数据搜索系统,热门电子元器件搜索 |
|
LM138 数据表(PDF) 6 Page - Linear Technology |
|
LM138 数据表(HTML) 6 Page - Linear Technology |
6 / 14 page LT138A/LT339A LM138/LM338 6 138afd For more information www.linear.com/LT138A Typical perForMance characTerisTics Line Transient Response Load Transient Response applicaTions inForMaTion General The LT138A develops a 1.25V reference voltage between the output and the adjustable terminal (see Figure 1). By placing a resistor, R1, between these two terminals, a constant current is caused to flow through R1 and down through R2 to set the overall output voltage. Normally this current is the specified minimum load current of 5mA or 10mA. Because IADJ is very small and constant when comparedwiththecurrentthroughR1,itrepresentsasmall error and can usually be ignored. It is easily seen from the output voltage equation, that even if the resistors were of exact value, the accuracy of the output is limited by the ac- curacyofVREF.Earlieradjustableregulatorshadareference tolerance of ± 4% which is dangerously close to the ±5% supply tolerance required in many logic and analog systems. Further, even 1% resistors can drift 0.01%/°C, adding additional error to the output voltage tolerance. For example, using 2% resistors and ±4% tolerance for VREF, calculations will show that the expected range of a 5V regulator design would be 4.66V ≤ VOUT ≤ 5.36V or approximately ±7%. If the same example were used for a 15V regulator, the expected tolerance would be ±8%. With these results most applications required some method of trimming,usuallyatrimpot.Thissolutionisbothexpensive and not conductive to volume production. One of the enhancements of Linear Technology’s adjust- able regulators over existing devices is the tightened initial tolerance of VREF . This allows relatively inexpensive 1% or 2% film resistors to be used for R1 and R2 to set the output voltage within an acceptable tolerance. With a guaranteed 1% reference, a 5V power supply design, using ±2% resistors, would have a worst-case manufacturing tolerance of ±4%. If 1% resistors are used, the tolerance will drop to ±2.5%. A plot of the worst-case output voltage tolerance as a function of resistor tolerance is shown on the front page of this data sheet. For convenience, a table of standard 1% resistor values is shown in Table 1. TIME (μs) 0 0 0.5 –1.5 –1.0 –0.5 20 30 1.5 138A/338A G13 1.0 10 40 0 0.5 1.0 CL = 1μF CL = 10μF COUT = 0 CADJ = 0 VOUT = 10V IOUT = 50mA TJ = 25°C TIME (μs) 0 2 6 –3 –2 3 0 20 40 138A/338A G14 4 1 2 –1 0 10 30 VIN = 15V VOUT = 10V TCASE = 25°C PRELOAD = 100mA CL = 1μF CADJ = 10μF CL = 0 CADJ = 0 Figure 1. Basic Adjustable Regulator LT338A VIN R1 138A/338A F01 VOUT IADJ 50μA ADJ VREF VOUT VIN R2 VOUT = VREF R2 R1 1 + + IADJ • R2 ( ) + |
类似零件编号 - LM138_15 |
|
类似说明 - LM138_15 |
|
|
链接网址 |
隐私政策 |
ALLDATASHEETCN.COM |
ALLDATASHEET是否为您带来帮助? [ DONATE ] |
关于 Alldatasheet | 广告服务 | 联系我们 | 隐私政策 | 链接交换 | 制造商名单 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 |