Datasheet LTM8071 (Analog Devices) - 16

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APPLICATIONS INFORMATION
vary from 1MHz to 1.2MHz at a 3kHz rate. When spread cause damage. Carefully evaluate whether the negative spectrum operation is selected, Burst Mode operation is buck configuration is suitable for the application. disabled, and the part will run in pulse-skipping mode. VIN The LTM8071 does not operate in forced continuous mode regardless of SYNC signal. VIN VOUT
Negative Output
LTM8071 The LTM8071 is capable of generating a negative output GND FAST LOAD voltage by connected its V TRANSIENT OUT to system GND and the LTM8071 GND to the negative voltage rail. An example OUTPUT TRANSIENT of this is shown in the Typical Applications section. The RESPONSE 8071 F01b most versatile way to generate a negative output is to
Figure 1b. Any Output Voltage Transient Appears on
use a dedicated regulator that was designed to generate
LTM8071 GND
a negative voltage, but using a buck regulator like the LTM8071 to generate a negative voltage is a simple and The CIN and COUT capacitors in Figure 1c form an AC cost effective solution, as long as certain restrictions are divider at the negative output voltage node. If VIN is hot- kept in mind. plugged or rises quickly, the resultant VOUT will be a posi- tive transient, which may be unhealthy for the application Figure 1a shows a typical negative output voltage applica- load. An antiparallel Schottky diode may be able to prevent tion. Note that LTM8071 VOUT is tied to system GND and this positive transient from damaging the load. The loca- input power is applied from VIN to LTM8071 VOUT. As a tion of this Schottky diode is important. For example, in result, the LTM8071 is not behaving as a true buck regu- a system where the LTM8071 is far away from the load, lator, and the maximum output current is depends upon placing the Schottky diode closest to the most sensitive the input voltage. In the example shown in the Typical load component may be the best design choice. Carefully Applications section, there is an attending graph that evaluate whether the negative buck configuration is suit- shows how much current the LTM8071 deliver for given able for the application. input voltages. FAST VIN TRANSIENT V V IN IN OUTPUT EXPERIENCES A POSITIVE TRANSIENT V VIN V IN VOUT OUT LTM8071 LTM8071 CIN COUT GND GND NEGATIVE OUTPUT VOLTAGE AC DIVIDER OPTIONAL 8071 F01a SCHOTTKY DIODE
Figure 1a. The LTM8071 Can Be Used to Generate a
8071 F01c
Negative Voltage Figure 1c. A Schottky Diode Can Limit the Transient
Note that this configuration requires that any load current
Caused by a Fast Rising VIN to Safe Levels
transient will directly impress the transient voltage onto If the LTM8071 is configured to provide a negative output, the LTM8071 GND, as shown in Figure 1b, so fast load do not connect BIAS to V transients can disrupt the LTM8071’s operation or even OUT or AUX. Instead, tie to BIAS to the LTM8071 GND, which should be the negative output. Rev 0 16 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Package Photos Package Description Typical Application Related Parts