High-performance, small-package logic-level conversion for smartphones

1 Introduction

In the past one or two years, driven by Apple's iPhone, the smartphone market has expanded rapidly. An important feature of portable products such as smartphones is that they have more and more functions, thus supporting a wider range of consumer needs. However, the operating voltages of ICs or modules used to support different functions in portable products such as smartphones are often different. For example, the voltage of baseband processors and application processors is generally between 1.5 V and 1.8 V, while many existing peripherals generally operate at 2.6 V to 3.3 V, such as USIM cards, Wi-Fi modules, and FM tuner modules, which operate at 2.8 V, and camera modules, which operate at 2.7 V.

Figure 1 Logic level converter application diagram

Therefore, there is an input/output voltage mismatch problem between different ICs and peripheral modules in portable products such as smartphones. To enable these devices and modules to communicate with each other, efficient logic voltage level conversion is required. The so-called logic level converter connects ICs and modules or printed circuit boards (PCBs) with different operating voltages to provide system integration solutions.

2 Traditional logic level conversion methods and their advantages and disadvantages

Since transistor-transistor logic (TTL) and complementary metal oxide semiconductor (CMOS) are standard levels in logic circuits, TTL-CMOS input conversion is very common in traditional logic level conversion methods. This conversion method is simple and low-cost, and is mainly used for low-level to high-level conversion, and can also be used to convert high-level to low-level. This conversion method has some disadvantages. Other traditional logic level conversion methods include overvoltage tolerance (OVT) voltage conversion, open drain (OD)/active pull-down conversion, and discrete I2C conversion, each with its own advantages and disadvantages, see Table 1.

[page] Table 1 Traditional logic level conversion methods and their advantages and disadvantages

3 Dual power supply logic level conversion and application

Power is consumed in logic level conversion. For example, in low-to-high level conversion, in order to output a high logic level, the input voltage (Vin) is lower than VCC, and the power supply current change (ΔICC) is always high, so the power consumption is also high. To solve the problem of high power consumption, a dual power supply voltage (VCCA and VCCB) logic level converter can be used. When the logic power supply voltage (VL) is equal to Vin, ΔICC is 0, thereby reducing power consumption.

Common dual-supply logic level conversions include unidirectional conversion, bidirectional conversion with direction control pins, automatic sensing bidirectional conversion (push-pull output), and automatic sensing bidirectional conversion for open-drain applications (such as I2C). The structural diagram is shown in Figure 2.

Figure 2 Schematic diagrams of the structures of several dual-supply logic level converters:

(a) Unidirectional logic level converter; (b) Bidirectional logic level converter with direction control pin; (c) Auto-sensing bidirectional logic level converter; (d) Auto-sensing bidirectional logic level converter for open-drain applications (such as I2C)

Among these dual-power supply logic level conversion methods, the principle of unidirectional logic level conversion is to provide conversion from point A to point B when the output enable (Output Enable,) is low; when the output enable is high, A and B are in a high impedance state (Hi-Z), which is usually treated as infinite resistance, equivalent to no connection. Common dual-power supply unidirectional logic level converters include ON Semiconductor's NLSV1T34AMX1TCG, NLSV2T244MUTAG, NLSV4T3234FCT1G, NLSV8T244MUTAG, NLSV22T244MUTAG, etc. The applications of these dual-power supply unidirectional logic level converters include general-purpose input and output (GPIO) ports, serial peripheral interface (SPI) ports, and universal serial bus (USB) ports.

The working principle of the bidirectional logic level converter with direction control pin is: when the pin and the direction control (DIRection, T/) pin are both low, it provides point B to point A conversion; when the pin is low and the T/ pin is high, it provides point A to point B conversion; and when the pin is high, the direction from point A to point B and the direction from point B to point A are both in high impedance state, which is equivalent to no connection. ON Semiconductor is about to launch a bidirectional logic level converter with direction control pin. Common applications of this type of converter are memory and I/O devices that are accessed by byte.

The working principle of the automatic sensing bidirectional logic level converter (push-pull output) is: when the enable (EN) pin is low, the converter is in standby state; when the EN pin is high and the I/O level does not change, the converter is in steady state; when the EN pin is high and the I/O level changes, the converter detects the change and generates a pulse, and the I/O is pulled up to faster by the P-channel MOSFET (PMOS). Typical automatic sensing direction bidirectional logic level converters (push-pull output) are NLSX3012MUTAG, NLSX3013FCT1G, NLSX3013BFCT1G, NLSX4014MUTAG and NLSX3018MUTAG from ON Semiconductor. Common applications of this type of converter include universal asynchronous receiver and transmitter (UART), USB port, 4-wire SPI port and 3-wire SPI port.

[page] The auto-sensing bidirectional logic level converter for open-drain applications (such as I2C) also contains three states: when the EN pin is high and the NMOS is turned on, it is in the working state, and the input I/O level is pulled down to ground, that is, the input low level; when the EN pin is high and the NMOS is in high impedance state, it is in the working state, and the output I/O level is pulled up to VCC, that is, the input high level; when the EN pin is low, the converter is in the standby state. Typical auto-sensing bidirectional logic level converters for open-drain applications (such as I2C) include ON Semiconductor's NLSX4373MUTAG, NLSX4348FCT1G and NSLX4378BFCT1G. Common applications of this type of converter include I2C bus, Subscriber Identity Module (SIM) card, Single Wire (1-Wire) bus, display module, Secure Digital Input Output (SDIO) card, etc.

Of the above dual-supply logic level converters, auto-sensing converters without direction control pins and converters with direction control pins each have their own advantages and disadvantages. The advantage of auto-sensing converters is that they minimize the I/O lines of the microcontroller and are a simple solution for asynchronous communication. The disadvantage is that they are more expensive and have lower bandwidth than converters with direction control pins. The advantage of converters with direction control pins is that they are commodity components, low cost, and a simple solution for memory-mapped I/O. The disadvantage is that the number of microcontroller pins is large.

Among auto-sensing converters without a direction control pin, there is also a distinction between integrated solutions (such as the NLSX3373) and discrete solutions (such as the NTZD3154N). The integrated solution NLSX3373 is a single IC, and it is estimated that the printed circuit board (PCB) space occupied is only 2.6 mm2; the discrete solution NTZD3154N uses dual MOSFETs and four 01005 package (i.e. 0402) resistors, and the total PCB space occupied is estimated to be 3.3 mm2. The integrated solution provides a low-power standby mode, while the discrete solution does not provide a high impedance/standby mode. The low-voltage operating characteristics, bandwidth, and circuit characteristics of these two different solutions are also different.

4 ON Semiconductor Dual Supply Level Shifter Specifications and Requirements

ON Semiconductor's dual-supply logic level translators offer several advantages over competing devices. These advantages include: wider voltage conversion range, lower static power consumption, and/or support for higher data rates. For example, the dual-supply conversion range of ON Semiconductor's NLSX3013 auto-sensing bidirectional translator with push-pull output is 1.3 V to 4.5 V and 0.9 V to VCC – 0.4 V, respectively, while competing devices with similar performance have a range of 1.65 V to 3.6 V and 1.2 V to VCC – 0.4 V, respectively; both support data rates of 140 Mbps and 100 Mbps, respectively. See Table 2 for a more detailed comparison.

Table 2. Specification comparison of ON Semiconductor dual-supply logic level translator and competing devices.

An auto-sensing bidirectional converter with a push-pull output, such as the NLSX4014, has its input drive current requirements. Assuming the I/O supply voltage VL (point A) = 0 V and is to be positively converted to 2.8 V (i.e., from a low level to a high level), initially point A = point B = 0 V, IIN1 flows into the CMOS device, so IIN » IIN2, and the peak current IIN » 2.8 V/1 kΩ = 2.8 mA. This converter is designed to drive CMOS inputs and should not be used with resistive pull-up or pull-down loads with a resistance value less than 50 kΩ (see Figure 3). In addition, a push-pull type auto-sensing bidirectional converter should not be used with large capacitive loads, otherwise the output distortion will be large, and a switch type level converter should be used.

Figure 3 Automatic sensing of push-pull converter input drive current requirements

In addition, these dual-supply level converters are available in small and robust packages such as ULLGA6, UDFN6, UDFN8, UQFN12, UDFN20, uBump11, uBump12, and uBump20. The UDFN6 package measures only 1.2 mm × 1.0 mm, and the uBump12 package measures only 1.54 mm × 2.02 mm. These small and robust packages are ideal for portable applications such as smartphones.

[page]5 ON Semiconductor's complete range of logic level converters

ON Semiconductor has launched a complete series of excellent logic level conversion solutions, such as dual power converters, MiniGateTM series switches with OVT, MiniGateTM bus switches, etc. Among them, the dual power supply voltage logic level converter supports a wide range of high-to-low and low-to-high level conversion, and supports unidirectional and bidirectional signal flow, low power consumption, and ultra-small packages. MiniGateTM with OVT is used to meet the application requirements of a wide range of high-to-low level conversion and unidirectional signal flow. It is a standard component, using standard and ultra-small packages, and low cost. In addition, ON Semiconductor's MiniGateTM bus switch will be launched soon to meet the application requirements of high-speed (bandwidth above 500 MHz) and high-to-low level conversion, support bidirectional signal flow and unidirectional conversion, use standard and ultra-small packages, and low cost. These devices are used to meet the different needs of customers. Figure 4 shows the application of different logic level conversion solutions of ON Semiconductor in mobile phones.

Figure 4 Schematic diagram of ON Semiconductor's logic level conversion solution in mobile phones

6 Summary:

As a global leading supplier of high-performance, energy-efficient silicon solutions, ON Semiconductor has launched a complete series of logic level converters for portable applications such as smartphones, including various dual-supply voltage logic level converters, MiniGateTM series switches with overvoltage tolerance, and MiniGateTM bus switches for high-speed applications. Taking dual-supply voltage logic level conversion as an example, these devices provide better specifications than competing devices, such as a wider conversion voltage range, lower static power consumption, and support for higher data rates. In addition to providing first-class performance, these logic conversion devices also provide different configurations and bit widths, and use small and rugged packages, which are very suitable for various logic level conversion needs in portable applications. ■