![]() |
Electronic Components Datasheet Search |
|
REF192 Datasheet(PDF) 20 Page - Analog Devices |
|
|
REF192 Datasheet(HTML) 20 Page - Analog Devices |
20 / 24 page ![]() REV. E –20– REF19x Series 1 F REF19x VIN GND VREF SLEEP VIN ISY ADJUST R1 P1 RL RSET IOUT VIN IOUT RL (MAX) + VSY (MIN) IOUT = + ISY (REF19x) RSET VOUT RSET VOUT >> ISY E.G. REF195 : VOUT = 5V IOUT = 5mA R1 = 953 P1 = 100 , 10-TURN Figure 8. A Low Dropout, Precision Current Source The circuit’s governing equations are: V IN = I OUT × R L(max ) +V SY (min, REF19x ) IOUT = VOUT RSET + I SY ( REF19x ) VOUT RSET 〉〉I SY ( REF19x ) Switched Output 5 V/3.3 V Reference Applications often require digital control of reference voltages, selecting between one stable voltage and a second. With the sleep feature inherent to the REF19x series, switched output reference configurations are easily implemented with relatively little additional hardware. The circuit of Figure 9 illustrates the general technique, which takes advantage of the output “wire-OR” capability of the REF19x device family. When OFF, a REF19x device is effectively an open circuit at the output node with respect to the power supply. When ON, a REF19x device can source current up to its current rating, but sink only a few µA (essentially just the relatively low current of the internal output scaling divider). As a result, for two devices wired together at their common outputs, the output voltage is simply that of the ON device. The OFF state device will draw a small standby current of 15 µA (max), but otherwise will not interfere with operation of the ON device, which can operate to its full current rating. Note that the two devices in the circuit conveniently share both input and output capacitors, and with CMOS logic drive, it is power efficient. U1 REF19x (SEE TABLE) C1 0.1 F +VS = 6V VIN COMMON VOUT COMMON +VOUT C2 1 F U2 REF19x (SEE TABLE) 3 4 1 2 U3B 74HC04 U3A 74HC04 VC OUTPUT TABLE VOUT (V) 5.0 3.3 4.5 5.0 VC* HI LO HI LO U1/U2 REF195/ REF196 REF194/ REF195 *CMOS LOGIC LEVELS Figure 9. Switched Output Reference Using dissimilar REF19x series devices with this configuration allows logic selection between the U1/U2 specified terminal voltages. For example, with U1 (a REF195) and U2 (a REF196), as noted in the table, changing the CMOS compatible VC logic control voltage from HI to LO selects between a nominal output of 5.000 V and 3.300 V and vice versa. Other REF19x family units can also be used for U1/U2, with similar operation in a logic sense, but with outputs as per the individual paired devices (see table, again). Of course, the exact output voltage tolerance, drift, and overall quality of the reference voltage will be consistent with the grade of individual U1 and U2 devices. Because of the nature of the wire–OR, there is one application caveat that should be understood about this circuit. Since U1 and U2 can only source current effectively, negative going output voltage changes, which require the sinking of current, will neces- sarily take longer than positive going changes. In practice, this means that the circuit is quite fast when undergoing a transition from 3.3 V to 5 V, but the transition from 5 V to 3.3 V will take longer. Exactly how much longer will be a function of the load resistance, RL, seen at the output and the typical 1 µF value of C2. In general, a conservative transition time here will be on the order of several milliseconds for load resistances in the range of 100 Ω to 1 kΩ. Note that for highest accuracy at the new output voltage, several time constants should be allowed (>7.6 time constants for <1/2 LSB error @ 10 bits, for example). |
Similar Part No. - REF192 |
|
Similar Description - REF192 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |