LT6660 UUWUAPPLICATIO S I FOR ATIOLonger Battery Life Series references have a large advantage over older shunt VGEN 2.5V style references. Shunt references require a resistor 1.5V from the power supply to operate. This resistor must be chosen to supply the maximum current that can ever be VOUT 1mA demanded by the circuit being regulated. When the circuit being controlled is not operating at this maximum current, VOUT 10mA the shunt reference must always sink this current, resulting in high dissipation and short battery life. 1µs/DIV 6660 F02 The LT6660 series references do not require a current setting resistor and can operate with any supply voltage Figure 2. CL = 0µF from VOUT + 0.9V to 20V. When the circuitry being regu- lated does not demand current, the LT6660s reduce their dissipation and battery life is extended. If the references are not delivering load current, they dissipate only several VGEN 2.5V mW, yet the same connection can deliver 20mA of load 1.5V current when demanded. VOUT 1mA Capacitive Loads V 10mA The LT6660 family of references are designed to be stable OUT with a large range of capacitive loads. With no capacitive load, these references are ideal for fast settling or applica- 100µs/DIV 6660 F03 tions where PC board space is a premium. The test circuit shown in Figure 1 is used to measure the response time Figure 3. CL = 0.1µF and stability of various load currents and load capacitors. This circuit is set for the 2.5V option. For other voltage options, the input voltage must be scaled up and the output voltage generator offset voltage must be adjusted. VGEN 2.5V The 1V step from 2.5V to 1.5V produces a current step of 1.5V 10mA or 1mA for RL = 100Ω or RL = 1k. Figure 2 shows the response of the reference to these 1mA and 10mA VOUT 1µF load steps with no load capacitance, and Figure 3 shows a 1mA and 10mA load step with a 0.1µF output capaci- VOUT 4.7µF tor. Figure 4 shows the response to a 1mA load step with CL = 1µF and 4.7µF. 100µs/DIV 6660 F04 Figure 4. IOUT = 1mA R V L OUT VIN = 2.5V LT6660-2.5 VGEN C 2.5V IN 0.1µF CL 1.5V 6660 F01 Figure 1. Response Time Test Circuit 6660fa 8