®

PWS750

7

6

5

7

PWS750-2U

2

3

4

3

6

PWS750-3U

4

1

Output

Gnd

0.3µF

–V

O

+V

O

Duplicate for Up to 8 Channels

User Option

10µH

0.3µF

Input

Gnd

14

12

10

EN

PWS750-1U

1

G

16

D

S

56

2N7002

T

T

3

7

11

V

D

IN

+V

+V

Ω

G

D

S

56

2N7002

Ω

G

D

S

2N7002

G

D

S

2N7002

0.3µF

0.3µF

PWS750-3U HIGH SPEED

DIODE BRIDGE PIN FUNCTIONS

The AC pins are tied directly to the AC pins of the PWS750-

2U. The +V and –V pins are rectified output voltages. The

filter capacitors must be located as close as possible to these

pins to minimize series inductance and therefore noise.

Bypass capacitors will be needed at each device in the

circuit.

BASIC OPERATION

SINGLE CHANNEL OPERATION,

PC BOARD LAYOUT CONSIDERATIONS

A simple two-layer board can be used on single channel

applications to create a DC/DC converter with low radiated

noise. A ground plane should be located directly under both

the input and the output components for optimum ground

return paths. The surface mount components make it easy to

design with a ground plane. The output filter capacitors

should be located as close to the PWS750-3U as possible. A

sample layout is shown in Figure 1.

For multiple channel applications, T and T traces must have

minimum capacitive loading. Therefore, there should be no

ground plane (or power plane) under these two traces. The

driver signal is a 4-6V low current 800kHz signal, which

will generate little radiated noise if the traces are kept short.

MULTIPLE CHANNEL OPERATION

The oscillator can drive up to four-channels (eight FETs)

directly when operating at 10-18V. A 10

Ω resistor must be

placed in series with T and T to stabilize the FET gate

charging. For more than four-channel operation, or 5V-

multiple-channel operation, the driver circuit needs a FET

booster circuit, as shown in Figure 2. Large gate drive surge

currents (>100mA) are needed to turn on the gates.

If the total output current drawn by all the channels exceeds

250mA, then it will be necessary to circumvent the current

supply.

5V OPERATION

With 5V operation, the transformer winding current ratio is

3:1, therefore generating much greater currents in the pri-

mary. The input ripple voltage will be larger, so an input pi

filter will be necessary to isolate the converter noise from the

rest of the circuit. For example, when the output is

±15mA

the input current will be at least 120mA.

MOSFET

MAX DRIVE CURRENT

PACKAGE

BREAKDOWN

TN0604

4A

TO-92

40V

2N7002

115mA

SO-T23

60V

2N7008

500mA

TO-92

60V

2N7010

1.3A

TO-237

60V

2N7012

1.2A

4-Pin DIP

60V

TABLE I. MOSFET Selector Guide.

FIGURE 2. MOSFET Driver Booster Circuits.