AP3598A

Document number: DS37261 Rev. 2 - 2

13 of 28

www.diodes.com

November 2014

© Diodes Incorporated

AP3598A

A Product Line of

Diodes Incorporated

6. Current Balance

The AP3598A extracts phase currents for current balance by parasitic on-resistance of the lower switches when turned on as shown in Figure 2.

Sample

&Hold

Current

Balance

_

+

Reference

Voltage

+

_

PHASE

The GM amplifier senses the voltage drop across the lower switch and converts it into current signal when it turns on. The sampled and held

current is expressed as:

A

12

10

R

I

I

3

)

ON

(

DS

LX

CSX













offset voltage of the current sensing circuit.

The AP3598A tunes the duty cycle of each channel for current balance according to the sensed inductor current signals as shown in Figure 3. If

the current of channel 1 is smaller than the current of channel 2, the AP3598A increases the duty cycle of the corresponding phase to increase its

phase current accordingly, vice versa.

+

_

+

_

PWM1

PWM2

COMP

+

_

+

RAMP1

RAMP2

Figure 3. Current Balance Scheme of AP3598A

7. Power Saving Interface (PSI)

This is a multilevel input to support Power Saving features. The AP3598A supports dual phase with FCCM and single phase with DCM and FCCM.

Mode

Descriptions

DCM

Discontinuous Conduction Mode decreases the switching frequency to improve the efficiency at light load

FCCM

Forced Continuous Conduction Mode does not change the switching frequency when the inductor current

goes to negative at light load. This mode is used to disable Power Saving features

Table 2. Description of Operating Modes

As shown in Table 2, an input high voltage (>1.5V) will set the controller to dual phase with FCCM mode; an input of intermediate level (between

0.8V and 1.1V) will set the controller to single phase with FCCM mode; an input low voltage will set the controller to single phase with DCM mode.