LTM8021 datasheet(19/28 Pages) LINER

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LTM8053

8053fc

For more information www.linear.com/LTM8053

Figure 1a. The LTM8053 Can Be Used to Generate a

Negative Voltage

APPLICATIONS INFORMATION

Negative Output

The LTM8053 is capable of generating a negative output

voltage by connected its VOUT to system GND and the

LTM8053 GND to the negative voltage rail. An example

of this is shown in the Typical Applications section. The

most versatile way to generate a negative output is to

use a dedicated regulator that was designed to generate

a negative voltage, but using a buck regulator like the

LTM8053 to generate a negative voltage is a simple and

cost effective solution, as long as certain restrictions are

kept in mind.

Note that this configuration requires that any load current

transient will directly impress the transient voltage onto

the LTM8053 GND, as shown in Figure 1b, so fast load

transients can disrupt the LTM8053’s operation or even

cause damage. Carefully evaluate whether the negative

buck configuration is suitable for the application.

Figure 1a shows a typical negative output voltage appli-

cation. Note that LTM8053 VOUT is tied to system GND

and input power is applied from VIN to LTM8053 VOUT.

As a result, the LTM8053 is not behaving as a true buck

regulator, and the maximum output current is depends

upon the input voltage. In the example shown in the Typi-

cal Applications section, there is an attending graph that

shows how much current the LTM8053 deliver for given

input voltages.

NEGATIVE

OUTPUT VOLTAGE

LTM8053

VOUT

VIN

8053 F01a

GND

VIN

FAST LOAD

TRANSIENT

OUTPUT

TRANSIENT

RESPONSE

LTM8053

VOUT

VIN

8053 F01b

GND

VIN

FAST VIN

TRANSIENT

OUTPUT EXPERIENCES

A POSITIVE TRANSIENT

LTM8053

VOUT

VIN

8053 F01c

GND

COUT

CIN

OPTIONAL

SCHOTTKY

DIODE

AC DIVIDER

VIN

Figure 1b. Any Output Voltage Transient Appears on

LTM8053 GND

Figure 1c. A Schottky Diode Can Limit the Transient

Caused by a Fast Rising VIN to Safe Levels

TheCINandCOUTcapacitorsinfigure1cformanACdivider

at the negative output voltage node. If VIN is hot-plugged

or rises quickly, the resultant VOUT will be a positive tran-

sient, which may be unhealthy for the application load.

An antiparallel Schottky diode may be able to prevent

this positive transient from damaging the load. The loca-

tion of this Schottky diode is important. For example, in

a system where the LTM8053 is far away from the load,

placing the Schottky diode closest to the most sensitive

load component may be the best design choice. Carefully

evaluatewhetherthenegativebuckconfigurationissuitable

for the application. When generating a negative output,

connect BIAS to LTM8053 GND.

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