ZLDO500 Просмотр технического описания (PDF) - Zetex => Diodes

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производитель

ZLDO500

5.0 VOLT ULTRA LOW DROPOUT REGULATOR

Zetex => Diodes 

ZLDO500

1). Operation From A Low Voltage

Battery Pack

Fig.1 shows the ZLDO500 regulator being

used to stabilise the output of a 6V battery

pack. The ultra low dropout voltage of only

100mV at full load (300mA) given by the

regulator allows the minimum number of

cells to be used in the pack and also

maximises the energy that can be removed

from the battery before the output of the

ZLDO500

LBF Spg

SC Gnd

Vin D/C

N/C Vout

C1

10pF

+5V

6V

C3

100nF

C2

1uF

Output

0V

Figure 1

regulator starts to fail.

At a load current of 100mA the dropout

voltage falls to around 30mV. The endurance

of the battery pack is not only dependent on

dropout voltage. When operating, some low

dropout regulators can consume high

quiescent currents, sometimes approaching

as much as a tenth of their maximum load

current specification when approaching

APPLICATIONS

dropout conditions. Despite its 300mA output

rating, when enabled the ZLDO500 consumes

typically only 630uA regulating normally and

3mA when the input falls too low for

regulation.

2). Post Converter Regulation

A common problem with multiple output

switch mode converters is that only one

output can be used in the feedback control

loop of the switching regulator. Thus only

one output is fully regulated. All other

outputs are prone to tracking errors that

occur if the load on any output change

significantly. By ensuring close coupling of all

transformer windings and minimising the

impedance of all outputs, these errors can be

reduced but never eliminated. A simple way

round this problem is to wind the switching

regulator transformer to give a slightly higher

voltage than required and regulate down

from this to the desired voltage with a linear

regulator. This is indicated in Figure 2. To

keep losses low and so maintain the

advantages of a switch mode supply, it is

important that the voltage drop across this

regulator is kept as low as possible, i.e. just

high enough to compensate for the poor

output impedance of the switching power

supply but no higher. The low dropout

Voltage

Feedback

D1

+ 12V Out

TR1

Switching

Regulator

Figure 2

C4

220uF

D2

ZLDO500

LBF Spg

SC Gnd

Vin D/C

N/C Vout

C5

2 2 0 uF

4-85

C1

10pF

+ 5.0V Out

C2

1uF

0V Out

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