ADP7185ACPZN-R7 datasheet(15/19 Pages) AD

15 / 19 page

Data Sheet

ADP7185

Rev. 0 | Page 15 of 19

APPLICATIONS INFORMATION

ADIsimPOWER DESIGN TOOL

The ADIsimPower™ design tool set supports the ADP7185.

ADIsimPower is a collection of tools that produce complete

power designs optimized for a specific design goal. The tools

enable the user to generate a full schematic, bill of materials,

and calculate performance in minutes. ADIsimPower can

optimize designs for cost, area, efficiency, and parts count,

taking into consideration the operating conditions and

limitations of the IC and all external components. For more

information about, and to obtain ADIsimPower design tools,

visit www.analog.com/ADIsimPower.

CAPACITOR SELECTION

Output Capacitor

The ADP7185 operates with small, space-saving ceramic

capacitors; however, it also functions with general-purpose

capacitors as long as care is taken with regard to the effective

series resistance (ESR) value. The ESR of the output capacitor

affects the stability of the LDO regulator control loop. A

minimum of 4.7 μF capacitance with an ESR of 0.05 Ω or less is

recommended to ensure the stability of the ADP7185. Output

capacitance affects the transient response to changes in load

currents. Using a larger value for the output capacitance improves

the transient response of the ADP7185 to large changes in load

current. Figure 46 shows the transient response for an output

capacitance value (COUT) of 4.7 μF.

CH1 –475mA

500mA/DIV

CH2 5.0mV

9.9mV

10.0µs/DIV

2MS 20GS/s

STOP –220mA

EDGE POSITIVE

ILOAD

VOUT

Figure 46. Output Transient Response, COUT = 4.7 μF, VOUT = −1.2 V

Input Bypass Capacitor

Connecting a 4.7 μF or greater capacitor from VIN to GND

reduces the circuit sensitivity to the PCB layout, especially when

long input traces or high source impedance are encountered.

When more than 4.7 μF of output capacitance is required,

increase the input capacitance to match it.

CA and CAFB Capacitors

The ultralow output noise of the ADP7185 is achieved by

keeping the LDO error amplifier in unity gain and setting the

reference voltage equal to the output voltage. In this architecture,

the resistor driven by the GM amplifier adjusts the reference

voltage to the selected output voltage. To ensure the GM amplifier

stability, the CA capacitor is needed to generate the dominant

pole and to keep the GM amplifier stable across all conditions.

CA also serves as a dampening capacitor to the inputs of the

LDO error amplifier for improved PSRR. However, the LDO

output noise scales by the GM amplifier amount of gain as a

function of the output voltage. To minimize the output voltage

noise contributed by the GM amplifier, the CAFB capacitor must

be connected between the VA and VAFB pins to keep the ac

gain of the GM amplifier in unity.

REFERENCE

VAFB

GND

CAFB

Figure 47. CA and CAFB Connection to the GM Amplifier

Input and Output Capacitor Properties

Any good quality ceramic capacitors can be used with the

ADP7185 if they meet the minimum capacitance and maximum

ESR requirements. Ceramic capacitors are manufactured with a

variety of dielectrics, each with different behavior over temperature

and applied voltage. Capacitors must have a dielectric adequate to

ensure the minimum capacitance over the necessary temperature

range and dc bias conditions. X5R and X7R dielectrics with a

voltage rating from 6.3 V to 10 V are recommended. Due to their

poor temperature and dc bias characteristics, Y5V and Z5U

dielectrics are not recommended.

ADP7185ACPZN-R7 数据表(PDF) 15 Page - Analog Devices

ADP7185ACPZN-R7 数据表(HTML) 15 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

数据表下载