ADP2105ACPZ-3.3-R7 datasheet(13/32 Pages) AD

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ADP2105/ADP2106/ADP2107

Rev. 0 | Page 13 of 32

SLOPE COMPENSATION

Slope compensation stabilizes the internal current control loop

of the ADP2105/ADP2106/ADP2107 when operating beyond

50% duty cycle to prevent sub-harmonic oscillations. It is imple-

mented by summing a fixed scaled voltage ramp to the current

sense signal during the on-time of the P-channel MOSFET switch.

The slope compensation ramp value determines the minimum

inductor that can be used to prevent sub-harmonic oscillations

at a given output voltage. The slope compensation ramp values

for ADP2105/ADP2106/ADP2107 follow. For more information,

see the Inductor Selection section.

For the ADP2105:

Slope Compensation Ramp Value = 0.72 A/μs

For the ADP2106:

Slope Compensation Ramp Value = 1.07 A/μs

For the ADP2107:

Slope Compensation Ramp Value = 1.38 A/μs

FEATURES

Enable/Shutdown

Drive EN high to turn on the ADP2105/ADP2106/ADP2107.

Drive EN low to turn off the ADP2105/ADP2106/ADP2107,

reducing input current below 0.1 μA. To force the ADP2105/

ADP2106/ADP2107 to automatically start when input power

is applied, connect EN to IN. When shut down, the ADP2105/

ADP2106/ADP2107 discharge the soft start capacitor, causing

a new soft start cycle every time they are re-enabled.

Synchronous Rectification

In addition to the P-channel MOSFET switch, the ADP2105/

ADP2106/ADP2107 include an integrated N-channel MOSFET

synchronous rectifier. The synchronous rectifier improves

efficiency, especially at low output voltage, and reduces cost and

board space by eliminating the need for an external rectifier.

Current Limit

The ADP2105/ADP2106/ADP2107 have protection circuitry to

limit the direction and amount of current flowing through the

power switch and synchronous rectifier. The positive current

limit on the power switch limits the amount of current that can

flow from the input to the output, while the negative current

limit on the synchronous rectifier prevents the inductor current

from reversing direction and flowing out of the load.

Short Circuit Protection

The ADP2105/ADP2106/ADP2107 include frequency foldback

to prevent output current run-away on a hard short. When the

voltage at the feedback pin falls below 0.3 V, indicating the possi-

bility of a hard short at the output, the switching frequency is

reduced to 1/4 of the internal oscillator frequency. The reduction

in the switching frequency gives more time for the inductor to

discharge, preventing a runaway of output current.

Undervoltage Lockout (UVLO)

To protect against deep battery discharge, undervoltage lockout

circuitry is integrated on the ADP2105/ADP2106/ADP2107.

If the input voltage drops below the 2.2 V UVLO threshold, the

ADP2105/ADP2106/ADP2107 shut down, and both the power

switch and synchronous rectifier turn off. Once the voltage rises

again above the UVLO threshold, the soft start period is initiated,

and the part is enabled.

Thermal Protection

In the event that the ADP2105/ADP2106/ADP2107 junction

temperatures rise above 140°C, the thermal shutdown circuit turns

off the converter. Extreme junction temperatures can be the

result of high current operation, poor circuit board design, and/or

high ambient temperature. A 40°C hysteresis is included so that

when thermal shutdown occurs, the ADP2105/ADP2106/

ADP2107 do not return to operation until the on-chip tempera-

ture drops below 100°C. When coming out of thermal

shutdown, soft start is initiated.

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 the soft start

capacitor (CSS) from SS to AGND. When the ADP2105/ADP2106/

ADP2107 are disabled, or if the input voltage is below the under-

voltage lockout threshold, CSS is internally discharged. When the

ADP2105/ADP2106/ADP2107 are enabled, CSS is charged through

an internal 0.8 μA current source, causing the voltage at SS to rise

linearly. The output voltage rises linearly with the voltage at SS.

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