wound isolation transformers using a ferrite core.
They are encapsulated in plastic packages, allowing a
high isolation voltage rating.
The PWS750-3U is a high-speed monolithic diode
bridge in a plastic 8-pin SO package.
One PWS750-1U can be used to drive up to four
channels (15V nominal operation). One PWS750-2U
and PWS750-3U and two 2N7002 (surface mount) or
2N7008 (TO-92) MOSFETs made by Siliconix are
used per isolated channel. When a PWS750-4U is
used as the transformer (5V input), then two TN0604s
made by Supertex must be used, due to the higher
currents of the primary (lower RDS on) and the lower
V
GS
threshold. With 5V operation only one channel
can be directly driven by the PWS750-1U (a simple
FET booster circuit can be used for multichannel
operation; see Figure 3).
2N7002
(2)
or
2N7008
D
G
S
6
0.3µF
Soft
Start
14
TTL
IN
Typical Connection for
Internal Oscillator Operation
DESCRIPTION
The PWS750 consists of three building blocks for
building a low cost DC/DC converter. With them you
can optimize DC/DC converter PC board layout or
build a multichannel isolated DC/DC converter. All
parts are surface mount, requiring minimal space to
build the converter. The modular design minimizes the
cost of isolated power.
The PWS750-1U is a high-frequency (800kHz nomi-
nal) driver that can drive N-channel MOSFETs up to
the size of a 1.3A 2N7010. The recommended
MOSFET for individual transformer drivers is the
2N7008. The PWS750-1U is supplied in a 16-pin
double-wide SO package.
PWS750 SINGLE-CHANNEL CONNECTION
10µH
(1)
+V
+V
IN
7
PWS750-1U
Reference
Comparator
1
R
S
Driver
Differential
Amplifier
Oscillator
16
T
10
Enable
10Ω
(3)
PWS750-2U
5
4
3
3
6
1
PWS750-3U
4
10Ω
(3)
T
V
D
3
11
0.3µF
Input
Gnd
D
G
S
7
2
12
TTL
OUT
Output
(2)
2N7002
Ground
or
2N7008
Duplicate for multichannel
operation with PWS750-2U.
0.3µF
0.3µF
10Ω
–V
O
(1)
10Ω
+V
O
(1)
NOTES: (1) User option. (2) Use TN0604 for 5V to
±15V
operation. (3) Multichannel Operation.
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
rated, fail on 5pC partial discharge leakage current on five successive pulses at 60Hz.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
®
PWS750
2
PIN CONFIGURATIONS
PWS750-1U
T
1
2
V
D
3
4
5
6
+V
IN
7
8
16
15
14 TTL
IN
13
12 TTL
OUT
11 Gnd
10 Enable
9
NC
AC
16-Pin SO Double-Wide
Surface Mount
1
2
8 NC
7 T
O
6 V
D
5 T
O
8-Pin DIP
Surface Mount
AC
+V
T
–V
1
2
3
4
8-Pin SO
Surface Mount
PWS750-2U
PWS750-4U
PWS750-3U
8
7
6 AC
5
ABSOLUTE MAXIMUM RATINGS
Supply Voltage ..................................................................................... 18V
Junction Temperature ...................................................................... 150°C
Storage Temperature ........................................................ –40°C to +85°C
Lead temperature (soldering, SOIC, 3s) ........................................ +260°C
Max Load, Sum of Both Outputs (PWS750-2U, 4U) ......................... 60mA
ORDERING INFORMATION
PWS750-XU
Basic Model Number
Components
1U : High-Frequency Driver
2U, 4U : Isolation Transformer
3U : High-Speed Monolithic Diode Bridge
Gnd 3
AC
4
PACKAGE INFORMATION
PRODUCT
PWS750-1U
PWS750-2U
PWS750-3U
PWS750-4U
PACKAGE
16-Pin SOIC
8-Pin Plastic
8-Pin SO
8-Pin Plastic
PACKAGE DRAWING
NUMBER
(1)
211
226
182
226
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book.
®
3
PWS750
TYPICAL PERFORMANCE CURVES
T
A
= +25°C, V
IN
= 15VDC, I
LOAD
=
±15mA
unless otherwise noted.
PWS750-4U LINE REGULATION
5.4
5.3
5.2
5.1
Input (V)
Input (V)
PWR750-2U LINE REGULATION
18
16
5
4.9
4.8
4.7
4.6
13
14
15
±V
OUT
(V)
16
17
18
14
12
10
10
12
14
±V
OUT
(V)
16
18
PWR750-2U AND PWS70-4U LOAD LINES
50
OUTPUT RIPPLE VOLTAGE
Ripple Voltage (mVp-p)
20
±V
OUT
(V)
40
Ripple Frequency =
Oscillator Frequency
30
PWS750-2U
15
20
10
PWS750-4U
10
0
5
10
15
Load (mA)
20
25
30
0
0.1
0.2
0.4
0.6
0.8
1
Filter Capacitance (µF)
EFFICIENCY/LOAD CURVE
80
PWS750-4U
70
Efficiency (%)
TTL
IN
SIGNAL DUTY CYCLE
100
75
60
4 Channel
PWS750-1U
PWS750-2U
40
% Duty Cycle
Acceptable
Duty
Cycle
t
H
t
L
DC =
t
H
%
t
H
+ t
L
50
50
25
Nominal Operating
Frequency
0
30
0
5
10
15
20
25
30
Load Current (±mA)
1
1.5
2
2.5
Synchronization Frequency (MHz)
(= Twice the FET Drive Frequency)
®
PWS750
4
TYPICAL PERFORMANCE CURVES
(CONT)
T
A
= +25°C, V
IN
= 15VDC, I
LOAD
=
±15mA
unless otherwise noted.
THE OUTPUT VOLTAGE CAN BE ADJUSTED
±3% BY VARYING THE DRIVER FREQUENCY
16
OUTPUT VOLTAGE DRIFT WITH A ±15mA LOAD
15.5
15.25
V
OUT
(V)
15.5
±V
OUT
(V)
15
15
14.75
14.5
14.5
–25
0
25
50
75
100
Temperature (°C)
14
1
1.5
1.6
2
TTL
IN
Frequency (MHz)
THEORY OF OPERATION
The PWS750 components are basic building blocks to be
used with other standard components to build an isolated
push-pull DC/DC converter. The oscillator runs at 800kHz
nominal, making it possible to reduce the size of the trans-
former and lower the output ripple voltage.
PWS750-1U OSCILLATOR PIN FUNCTIONS
TTL
IN
is used to control the driver frequency with an
external TTL level frequency source. The input frequency
must be twice the desired driver frequency, since there is an
internal divide-by-2 circuit to produce a 50% duty cycle
output. The input duty cycle can vary from 12% to 95% (see
Typical Performance Curves). When in the free running
mode, the TTL
IN
pin must be tied to ground.
TTL
OUT
is used when it is desired to synchronize the outputs
of multiple PWS750-1Us to minimize beat frequency prob-
lems. A standard open collector output is provided, therefore
a 330Ω to 3.3kΩ pull-up resistor will be necessary depend-
ing on stray capacitance on the sync line. A maximum of
eight PWS750-1Us can be connected without the use of an
external TTL buffer.
An Enable pin is provided so that the driver (T, T) can be
shut down to minimize power use if required. A TTL low
applied to the pin will shut down the driver within one cycle.
A TTL high will enable the driver within one cycle. The
TTL
OUT
will still have an 800kHz signal when a master
driver is disabled, so other synchronized drivers will not be
shut down. The pin can be left open for normal operation.
The +V
IN
pin supplies power to the oscillator. The V
D
pin
connects the power to the transformer through the internal
overcurrent sense resistor. The other end of the overcurrent
sense resistor is tied to +V
IN
. A 0.3µF bypass capacitor must
be connected to the V
D
pin to reduce the ripple current
through the shunt resistor; otherwise false current limit
conditions can occur due to ripple voltage peaks.
During overload conditions the output drive shuts off for
approximately 80µs, then turns back on for 20µs, resulting
in a 25% power up duty cycle. If the overload condition still
exists, then the output will shut off again. When the fault or
the excessive load is removed, the converter resumes normal
operation.
The T and T pins are the complementary FET drive outputs
and are tied directly to the corresponding FET gate. The
connection must be as short as possible. For multiple chan-
nel operation they cannot be located above any ground or
power planes, because capacitive loading will not allow fast
enough charging of the FET gate.
PWS750-2U AND PWS750-4U
TRANSFORMER PIN FUNCTIONS
On the primary side the V
D
pin of the PWS750-2U is tied
directly to the V
D
pin of the PWS750-1U. Remember to
place a 0.1µF capacitor as close to the PWS750-2U V
D
pin
as possible. The T
O
and T
O
pins are connected to the drains
of the corresponding FETs, whose sources are connected to
ground. On the secondary side of the transformer, the Gnd
pin is tied directly to the isolated ground. AC pins are
800kHz square wave signals at twice the output voltage, and
are connected directly to the corresponding pin on the
PWS750-3U. Pins 2 and 4 can be interchanged for ease of
hook up. The connection to the diode bridge must be as
direct as possible to minimize radiated noise.
The winding ratio for the PWS750-2U is 1:1. This means
that the output would normally be less than the input due to
voltage drops in the FETs, transformer and diode bridge.
Since the DC/DC converter is operating at 800kHz, the
transformer is starting to operate close to the resonant
frequency, which causes the output to increase in magni-
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