1 Features

96% Efficient Synchronous Boost Converter

When the input voltage exceeds the rated output voltage, the output voltage remains stable

Device Quiescent Current: 25µA (typ)

Input voltage range: 0.9 V to 6.5 V

Fixed and adjustable output voltage options up to 5.5 V

Energy saving mode for increased efficiency at low output power

low battery comparator

Low EMI converter (integrated anti-ringing switch)

Disconnect load during shutdown

Overheating protection

3-mm×3-mm VSON-10 small package

2 apps

All single-cell, dual-cell and triple-cell alkaline, NiCd or NiMH, or single cell Li-Ion or Li-Polymer

battery powered products

Portable Audio Player

PDA

cell phone

personal medical products

Camera white LED flash

Typical schematic

illustrate

The TPS6102x family of devices provide power solutions for products powered by single-cell, dual-cell, or triple-cell alkaline, NiCd or NiMH, single-cell Li-Ion, or Li-polymer batteries. When using a single-cell alkaline battery, the output current can be as high as 200mA and discharge it to 0.9V. The device can also be used to generate 5V at 500mAh from a 3.3V rail or a Li-Ion battery. The boost converter is based on a fixed frequency, pulse width modulation (PWM) controller using synchronous rectifiers for maximum efficiency. At low load currents, the converter enters a power-saving mode to maintain high efficiency over a wide load current range. Power saving mode can be disabled, forcing the converter to operate at a fixed switching frequency. The maximum peak current in the boost switch is limited to 800mA, 1500mA or 1800mA, depending on the version of the device.

The TPS6102x devices maintain output voltage regulation even when the input voltage exceeds the rated output voltage. The output voltage can be programmed via an external resistor divider or fixed inside the chip. The converter can be disabled to minimize battery drain. During shutdown, the load is completely disconnected from the battery. A low EMI mode is implemented to reduce ringing and, in fact, reduce radiated electromagnetic energy when the converter enters discontinuous conduction mode. The device is packaged in a 10-pin VSON Power Strip™ package measuring 3 mm x 3 mm (DRC).

Parameter measurement information

Overview

The TPS6102x is based on a fixed frequency, pulse width modulation (PWM) controller using synchronous rectification for maximum efficiency. The input voltage, output voltage, and voltage drop across the NMOS switch are monitored and forwarded to the regulator. Therefore, changes in the converter operating conditions directly affect the duty cycle. At low load currents, the converter enters a power saving mode to ensure high efficiency over a wide load current range. Power saving mode can be disabled, forcing the converter to operate at a fixed switching frequency.

Functional block diagram

Feature description

controller circuit

The controller circuit of the device is based on a fixed frequency multiple feedforward controller topology. The input voltage, output voltage, and voltage drop across the NMOS switch are monitored and forwarded to the regulator. Therefore, changes in the converter operating conditions directly affect the duty cycle, which cannot be taken in an indirect and slow manner through the control loop and error amplifier. The control loop determined by the error amplifier only needs to deal with small signal errors. Its input is the feedback voltage on the FB pin, or in the case of a fixed output voltage, the voltage on the internal resistor divider. By comparing with the internal reference voltage, an accurate and stable output voltage is obtained.

The peak current of the NMOS switch is also sensed to limit the maximum current flowing through the switch and inductor. An internal temperature sensor prevents the device from overheating to prevent excessive power consumption.

Synchronous Rectifier

The device integrates N-channel and P-channel MOSFET transistors for synchronous rectification. The power conversion efficiency reaches 96% due to the replacement of the commonly used discrete Schottky rectifiers with low RDS(ON) PMOS switches. To avoid ground offset due to high current in the NMOS switch, two separate ground pins are used. The reference for all control functions is the GND pin. The source of the NMOS switch is connected to PGND. Both grounds must be connected to the PCB only at one point close to the ground pins. A special circuit is used to disconnect the load from the input during drive shutdown. In a traditional synchronous rectifier circuit, the back gate diode of the high-side PMOS is forward biased when turned off, allowing current to flow from the battery to the output. However, this unit uses a special circuit that receives the cathode of the back gate diode of the high-side PMOS and disconnects it from the power supply (EN=low) when the regulator is not enabled.

The benefit of this feature to the system design engineer is that the battery does not drain while the converter is turned off. There is no need to add additional components to the design to ensure that the battery is disconnected from the converter output.

down

In general, boost converters only regulate output voltages that are higher than the input voltage. This device works differently. For example, it is capable of regulating 3.0 V on the output, using two new alkaline batteries on the input, for a total battery voltage of 3.2 V. Another example is powering a white LED with a forward voltage of 3.6 V from a fully charged Li-Ion battery (4.2 V output). To properly control these applications, a downconversion mode is implemented.

If the input voltage reaches or exceeds the output voltage, the converter will switch to conversion mode. In this mode, the control circuit changes the behavior of the rectifier PMOS. It sets the voltage drop across the PMO to the high value required to regulate the output voltage. This means increased power losses in the converter. This has to take thermal considerations into account. As soon as the input voltage drops about 50mV below the output voltage, the downconversion mode is automatically turned off. For proper operation in downconversion mode, the output voltage should not be programmed below 50% of the maximum input voltage that can be applied.

device enabled

When EN is set high, the device is put into operation. When EN is set to GND, it will enter shutdown mode. In shutdown mode, the regulator stops switching, all internal control circuits including the low-battery comparator are turned off, and the load is isolated from the input (as described in the Synchronous Rectifier section). This also means that during shutdown, the output voltage may be lower than the input voltage. During startup of the converter, the duty cycle and peak current are limited to avoid drawing high peak currents from the battery.

Characterization (continued)

undervoltage lockout

The undervoltage lockout feature prevents the device from starting up if the supply voltage on VBAT falls below about 0.8 V. During operation and battery discharge, if the voltage on VBAT falls below approximately 0.8 V, the device will automatically enter shutdown mode. This undervoltage lockout feature is implemented to prevent converter failures.

Soft-Start and Short-Circuit Protection

When the device starts up, the internal boot cycle begins with the first step, the precharge phase. During precharge, the rectifier switch is turned on until the output capacitor is charged to a value close to the input voltage. The rectifier switch is current limited during this phase. The current limit increases as the output voltage increases. The circuit also limits the output current during output short-circuit conditions. Figure 12 shows typical precharge current versus output voltage for a specific input voltage:

Precharge and Short Circuit Current

After charging the output capacitor to the input voltage, the device starts switching. If the input voltage is below 1.4V, the device operates at a fixed duty cycle of 50% until the output voltage reaches 1.4V. Then set the duty cycle according to the input to output voltage ratio. Before the output voltage reaches its nominal value, the current limit of the boost switch is set to 40% of its nominal value to avoid high battery peak currents during startup. Once the output voltage is reached, the regulator takes control and the switch current limit is set back to 100%.

Low battery detection circuit LBI/LBO

A low battery detection circuit is typically used to monitor the battery voltage and generate an error flag when the battery voltage falls below a user-set threshold voltage. This feature is only activated when the device is enabled. When the device is disabled, the LBO pin is high impedance. The switching threshold at LBI is 500 mV. During normal operation, when the voltage applied at the LBI is above the threshold, the LBO remains at high impedance. When the voltage of LBI is lower than 500 mV, it is in the low active state.

The battery voltage when the detection circuit switches, is programmable through a resistor divider connected to the LBI pin. A resistor divider reduces the battery voltage to a voltage level of 500 mV, which is then compared to the LBI threshold voltage. The LBI pin has a built-in hysteresis of 10 mV. See the Applications section for more details on LBI threshold programming. If the low battery detection circuit is not used, the LBI pin should be connected to GND (or VBAT), while the LBO pin can be left unconnected. Do not let the LBI pin float.

Characterization (continued)

Low EMI switch

The device integrates a circuit that cancels the ringing that normally occurs at the SW node when the converter enters discontinuous current mode. In this case, the current through the inductor becomes zero and the rectifying PMOS switch is turned off to prevent reverse current from flowing back to the battery from the output capacitor. Ringing occurs on the SW pin due to residual energy stored in parasitic elements of semiconductors and inductors. An integrated anti-vibration switch clamps this voltage to VBAT, suppressing ringing.

Device functional mode

undervoltage lockout

The undervoltage lockout feature prevents the device from starting up if the supply voltage on VBAT falls below about 0.8 V. During operation and battery discharge, if the voltage on VBAT falls below approximately 0.8 V, the device will automatically enter shutdown mode. This undervoltage lockout feature is implemented to prevent converter failures.

power saving mode

The PS pin can be used to select different modes of operation. To enable power saving, PS must be set to low. To improve efficiency at light loads, a power saving mode is employed. In power saving mode, the converter will only operate when the output voltage jumps below the set threshold voltage. It increases the output voltage with one or more pulses, and once the output voltage exceeds a set threshold voltage, it enters power-saving mode again. This power saving mode can be disabled by setting PS to VBAT. In downconversion mode, the power saving mode is always active and the device cannot be forced into fixed frequency operation at light loads.

programming

Output voltage programming

The output voltage of the TPS61020 DC-DC converter can be adjusted by an external resistor divider. The typical voltage value at the FB pin is 500 mV. The maximum recommended value for the output voltage is 5.5 V. The current through the resistor divider should be about 100 times larger than the current going into the FB pin. The typical current at the FB pin is 0.01µA and the voltage on R4 is typically 500mV. Based on these two values, the recommended value for R4 should be below 500 kΩ in order to set the voltage divider current to 1 µA or higher. Due to the internal compensation circuit, the value of this resistor should be in the range of 200 kΩ. Thus, the value of resistor R3, depending on the desired output voltage (VO), can be calculated using Equation 1:

For example, if an output voltage of 3.3 V is required, a 1.0 MΩ resistor should be chosen for R3. If, for any reason, the value of R4 is chosen significantly lower than 200 kΩ, additional capacitors in parallel with R3 are recommended in case the device shows unstable output voltage regulation. The required capacitance value can be easily calculated using Equation 2

Program LBI/LBO Threshold Voltage

The current through the resistor divider should be about 100 times larger than the current going into the LBI pin. The typical current into the LBI pin is 0.01µA, and the voltage across R2 is equal to the LBI voltage threshold generated on the chip, which has a value of 500mV. Therefore, the recommended value of R2 is in the range of 500 kΩ. Thus, the value of resistor R1, depending on the required minimum battery voltage VBAT, can be calculated using Equation 3.

Programming (continued)

The output of the low-battery battery manager is a simple open-drain output that becomes active low if the dedicated battery voltage falls below the programmed threshold voltage on the LBI. The output requires a pull-up resistor with a recommended value of 1 MΩ. If not used, the LBO pin can be left floating or tied to GND.

Application and Implementation

Notice

The information in the application section below is not part of the TI component specification and TI does not warrant its accuracy or completeness. TI's customers are responsible for determining the suitability of parts for their purpose. Customers should verify and test their design implementation to confirm system functionality.

Application Information

These devices are designed to operate over an input voltage supply range between 0.9 V (1.2 V for VIN rising UVLO) and 6.5 V, with a maximum switch current limit of 1.8 A. These devices operate in PWM mode under moderate to heavy load conditions and in power saving mode at light load currents. In PWM mode, the TPS6102x converters typically operate at a nominal switching frequency of 600 kHz. As the load current decreases, the converter enters a power-saving mode, reducing the switching frequency, reducing the IC quiescent current, and achieving high efficiency over the entire load current range. Connecting the PS pin to a logic high level disables the power saving mode, forcing the converter to operate at a fixed switching frequency.

typical application

Typical application of the TPS6102x with a 1.2-V to 6.5-V input range and 800 mA output current.

Design requirements

The TPS6102x DC-DC converters are suitable for systems powered by single-cell to triple-cell alkaline, NiCd, and NiMH batteries with typical termination voltages between 0.9 V and 6.5 V. They can also be used in systems powered by single-cell Li-Ion or Li-Polymer with typical voltages between 2.5 V and 4.2 V. Additionally, any other voltage source with a typical output voltage between 0.9 V and 6.5 V can power a system using the TPS6102x.

Detailed design procedure

Sensor selection

A boost converter typically requires two main passive components to store energy. A boost inductor and a storage capacitor are required at the output. To select the boost inductor, it is recommended to keep the possible inductor peak current below the current limit threshold of the power switch in the selected configuration. For example, at an output voltage of 5v, the current limit threshold of the TPS61029 switch is 1800ma. The maximum peak current through the inductor and switch depends on the output load, input (VBAT) and output voltage (VOUT). The maximum average inductor current can be estimated using Equation 4:

Power Recommendations

This input supply should be well regulated with the TPS6102x ratings. If the input power supply is more than a few inches away from the device, additional bulk capacitors may be required in addition to ceramic bypass capacitors. A typical choice is to use an electrolytic or tantalum capacitor with a value of 47µF.

Layout Guidelines

As with all switching power supplies, layout is an important step in the design, especially at high peak currents and high switching frequencies. If the layout is not careful, the regulator can have stability problems and electromagnetic interference problems. Therefore, wide and short traces should be used for the main current paths and power ground traces. The power supply grounding adopts the same grounding node, and the control grounding adopts different grounding nodes to reduce the influence of ground noise. Connect these ground nodes anywhere close to one of the IC's ground pins. The most critical current path for any boost converter is from the switching FET, through the synchronous FET, then the output capacitor, and back to the ground of the switching FET. Therefore, both output capacitors and their traces should be placed on the same board layer, as close as possible to the VOUT and PGND pins of the IC. Especially at output voltages above 4.5v, adding an RC snubber from the SW pin to the PGND pin may help further reduce the parasitic inductance effects of this critical current path. See the application report (SLVA255) for details on implementing buffering. Also, the input capacitors should be placed as close as possible between the VBAT and PGND pins of the IC. Placing the inductor close to the switch pins helps improve efficiency and minimize EMI. In order to route the control ground, it is recommended to also use a short circuit separate from the power ground. This avoids ground offset issues due to the superposition of power supply ground currents and control ground currents.

Thermal factor

Implementing integrated circuits in low-profile and fine-pitch surface mount packages often requires special attention to power dissipation. Many system-related issues, such as thermal coupling, airflow, added heat sinks and convective surfaces, and the presence of other heat-generating components, can affect the power consumption limit of a given component.

Three basic ways to improve thermal performance are listed below.

Improve the power dissipation capability of PCB design

Improve thermal coupling of components to the PCB

Introduce airflow into the system

The maximum recommended junction temperature (TJ) for the TPS6102x devices is 125°C. If the power board is soldered, the thermal resistance of the 10-pin VSON 3×3 package (DRC) is RΘ=47.2°C/W. The specified regulator operation ensures a maximum ambient temperature TA of 85°C. Therefore, the maximum power consumption is about 847 MW. If the maximum ambient temperature of the application is lower, more power can be dissipated. Youth Achievement Organization

TJ (max)-TA 125°-C 85°C

PD (max) === 847 MW

RqJA 47.2 degrees Celsius/Watt (8)