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NCP1031DR2

Low Power PWM Controller with On−Chip Power Switch and Startup Circuits for 48V Telecom Systems

ON Semiconductor 

NCP1030, NCP1031

GND

RSENSE

Internal Bias

Current Limit

Comparator

LEB

I1

CT Ramp

+

CT

50 mV

−

10 V

I2 = 3I1

+

3.0 V/3.5 V −

Error Amplifier

VFB

−

+

10 V +

2.5 V

−

I

One Shot

Pulse

O

−

+

PWM Comparator

S Reset Q

Dominant

R Latch

PWM Latch

COMP

2 kW

10 V

4.5 V

VDRAIN

+

7.5 V/10 V

−

Disable

ISTART

VCC

Thermal

Shutdown

16 V

Reset S

Q Dominant

Latch

+

10 V−

R

+

6.5 V

−

UV

+

10 V

2.5 V

−

OV

10 V

Figure 1. NCP1030/31 Functional Block Diagram

FUNCTIONAL PIN DESCRIPTION

Pin Name

Function

1 GND

Ground

2

CT

Oscillator Frequency

Selection

3

VFB

Feedback Input

4 COMP Error Amplifier Compensation

5

OV

Line Overvoltage Shutdown

6

UV

Line Undervoltage Shutdown

7

VCC

Supply Voltage

8 VDRAIN

Power Switch and

Startup Circuits

Description

Ground reference pin for the circuit.

An external capacitor connected to this pin sets the oscillator frequency up to 1 MHz.

The oscillator can be synchronized to a higher frequency by charging or discharging

CT to trip the internal 3.0 V/3.5 V comparator. If a fault condition exists, the power

switch is disabled and the frequency is reduced by a factor of 7.

The regulated voltage is scaled down to 2.5 V by means of a resistor divider.

Regulation is achieved by comparing the scaled voltage to an internal 2.5 V reference.

Requires external compensation network between COMP and VFB pins. This pin is

effectively grounded if faults are present.

Line voltage (Vin) is scaled down using an external resistor divider such that the OV

voltage reaches 2.5 V when line voltage reaches its maximum operating voltage.

Line voltage is scaled down using an external resistor divider such that the UV

voltage reaches 2.5 V when line voltage reaches its minimum operating voltage.

This pin is connected to an external capacitor for energy storage. During Turn−On, the

startup circuit sources current to charge the capacitor connected to this pin. When the

supply voltage reaches VCC(on), the startup circuit turns OFF and the power switch is

enabled if no faults are present. An external winding is used to supply power after

initial startup to reduce power dissipation. VCC should not exceed 16 V.

This pin directly connects the Power Switch and Startup Circuits to one of the

transformer windings. The internal High Voltage Power Switch Circuit is connected

between this pin and ground. VDRAIN should not exceed 200 V.

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