DP2525C datasheet(9/11 Pages) ETC

9 / 11 page

DP2525

Low Cost Primary Side Regulation(PSR) PWM Power Switch

9/11

Rev.2.0

Fig.4

Programmable

Cable

Drop

Compensation (CDC) in CV Mode

In smart phone charger application, the battery is

always connected to the adapter with a cable wire

which can cause several percentages of voltage

drop on the actual battery voltage. In DP2525, an

offset voltage is generated at FB pin by an internal

current source (modulated by CDC block, as shown

in Fig.5) flowing into the resistor divider. The

current is proportional to the switching period, thus,

it is inversely proportional to the output power Pout.

Therefore, the drop due the cable loss can be

compensated. As the load decreases from full

loading to zero loading, the offset voltage at FB pin

will increase. By adjusting the resistance of R1 and

R2 (as shown in Fig.), the cable loss compensation

can be programmed. The percentage of maximum

compensation is given by

(

)

100

R1//R2

Icable_max

Vout

V(cable)

FB_REF

≈

∆

For

example,

R1=3K

Ω , R2=18K Ω , The

percentage of maximum compensation is given by:

(

)

100

3K//18K

60uA

Vout

V(cable)

∆

Naux

KP211

Sample &

Hold

Icable

CDC

Icable

Pout

60uA

Modulated by CDC

Fig.5

Optimized Dynamic Response

In DP2525, the dynamic response performance is

optimized to meet USB charge requirements.

Audio Noise Free Operation

As mentioned above, the multi-mode CV control

with a hybrid of FM and AM provides frequency

modulation. An internal current source flowing to

CS pin realizes CS peak voltage modulation. In

DP2525, the optimized combination of frequency

modulation and CS

peak

voltage modulation

algorithm can provide audio noise free operation

from full loading to zero loading.

Dynamic BJT Base Drive

DP2525 drives a power BJT with dynamic base

drive control to optimize efficiency. The BJT base

drive current ranges from 10mA to 30mA (typical),

and is dynamically controlled according to the

power supply load change. The higher the output

power, the higher the based current. Specifically,

the base current is related to CS peak voltage, as

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