TS1582CM5(2003) データシートの表示（PDF） - TSC Corporation

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TS1582CM5
(Rev.:2003)

3A Dual Input Low Dropout Positive Voltage Regulator

TSC Corporation 

Application Information (continued)

The effect on output regulation can be seen in trace B

of Figure 3. It is important to note that the voltage drops

due to Rp are not eliminated; they will add to the

dropout voltage of the regulator regardless. The

TS1582 can control the voltage at the load as long as

the input-output voltage is greater than the total of the

dropout voltage of the device plus the voltage drop

across Rp

Figure 3. Remote Sensing Improves Load Regulation

Because they contain parasitic resistance and

inductance, capacitors are not ideal elements. These

parasitic elements dominate the change in output

voltage as the beginning of a transient load step

change. The ESR of the output capacitors produces

and instantaneous step in output voltage

∆V = ∆I (ESR). The ESL of the output capacitors

produces a drop proportional to the rate of change of

the output current V = L (∆I / ∆t). the output

capacitance produces a change in output voltage

proportional to the time until the regulator can respond

∆V = ∆t (∆I / C).

Figure 4. illustrates there transient effects.

Stability

The circuit design used in the TS1582 Series requires

the use of an output capacitor as part of the device

frequency compensation. The addition of 150uF

aluminum electrolytic or a 22uF solid tantalum on the

output will ensure stability for all operating conditions.

In order to meet the transient performance of the

processor larger value capacitors are needed. To limit

the high frequency noise generated by the processor

high quality bypass capacitors must be used. In order

to limit parasitic inductance (ESL) and resistance

(ESR) in capacitors to acceptable limits, multiple small

ceramic capacitors in addition to high quality solid

tantalum capacitors are required.

When the adjustment terminal is bypass to improve the

ripple rejection, the requirement for an output capacitor

increases. The Adjust pin is brought out on the fixed

voltage device specifically to allow this capability. To

further improve stability and transient response of

these devices larger values of output capacitor can be

used. The modern processors generate large high

frequency current transients. The load current step

contains higher order frequency components than the

output coupling network must handle until the regulator

throttles to the load current level.

Output voltage

The TS1582 (adjustable version) develops a 1.25V

reference voltage between the Sense Pin and the

Adjust Pin (Figure 5). Placing a resistor between these

two terminals causes a constant current to flow though

R1 and down though R2 to set the output voltage. In

general R1 is chosen so that this current is the

specified minimum load current of 10mA. The current

out of the Adjust pin is small, typically 50uA and it adds

to the current from R1.For best regulation the top of the

resistor divider should be connected directly to the

Sense pin.

Figure 5. Setting Output Voltage

TS1582 series

5-5

2003/12 rev. A

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