BM1117-ADJ 查看數據表（PDF） - Unspecified

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BM1117-ADJ

Voltage Regulators

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SPECIFICATION

.current paths on the BM1117 adjustment

pin, therefore even with capacitors on the

adjustment pin no protection diode is

needed to ensure device safety under

short-circuit conditions.

Diodes between the input and output are

not usually needed. Microsecond surge

currents of 50A to 100A can be handled by

the internal diode between the input and

output pins of the device. In normal

operations it is difficult to get those values

of surge currents even with the use of

large output capacitances. If high value

output capacitors are used, such as

1000mF to 5000mF and the input pin is

instantaneously shorted to ground,

BM1117

damage can occur. A diode from output to

input is recommended, when a crowbar

circuit at the input of the BM1117 is used

(Figure 1).

Output Voltage

The BM1117 series develops a 1.25V

reference voltage between the output and

the adjust terminal. Placing a resistor

between these two terminals causes a

constant current to flow through R1 and

down through R2 to set the overall output

voltage. This current is normally the

specified minimum load current of 10mA.

Because IADJ is very small and constant it

represents a small error and it can usually

be ignored

BM1117

VIN

IN

OUT

VOUT

ADJ

R1

COUT

22uF

CADJ

R2

10uF

BM1117

VIN

IN

OUT

VOUT

ADJ

VREF

R1

IADJ

50uA

R2

Figure 1.

VOUT = VRE F (1+ R2/R1)+IADJR2

Figure 2. Basic Adjustable Regulator

Load Regulation

True remote load sensing it is not possible

to provide, because the BM1117 is a three

terminal device. The resistance of the wire

effective resistance between the regulator

and the load would be:

RP x ((R2+R1)/ R1),

RP = Parasitic Line Resistance

connecting the regulator to the load will

limit the load regulation. The data sheet

specification for load regulation is

measured at the bottom of the package.

BM1117

VIN IN

OUT

ADJ

Rp

R1*

RL

Negative side sensing is a true Kelvin

R2*

connection, with the bottom of the output

divider returned to the negative side of the

load.

The best load regulation is obtained when

the top of the resistor divider R1 is

connected directly to the case not to the

load. If R1 were connected to the load, the

*CONNECT R1 TO CASE

*CONNECT R2 TO LOAD

Figure 3. Connections for Best

Load Regulation

BOOKLY MICRO ELECTRONICS LIMITED CORP.

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