LM4041AIM3 データシートの表示（PDF） - Micrel

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LM4041AIM3

Precision Micropower Shunt Voltage Reference

Micrel 

LM4040/4041

Applications Information

The LM4040 and LM4041 have been designed for stable

operation without the need of an external capacitor con-

nected between the (+) and (–) pins. If a bypass capacitor is

used, the references remain stable.

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 1. 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). Since 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)

Micrel

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 equation

(1)

VO = VREF´ [ (R2/R1) + 1 ]

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

(2)

VREF´ = VO (∆VREF / ∆VO) + VY

where VO is the desired output voltage. ∆VREF / ∆VO is found

in the Electrical Characteristics and is typically –1.3mV/V and

VY is equal to 1.233V. Replace the value of VREF´ in equation

(1) with the value found using equation (2).

Note that actual output voltage can deviate from that pre-

dicted using the typical ∆VREF / ∆VO in equation (2); for C-

grade parts, the worst-case ∆VREF / ∆VO 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

∆VREF / ∆VO:

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

is 1.223V. Choosing a value of R1 = 10kΩ, R2 = 63.272kΩ.

Using the worst case ∆VREF / ∆VO 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

∆VREF / ∆VO will work in most cases, requiring no further

adjustment.

+

FB

R1

120k

LM4041-ADJ

D1

–

R2

1M

λ

R3

200

< –12V

LED ON

–5V

Figure 3. Voltage Level Detector

λ

D1

+

FB

LM4041-

ADJ –

R1

120k

R2

1M

> –12V

R3

330

LED ON

–5V

Figure 4. Voltage Level Detector

LM4040/4041

12

January 2000

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