APU3039 View Datasheet(PDF) - Advanced Power Electronics Corp

Part Name

Description

Manufacturer

APU3039

SYNCHRONOUS PWM CONTROLLER WITH OVER CURRENT PROTECTION

Advanced Power Electronics Corp 

Advanced Power

Electronics Corp.

APU3039

Feedback VREF

voltage 0.4V

FS(NOM)

IOUT

Switching

frequency

High Side MOSFET

turn on time (tON)

VOUT

FS(NOM)3 VIN

IOUT

DMAX/FS(NOM)

IOUT

Average Inductor

Current

<IL>=IOUT

Normal

IO(LIM)

IO(MAX)

IOUT

Over Current Shutdown

operation

Limit Mode by UVLO

From Figure 7, the average inductor current during the

current limit mode is:

IO(LIM) = ISET +

∆IPK-PK(LIM)

2

---(4)

The inductor's ripple current can be expressed as:

∆IPK-PK(LIM)

=

(VIN - VOUT) x VOUT

VIN x Lx fS

Combination of above equation and (4) results in:

( ) ISET = IO(LIM) -

(VIN-VOUT)xVOUT

2 xfS x L xVIN

---(5)

Combination of equations (5) and (2) results in the rela-

tionship between RSET and output current limit.

[ ( )] RSET =

RDS(ON)

IOCSET

x

IO(LIM) -

(VIN-VOUT)xVOUT

2xfS x LxVIN

---(6)

Figure 6 - Diagram of over-current operation.

Operation in current limit is shown in Figure 7, the high

side MOSFET is turned off and inductor current starts to

decrease. Because the output inductor current is higher

than the current limit setpoint (ISET), the over-current com-

parator keeps high until the inductor current decreases

to be below ISET. Then another cycle starts.

During over-current mode, the valley inductor current is:

iL(VALLEY) = ISET

The peak inductor current is given as:

IL(PEAK) = ISET+(VIN-VOUT) x tON/L

---(3)

To avoid undesirable trigger of over-current protection,

this relationship must be satisfied:

ISET /

IO(NOM)

-

∆IPK-PK(NOM)

2

Inductor iL(PEAK)

Current iL(AVG)

ISET=iL(VALLEY)

Where:

IO(LIM) = The Output Current Limit. Typical is 50%

higher than nominal output current

VIN = Maximum Input Voltage

VOUT = Output Voltage

fS = Switching Frequency

L = Output Inductor

RDS(ON) = RDS(ON) of Low Side MOSFET

IOCSET = OC Threshold Set Current

From the above analysis, the current limit is not only

dependent on the current setting resistor RSET and RDS(ON)

of low side MOSFET but it is also dependent on the

input voltage, output voltage, inductance and switching

frequency as well.

The cycle-by-cycle over-current limit will hold for a cer-

tain amount of time, until the output voltage drops below

0.4V, the under-voltage lock out activates and latches

off the output driver. The operation waveform is shown in

Figure 7. Normal operation will resume after APU3039 is

powered up again.

Current Limit

Comparator Output

HDrv

tON

tOFF

Figure 7 - Operation waveforms during current limit.

7

Share Link: