LM4040(2014) Просмотр технического описания (PDF) - Micrel

Номер в каталоге

Компоненты Описание

производитель

LM4040
(Rev.:2014)

Precision Micropower Shunt Voltage Reference

Micrel 

Micrel, Inc.

Applications Information

The stable operation of the LM4040 and LM4041

references requires an external capacitor greater than

10nF connected between the (+) and (–) pins. Bypass

capacitors with values between 100pF and 10nF have

been found to cause the devices to exhibit instabilities.

Schottky Diode

LM4040-x.x and LM4041-1.2 in the SOT-23 package

have a parasitic Schottky diode between pin 2 (–) and pin

3 (die attach interface connect). Pin 3 of the SOT-23

package must float or be connected to pin 2. The

LM4041-ADJs use pin 3 as the (–) output.

Conventional Shunt Regulator

In a conventional shunt regulator application (see Figure

1), an external series resistor (RS) is connected between

the supply voltage and the LM4040-x.x or LM4041-1.2

reference. RS determines the current that flows through

the load (IL) and the reference (IQ). Because load current

and supply voltage may vary, RS should be small enough

to supply at least the minimum acceptable IQ to the

reference even when the supply voltage is at its minimum

and the load current is at its maximum value. When the

supply voltage is at its maximum and IL is at its minimum,

RS should be large enough so that the current flowing

through the LM4040-x.x is less than 15mA, and the

current flowing through the LM4041-1.2 or LM4041-ADJ

is less than 12mA.

RS is determined by the supply voltage (VS), the load and

operating current, (IL and IQ), and the reference’s reverse

breakdown voltage (VR):

RS = (VS – VR) / (IL + IQ)

Eq. 1

LM4040/LM4041

Adjustable Regulator

The LM4041-ADJ’s output voltage can be adjusted to any

value in the range of 1.24V through 10V. It is a function of

the internal reference voltage (VREF) and the ratio of the

external feedback resistors as shown in Figure 2. The

output is found using the following equation:

VO = VREF [(R2/R1) + 1]

Eq. 2

where VO is the desired output voltage. The actual value

of the internal VREF is a function of VO. The corrected VREF

is determined by:

VREF = VO (ΔVREF/ΔVO) + VY

Eq. 3

where VO is the desired output voltage. ΔVREF/ΔVO is

found in the Electrical Characteristics section and is

typically –1.3mV/V and VY is equal to 1.233V. Replace

the value of VREF in Equation 2 with the value VREF found

using Equation 3.

Note that actual output voltage can deviate from that

predicted using the typical ΔVREF/ΔVO in Equation 3; for

C-grade parts, the worst-case ΔVREF/ΔVO is –2.5mV/V

and VY = 1.248V.

The following example shows the difference in output

voltage resulting from the typical and worst case values

of ΔVREF/ΔVO.

Let VO = +9V. Using the typical values of ΔVREF/ΔVO, VREF

is 1.223V. Choosing a value of R1 = 10kΩ, R2 =

63.272kΩ. Using the worst case ΔVREF/ΔVO for the C-

grade and D-grade parts, the output voltage is actually

8.965V and 8.946V respectively. This results in possible

errors as large as 0.39% for the C-grade parts and 0.59%

for the D-grade parts. Once again, resistor values found

using the typical value of ΔVREF/ΔVO will work in most

cases, requiring no further adjustment.

June 24, 2014

14

Revision 3.0

Share Link: