NCP1547 데이터 시트보기 (PDF) - ON Semiconductor

부품명

상세내역

일치하는 목록

NCP1547

1.5 A, 340 kHz, Buck Regulator with Synchronization Capability

ON Semiconductor 

NCP1547

oscillation, as shown in Figure 8. Similar to current mode

control, this oscillation occurs at the duty cycle greater than

50% and can be alleviated by using a larger inductor value.

The current limit threshold is reduced to Foldback Current

when the FB pin falls below Foldback Threshold. This

feature protects the IC and external components under the

power up or over−load conditions.

Figure 8. The Regulator in Current Limit

BOOST Pin

The BOOST pin provides base driving current for the

power switch. A voltage higher than VIN provides required

headroom to turn on the power switch. This in turn reduces

IC power dissipation and improves overall system

efficiency. The BOOST pin can be connected to an external

boost−strapping circuit which typically uses a 0.1 mF capacitor

and a 1N914 or 1N4148 diode, as shown in Figure 1.

When the power switch is turned on, the voltage on the

BOOST pin is equal to

VBOOST + VIN ) VO * VF

where:

VF = diode forward voltage.

The anode of the diode can be connected to any DC

voltage as well as the regulated output voltage (Figure 1).

However, the maximum voltage on the BOOST pin shall not

exceed 40 V.

As shown in Figure 9, the BOOST pin current includes a

constant 7.0 mA pre−driver current and base current

proportional to switch conducting current. A detailed

discussion of this current is conducted in Thermal

Consideration section. A 0.1 mF capacitor is usually

adequate for maintaining the Boost pin voltage during the on

time.

30

25

20

15

10

5

00

0.5

1.0

1.5

SWITCHING CURRENT (A)

Figure 9. The Boost Pin Current Includes 7.0 mA

Pre−Driver Current and Base Current when the

Switch is Turned On. The Beta Decline of the

Power Switch Further Increases the Base

Current at High Switching Current

Shutdown

The internal power switch will not turn on until the VIN

pin rises above the Startup Voltage. This ensures no

switching will occur until adequate supply voltage is

provided to the IC. Refer to Figure 10 for the SHDNB

(shutdown−bar) pin input circuit.

SHDNB

VIN

20k

±33%

-

1.2V +

VZ = 6V to 8V

Figure 10.

GND

The IC enters a sleep mode when the SHDNB pin is pulled

below the Shutdown Threshold Voltage. In sleep mode, the

power switch is kept open and the supply current reduces to

Shutdown Quiescent Current (1 mA typically). This pin has

an internal pull−down current. When not in use, pull this pin

up to VCC with a resistor (See Figure 1). A 100 kW pullup

resistor will ensure safe operation from below 9 V and

during a 40 V load dump condition.

http://onsemi.com

8

Share Link: