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Analogic Tech Announces New Regulated Charge Pump

MicroPower Device Serves Emerging Portable Applications

The manufacturer says . . . ChipCenter's Paul O'Shea says . . .

Advanced Analogic Technologies, Inc., (AnalogicTech), a developer of innovative power management solutions, has added a new regulated charge pump to its growing Total Power Management IC product family. Designed for a variety of portable battery-powered applications, the AAT3110, the first of a new family, reduces board space while delivering a highly regulated output.
The AAT3110 is a MicroPower switched-capacitor voltage converter that delivers a regulated +/- 4% output. The compact device operates in an output-regulated voltage-doubling mode and uses a pulse-skipping technique to provide a regulated output from a varying input supply. No external inductor is required for operation.
"The AAT3110 charge pump can help designers of cellular phones, portable communications devices, PDAs and other handheld electronics meet new performance requirements while minimizing size and maximizing battery life," says Jan Nilsson, vice president of marketing at AnalogicTech. "As an example this device is particularly appropriate for the growing number of handheld portable devices which are integrating white light-emitting diodes (LEDs) for backlighting to support the migration to color displays and enhanced graphics capability."
To support battery-powered applications, the device combines a very low quiescent current and high efficiency over a large portion of its load range. The step-up type voltage operates over a 2.7V to 5V input range. The device delivers up to 100 mA.
By operating at a relatively high 750 kHz frequency, the AAT3110 can offer a smaller footprint than competitive devices. The compact device is available in a surface mount 6-pin SOT23 or 8-pin SC70JW package. Its compact size and elimination of external components make the AAT3110 ideal for space-constrained, portable applications.
Power consumption is a meager 13 micro amps. In shutdown mode the device draws less than 1 micro amp. A thermal management circuit protects the device under continuous short circuit conditions.
Advanced Analogic Technologies, Tel: 408-737-4654.
Analogic Tech

Charge pumps have become very popular with the emergence of hand-held, battery operated devices such as MP3 players that need a 5 V source from two double-A or triple-A batteries. The charge pump can also be used for hand-held medical instruments, like a blood sensor for diabetics, that runs on a couple battery cells but runs off 5 V.
The Analogic Tech AAT3110 is a general purpose charge pump, voltage doubler that could be used in any application needing to transform a voltage from a 2.7 V to 5 V input range to the required voltage and regulate it within +/- 4%. Another market this charge pump can be used for, which has emerged just over the past year or so, is backlighting for white LEDs. This market has grown dramatically and many charge pump manufacturers are scrambling to make dedicated white LED drivers. This AAT3110 fits the bill for driving the white LEDs but very soon you should see a dedicated charge pump for driving white LEDs from the company.
Compared to older generation charge pumps that have slower frequencies and require larger external capacitors, the AAT3110 has a higher frequency. The higher frequency allows the company to deliver an equal amount of current with a smaller capacitor or higher amount of current with the same size capacitor.
The company is making the charge pump in a CMOS process and that allows them to have very low on resistance for the internal switch capacitors. That feature differentiates this device from many other devices in the market. Inside there are switches turning on and off at 750 kHz. The low on resistance architecture is efficient and dissipates little power or heat, which enables it to deliver 100 mA in a very small package. If more resistive switches were used the package would get much hotter while delivering more current.
There are many ways to regulate the voltage on the output but this device uses a technique that doubles the voltage. So whatever you put into it you will get it doubled. Therefore, if you put 3 V in you will get 6 V out. Unfortunately, portable devices don�t use 6 V they need a regulated 5 V.
There are two ways to get 5 V - you can use a linear regulator that would burn the power and the 1 V excess is shed in the form of heat or another way (used by Analogic Tech) would be to sense the voltage on the output with an internal reference (it�s calibrated so you know where 5 V is). The former method uses a DC to DC boost converter that requires an inductor and a Schottky diode. Inductors for many portable applications aren�t desirable because they are expensive, large, and create noise and heat. In a cell phone, noise is everything for an RF circuit. An inductive DC-DC boost converter has much higher ripple, which is switching noise. It can go back out of the input device and pollute the power source on the phone, which will degrade the RF performance of the phone.
When you use DC-DC boost converters to run white LEDs, the LEDs must be connected in series so there is also a very high voltage. The boost converters in the cell phones have outputs of 14 V up to 21 V, which is a very high voltage compared to the rest of the circuit in the phone, and that propagates a lot of noise. A charge pump, however, operates at a low voltage and has low ripple. Inductors also cause problems because of their height profile. They are bulky and large and can exceed the height requirements for the components on the cell phone PCBs. This capacitive boost converter allows you to use 0805 size ceramic capacitors, which is well within the height limitations.
The charge pump uses a technique called pulse skipping to get the 5 V output required by the portable device. Here�s how it works: when the output current load is light the capacitor compensates by skipping pulses on the switching. So the output capacitor doesn�t charge when the circuit doesn�t need to draw power and it skips a pulse to compensate for a light load. Under a heavy load condition the voltages will sag so it speeds up the switching to compensate and delivers the power in a regulated fashion.
You would think that this design requires a sensor circuit and you would be right. There is a set of switches that make up the charge pump and a reference block that has an internally calibrated reference. There also is a divider on the output represented by some resistors, which are the sense resistors that sense the voltage on the output. The output voltage is then sent back to a switching control in the control block.
The external components needed to complete the circuit for the charge pump typically include three external ceramic capacitors. You can use 10 micro Farad capacitors but many designers are using 2.2 micro Farad caps. The smaller cap has more ripple noise but the noise is still low enough to be acceptable for performance in a phone. The 2.2 uF cap gets you into the 0603 size capacitor package. So it�s a tradeoff of noise for smaller size.
Finally, a thermal management circuit protects the device under continuous short circuit conditions. According to the company you could hang a paper clip on the output of the part and it wouldn�t burn it up. Under a short-circuit condition, if the output circuit for this device fails and creates a short circuit it would get very hot because too much current would be pulled through the device. The control block has a thermal sensor built-in, so when the temperature of the die gets to a certain temperature it shuts the whole circuit down. A small analog circuit that feeds into the logic of the control block constantly monitors the ambient temperature of the die. If it exceeds a certain temperature the whole part shuts down. When the part cools down enough the control block circuit allows it to turn on.
Available now in surface mount 6-pin SOT23 and 8-pin SC70JW packages, the AAT3110 is priced at $1.22 for OEM quantities of 1,000-units per month.
Data Sheet

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