of the LTC1556IGN#TRPBF reduce inrush current during power-up?

The LTC1556IGN#TRPBF limits inrush current to approximately 25mA (with COUT = 10µF) when the SS pin is held low, by controlling the charge pump's effective duty cycle during initial turn-on. This prevents voltage droop on shared 3V DC/DC rails - a common cause of microcontroller resets in GSM handsets. When SS is high, VCC ramps in ≤1ms without current limiting, enabling fast SIM initialization where supply stability is assured.

Can the LTC1556IGN#TRPBF be used with a 3V SIM card, and how is the output voltage configured?

Yes, the LTC1556IGN#TRPBF supports 3V SIM cards via its programmable VCC output. Setting M0 = DVCC and M1 = 0V configures the charge pump for regulated 3V output (2.8V–3.2V). This mode maintains tight regulation across the full 2.7V–10V VIN range and draws only 60µA quiescent current - making it ideal for dual-voltage SIM compatibility in global handset designs.

What is the purpose of the EN and FB pins on the LTC1556IGN#TRPBF, and how do they affect the LDO function?

The EN pin enables or disables the auxiliary LDO section: high = active, low = off (LDO floats or sinks to GND). The FB pin selects operating mode - tied to LDO yields regulated 4.3V output; grounded or floating configures LDO as a ≤30Ω switch to VCC. Critically, the LDO only functions when VCC ≥ 5V; it is disabled during 3V VCC operation. This ensures correct power sequencing in GSM RF sections.

Does the LTC1556IGN#TRPBF require external components beyond capacitors, and what are their values?

The LTC1556IGN#TRPBF requires only three external capacitors: a 10µF low-ESR ceramic or tantalum capacitor on VIN, a 10µF low-ESR capacitor on VCC, and a 0.1µF ceramic flying capacitor between C1+ and C1−. No inductors, resistors, or feedback networks are needed. These values ensure stable regulation, minimal output ripple (<75mVP-P), and reliable ESD performance - matching the reference design in Linear's datasheet Figure TA02.