Introduction
ALD810029/ALD910029 are new additions to the ALD8100xx (quad-channel) and ALD9100xx (dual-channel) Supercapacitor Auto Balance MOSFET (SAB™ MOSFET) families. SAB MOSFETs are fabricated using production-proven EPAD® technology, designed to address voltage and leakage current balancing of series-connected supercapacitors. Supercapacitors, also known as ultracapacitors or supercaps, can achieve leakage current balancing in series connections and prevent overvoltage by connecting one or more devices across each supercapacitor cell.
ALD810029 provides each of its four SAB MOSFET devices with a unique, precise set of operating voltage and current characteristics. It can be used to balance up to four series-connected supercapacitors. ALD910029 provides each of its two SAB MOSFET devices with a unique set of precision operating electrical characteristics, suitable for up to two series-connected supercapacitors.
Each SAB MOSFET features a precise gate threshold voltage in Vt mode, which is 2.90V when the gate-drain-source terminals (VGS = VDS) are connected together at a drain-source current IDS(ON) = 1µA. In this mode, input voltage VIN = VGS = VDS. Different VIN levels produce output current IOUT = IDS(ON) characteristics, forming an effective variable resistance whose value varies exponentially with VIN. When this VIN is connected across each series-connected supercapacitor, it balances the voltage and current of each supercapacitor within its rated limits.
When VIN = 2.90V is applied to ALD810029/ALD910029, IOUT is 1µA. When VIN increases by 100mV to 3.00V, IOUT increases approximately 10-fold. For ALD910029, when VIN further increases to 3.12V (3.14V for ALD810029), IOUT increases 100-fold to 100µA. Conversely, when VIN decreases by 100mV to 2.80V, IOUT drops to one-tenth of its previous value, i.e., 0.1µA. A further 100mV decrease in input voltage reduces IOUT to 0.01µA. Therefore, when ALD810029/ALD910029 SAB MOSFETs are connected across a supercapacitor charged to below 2.70V, they consume essentially no power.
The voltage-dependent on-resistance characteristics of ALD810029/ALD910029 effectively control overvoltage rise across supercapacitors when connected in parallel with them. In a series-connected supercapacitor bank, when the voltage of one supercapacitor rises, the voltages of the others fall, with the supercapacitor exhibiting the highest leakage current having the lowest voltage. The SAB MOSFETs connected across these supercapacitors exhibit complementary, inverse current levels, generating virtually no additional leakage current beyond that produced by the supercapacitors themselves.
