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LTM8073

8073fa

For more information www.linear.com/LTM8073

Figure 1a. The LTM8073 Can Be Used to Generate a

Negative Voltage

applicaTions inForMaTion

Negative Output

The LTM8073 is capable of generating a negative output

voltage by connected its VOUT to system GND and the

LTM8073 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

LTM8073 to generate a negative voltage is a simple and

cost effective solution, as long as certain restrictions are

kept in mind.

Figure 1a shows a typical negative output voltage applica-

tion. Note that LTM8073 VOUT is tied to system GND and

input power is applied from VIN to LTM8073 VOUT. As a

result, the LTM8073 is not behaving as a true buck regu-

lator, and the maximum output current is depends upon

the input voltage. In the example shown in the Typical

Applications section, there is an attending graph that

shows how much current the LTM8073 deliver for given

input voltages.

The CIN and COUT capacitors in figure 1c form an AC

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

plugged or rises quickly, the resultant VOUT will be a posi-

tive transient, which may be unhealthy for the application

load. An antiparallel Schottky diode may be able to pre-

vent this positive transient from damaging the load. The

location of this Schottky diode is important. For example,

in a system where the LTM8073 is far away from the load,

placing the Schottky diode closest to the most sensitive

load component may be the best design choice. Carefully

evaluate whether the negative buck configuration is suit-

able for the application.

Note that this configuration requires that any load current

transient will directly impress the transient voltage onto

the LTM8073 GND, as shown in Figure 1b, so fast load

transients can disrupt the LTM8073’s operation or even

cause damage. Carefully evaluate whether the negative

buck configuration is suitable for the application.

NEGATIVE

OUTPUT VOLTAGE

LTM8073

VOUT

VIN

8073 F01a

GND

VIN

FAST LOAD

TRANSIENT

OUTPUT

TRANSIENT

RESPONSE

LTM8073

VOUT

VIN

8073 F01b

GND

VIN

FAST VIN

TRANSIENT

OUTPUT EXPERIENCES

A POSITIVE TRANSIENT

LTM8073

VOUT

VIN

8073 F01c

GND

COUT

CIN

OPTIONAL

SCHOTTKY

DIODE

AC DIVIDER

VIN

Figure 1b. Any Output Voltage Transient Appears on

LTM8073 GND

Figure 1c. A Schottky Diode Can Limit the Transient

Caused by a Fast Rising VIN to Safe Levels

If the LTM8073 is configured to provide a negative output,

do not connect BIAS to VOUT or AUX. Instead, tie to BIAS to

the LTM8073 GND, which should be the negative output.

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