SPX1129M3-2.5 Просмотр технического описания (PDF) - Signal Processing Technologies

Номер в каталоге

Компоненты Описание

производитель

SPX1129M3-2.5

500mA Low Dropout Voltage Regulator

Signal Processing Technologies 

SPX1129

Note 1: Output or reference voltage temperature coefficients defined as the worst-case voltage change divided by the total temperature range.

Note 2: Unless otherwise specified all limits are guaranteed for TJ = 25°C, VIN = 6V, IL = 100µA and CL = 1µF. Additional conditions for the 8-pin versions are

feedback tied to 5V tap and output tied to output sense (VOUT = 5V) and VSHUTDOWN ≤ 0.8V.

Note 3: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are

covered under the specification for thermal regulation.

Note 4: Line regulation for the SPX1129 is tested at 150°C for IL = 1 mA. For IL = 100µA and TJ = 125°C, line regulation is guaranteed by design to 0.2%. See

typical performance characteristics for line regulation versus temperature and load current.

Note 5: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value measured at 1V differential at

very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V over temperature) must be taken into account.

Note 6: Comparator thresholds are expressed in terms of a voltage differential at the feedback terminal below the nominal reference voltage measured at 6V input. To

express these thresholds in terms of output voltage change, multiply by the error amplifier gain = VOUT/VREF = (R1 + R2)/R2. For example, at a programmed output

voltage of 5V, the Error output is guaranteed to go low when the output drops by 95 mV x 5V/1.235 = 384 mV. Thresholds remain constant as a percent of VOUT as

VOUT is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.

APPLICATION HINTS

EXTERNAL CAPACITORS

The stability of the SPX1129 requires a 2.2µF or greater

capacitor between output and ground. Oscillation could occur

without this capacitor. Most types of tantalum or aluminum

electrolytic works fine here. For operations of below -25°C solid

tantalum is recommended since the many aluminum types have

electrolytes the freeze at about -30°C. The ESR of about 5Ω or

less and resonant frequency above 500kHz are the most

important parameters in the value of the capacitor. The capacitor

value can be increased without limit.

At lower values of output current, less output capacitance is

required for stability. For the currents below 10mA the value of

the capacitor can be reduced to 0.5µF and 0.15µF for 1mA. More

output capacitance needed for the 8-pin version at voltages below

5V since it runs the error amplifier at lower gain. At worst case

5µF or greater must be used for the condition of 250mA load at

1.23V output.

The SPX1129, unlike other low dropout regulators will remain

stable and in regulation with no load in addition to the internal

voltage divider. This feature is especially important in

application like CMOS RAM keep-alive. When setting the output

voltage of the SPX1129, a minimum load of 10mA is

recommended.

If there is more than 10 inches of wire between the input and the

AC filter capacitor or if a battery is used as the input then a 0.1µF

tantalum or aluminum electrolytic capacitor should be placed

from the input to the ground.

Instability can occur if there is stray capacitance to the SPX1129

feedback terminal (pin 7). This could cause more problems when

using a higher value of external resistors to set the output voltage.

This problem can be fixed by adding a 100pF capacitor between

output and feedback and increasing the output capacitor to at least

3.3µF.

ERROR DETECTION COMPARATOR OUTPUT

The Comparator produces a logic low output whenever the SPX1129

output falls out of regulation by more than around 5%. This is around

60mV offset divided by the 1.235 reference voltage. This trip level

remains 5% below normal regardless of the programmed output

voltage of the regulator. Figure 1 shows the timing diagram depicting

the ERROR signal and the regulator output voltage as the SPX1129

input is ramped up and down. The ERROR signal becomes low at

around 1.3V input, and goes high around 5V input (input voltage at

which Vout = 4.75). Since the SPX1129’s dropout voltage is load

dependent, the input voltage trip point (around 5V) will vary with the

load current. The output voltage trip point (approx. 4.75V) does not

vary with load.

The error comparator has an open-collector output, which requires an

external pull-up resistor. Depending on the system requirements the

resistor may be returned to 5V output or other supply voltage. In

determining the value of this resistor, note that the output is rated to

sink 400µA, this value adds to battery drain in a low battery

condition. Suggested values range from 100K to 1MΩ. If the output

is unused this resistor is not required.

PROGRAMMING THE OUTPUT VOLTAGE OF

SPX1129

The SPX1129 may be pin-strapped for 5V using its internal voltage

divider by tying Pin 1 (output) to Pin 2 (sense) and Pin 7 (feedback)

to Pin 6 (5V Tap).

SHUTDOWN

OUTPUT

VOLTAGE

4.75V

ERROR*

INPUT

VOLTAGE

+5.0V

+1.3V

+

+

* See Application Information.

Figure 1. ERROR Output Timing

VIN

GND

8

5

1

VOUT

SPX1129

3, 6, 7

2

ADJ

Figure 2. Adjustable Voltage Regulator

Rev. 10/25/00

Share Link: