ADP2105ACPZ-3.3-R7 datasheet(18/32 Pages) AD

18 / 32 page

ADP2105/ADP2106/ADP2107

Rev. 0 | Page 18 of 32

INPUT FILTER

The IN pin is the power source for the ADP2105/ADP2106/

ADP2107 internal circuitry, including the voltage reference and

current sense amplifier that are sensitive to power supply noise.

To prevent high frequency switching noise on the PWIN pins from

corrupting the internal circuitry of the ADP2105/ADP2106/

ADP2107, a low-pass RC filter should be placed between the IN

pin and the PWIN1 pin. The suggested input filter consists of

a small 0.1 μF ceramic capacitor placed between IN and AGND

and a 10 Ω resistor placed between IN and PWIN1. This forms

a 150 kHz low-pass filter between PWIN1 and IN that prevents

any high frequency noise on PWIN1 from coupling into the

IN pin.

SOFT START

The ADP2105/ADP2106/ADP2107 include soft start circuitry

to limit the output voltage rise time to reduce inrush current at

startup. To set the soft start period, connect a soft start capacitor

(CSS) from SS to AGND. The soft start period varies linearly

with the size of the soft start capacitor, as shown in the

following equation:

TSS = CSS × 109 ms

To get a soft start period of 1 ms, a 1 nF capacitor must be

connected between SS and AGND.

LOOP COMPENSATION

The ADP2105/ADP2106/ADP2107 utilize a transconductance

error amplifier to compensate the external voltage loop. The

open loop transfer function at angular frequency, s, is given by

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

OUT

REF

OUT

COMP

)

(

)

(

where:

VREF is the internal reference voltage (0.8 V).

VOUT is the nominal output voltage.

ZCOMP(s) is the impedance of the compensation network at the

angular frequency, s.

COUT is the output capacitor.

Gm is the transconductance of the error amplifier (50 μA/V

nominal).

GCS is the effective transconductance of the current loop.

GCS = 1.875 A/V for the ADP2105.

GCS = 2.8125 A/V for the ADP2106.

GCS = 3.625 A/V for the ADP2107.

The transconductance error amplifier drives the compensation

network that consists of a resistor (RCOMP) and capacitor (CCOMP)

connected in series to form a pole and a zero, as shown in the

following equation:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ +

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

COMP

)

(

At the crossover frequency, the gain of the open loop transfer

function is unity. This yields the following equation for the

compensation network impedance at the crossover frequency:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

REF

OUT

CROSS

COMP

)

(

)

(

where:

FCROSS = 80 kHz, the crossover frequency of the loop.

COUTVOUT is determined from the Output Capacitor Selection

section.

To ensure that there is sufficient phase margin at the crossover

frequency, place the Compensator Zero at 1/4 of the crossover

frequency, as shown in the following equation:

)

(

⎟

⎠

⎞

⎜

⎝

⎛

COMP

CROSS

Solving the above two simultaneous equations yields the value

for the compensation resistor and compensation capacitor, as

shown in the following equation:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

REF

OUT

CROSS

COMP

)

(

COMP

CROSS

COMP

ADP2105ACPZ-3.3-R7 数据表(PDF) 18 Page - Analog Devices

ADP2105ACPZ-3.3-R7 数据表(HTML) 18 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

数据表下载

链接网址

ADP2105ACPZ-3.3-R7 数据表(PDF) 18 Page - Analog Devices

ADP2105ACPZ-3.3-R7 数据表(HTML) 18 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

数据表 下载

链接网址

数据表下载