NIS6201 데이터 시트보기 (PDF) - ON Semiconductor

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NIS6201

Floating, Regulated Charge Pump

ON Semiconductor 

NIS6201

The overcharge comparator detects when the voltage at

Vreg is 10% greater than its set level. If this situation

occurs, the overcharge circuit overrides the oscillator and

turns on the bottom FET of the driver stage. This shunts the

start−up current directly to ground and bypasses the

capacitor on Vreg thus allowing for safe start−ups at high

input voltages.

Oscillator

The oscillator in this chip operates at a nominal

frequency of 1 MHz. The FETs have an on resistance of

20 W and can drive loads in excess of 20 mA. Since the

charge diodes and capacitors are external, this device can

drive a “floating” voltage that is referenced to the input bus

such as is shown in Figure 7. The “isolation” voltage for the

regulated output is limited only by the ratings of these

external components. The oscillator can also drive a

conventional voltage doubler circuit or an inverting output

stage.

Total Power Consumption

The SO−8 package used for this chip has a power rating

of 570 milliwatts. The major losses in this device come

from three circuits plus the bias current. These are the

following:

Shunt Diode

The power dissipated in this diode is due to the current

through the input series resistor when the input exceeds 15

volts. The current in the diode is the current through the

input resistor less the output and bias currents in the chip.

The output current is equal to the load current unless

multiple pump stages are used in which case it is multiplied

by the number of stages in use. An additional 2 mA of bias

current is required to operate the charge pump.

Pshunt diode +

ƪǒ Ǔ ƫ VCC @

(Vin * VCC)

Rseries

* 2 mA * (Iout @ nstages)

LDO

The power lost in the LDO pass transistor is calculated

by the voltage drop across it and the current through it. As

was the case with the shunt diode, when calculating the

load current, the number of pump stages must be accounted

for.

PLDO + (VCC * Vreg) @ (2mA ) (Iout @ nstages))

Oscillator

The power dissipated in the oscillator section can be

approximated by multiplying the square of the load current

by the typical on resistance.

POsc + Iout2 @ 20 W

Bias Current

The bias current is simply the input voltage at the Vcc pin

multiplied by 2 mA.

The total power dissipated by the chip is the sum of these

four losses. If the input voltage does not exceed 15 volts,

the shunt diode losses can be ignored. The sum of these

losses should not exceed the power rating for the device.

Note that the power rating is specified at 25°C and must be

derated at higher operating temperatures.

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