SMP402SC Просмотр технического описания (PDF) - Power Integrations, Inc

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производитель

SMP402SC

1-Watt Buck Regulator IC 20-72 VDC Input Non-isolated DC Output

Power Integrations, Inc 

SMP402

+

INPUT

-

D1

D2

4X

1N4002

C5

100 nF

D3

D4

R1

1.2 MΩ

R2

1.2 MΩ

R7

3.3 MΩ

R8

3.3 MΩ

L1

470 µH

C1

U1

1

2

3

4

5

6

7

8

R3

20.5 kΩ

R5

75 kΩ

D6

UF4002

16

15

14

13

12

C4-1 nF

11

10

C3

9

100 nF

R4

240 kΩ

C11

120 pF

JMP 1

C2

82 µF

R6

24.9 kΩ

VOUT

C6

100 nF

RTN

POLARITY

LEVEL

Figure 6. Schematic Diagram of a Non-isolated 5 V, 1 W ISDN Regulator Circuit Utilizing the SMP402.

PI-1455-042695

General Circuit Operation

The Buck DC-to-DC converter shown

in Figure 6 produces a single non-isolated

5 V, 1 W power supply. The high-

voltage P-channel MOSFET transistor

in the SMP402 is turned on and off at the

switching frequency. The ratio of ON-

time to the switching period is defined as

the duty cycle. The duty cycle changes

with input voltage to maintain a constant

average value of the switching

waveform. The switching waveform is

filtered by inductor L1 and capacitor C2

to produce the 5 V output. During the

MOSFET ON-time, the switch current

and inductor current ramp up at a linear

rate. During the P channel MOSFET

switch off time, the voltage across L1

reverses, forward biasing D6. Inductor

and diode current then ramp down

linearly until the MOSFET turns on

again. During normal operation,

inductor current ramps up and down

around the average value (I ), which is

OUT

actually the DC load current.

The 5 V output voltage is directly sensed

and accurately regulated by an internal

error amplifier. The error amplifier

generates an error signal which directly

controls the duty cycle of the integrated

high-voltage P-channel MOSFET

switch. The effective output voltage can

be fine-tuned by adjusting the resistor

divider formed by R5 and R6. Other

output voltages are possible (up to

approximately half the input voltage) by

changing the value of L1 as well as the

resistor divider.

Polarity of the DC input voltage can be

either positive or negative. D1, D2, D3,

and D4 “rectify” the DC input voltage to

provide a positive polarity input voltage

for the converter. C1 provides input

voltage filtering. The SMP402 contains

the integrated controller and high-voltage

P-channel MOSFET which, together

with D6, generates a pulse width

modulated switching AC voltage

waveform. L1 and C2 filter the AC

voltage to create the 5 V output. C6

filters high-frequency noise currents. R5

and R6 sense and divide the 5 V output

voltage for comparison with the internal

6D

1/96

bandgap reference voltage. C4 and R4

provide control loop compensation

feedback around the internal error

amplifier. C3 bypasses the onboard V

S

regulator. C11 sets the switching

frequency. R3 is fixed to set internal

currents accurately. C5 bypasses an

internally-generated, level-shifted bias

source of approximately 10 V, which is

referenced to the positive side of the

effective input voltage. This floating

supply is used for biasing the P-channel

MOSFET gate drivers. R1 and R2 sense

the level and polarity of the DC input

voltage. The current through R1 and the

SENSE+ input or R2 and the SENSE-

input must exceed 23 µA before the

converter will turn on. R7 and R8

provide hysteresis for the SENSE+ and

SENSE- inputs. Jumper JMP1 disables

the self-bias feature of the SMP402.

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