AND8079 datasheet(5/20 Pages) ONSEMI

No de pièce	AND8079

Description	A Low Cost DDR Memory Power Supply Using the NCP1571 Synchronous Buck Converter and a LM358 Based Linear Voltage Regulator

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Fabricant	ONSEMI [ON Semiconductor]

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AND8079/D

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5

Schottky Diode for Synchronous MOSFET

The efficiency of the buck converter can be improved

slightly by placing a Schottky diode (D1) in parallel with the

bottom MOSFET (Q3). The body diode of Q3 is used to

conduct current during the non-overlap time when both the

top (Q2) and bottom (Q3) MOSFETs are turned OFF. But

because the non-overlap time is only approximately 50 ns

for the NCP1571’s 200 kHz switching speed, the efficiency

savings

will

be

only

approximately

1.0%.

The

demonstration board included a provision for D1; however,

the performance of the circuit was not testing with this

diode.

Experimental Results

The experimental results of the demonstration PCB are

shown in Figures 4 through 20. Figure 3 shows the test setup

used to create the current load transients for the Vtt supply

voltage. The transient current load tests for the Vdd and Vtt

supply voltages were created using a Kikusui Electronic

Load Controller. Unless noted, the standard test conditions

are as listed below:

1. Ambient Temperature = 23

_C

2. Vdd Current Load (IVdd) = 8.0 A

3. Vtt Current Load (IVtt) = 1.25 A source load

4. VREF Current Load (IREF) = 2.5 mA

5. 5.0 V Input Voltage = 5.00 V

6. 12 V Input Voltage = 12.00 V

7. -12 V Input Voltage = -12.00 V

Figure 3. Vtt Transient Load Test Setup for a 2.0 A Sink to 2.0 A Source Test

2.5 V

Vdd

R7

OUT

-

+

-

+

Q4

U2A

VREF

Q5

C22

+

C23

+

Vtt

Vtt DDR Circuit

2.0 A

DC Current Source

Pulsating Current Source

Pulse Width = 100 ms

Period = 200 ms

l1 = 0 A

l2 = 4.0 A

Rise Time = 50

ms

Fall Time = 50

ms

Vtt Circuit

DC Current Source

Pulsating Current Source

0 A

2 .0 A

2.0 A

Vtt

2.0 A Current Sink Test

Vtt Circuit

DC Current Source

Pulsating Current Source

4 A

Vtt

2.0 A Current Source Test

2 .0 A

2.0 A

+

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