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參數(shù)資料
| 型號： | 935269469115 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 固定正電壓單路輸出LDO穩(wěn)壓器 |
| 英文描述： | 4.8 V FIXED POSITIVE LDO REGULATOR, 0.2 V DROPOUT, PDSO5 |
| 封裝： | PLASTIC, MO-178, SOT-23, SOT-25, SO-5 |
| 文件頁數(shù)： | 17/17頁 |
| 文件大?。?/td> | 212K |
| 代理商： | 935269469115 |
Philips Semiconductors
Product data
SA57001-XX
Microminiature, low power consumption,
low dropout regulator
2003 Mar 20
9
TECHNICAL DESCRIPTION
The SA57001 is a family of series regulators incorporating a
bandgap reference, two feedback amplifiers, a thermal shutdown
circuit, and an output current limiting circuit. Both feedback
amplifiers are referenced to the bandgap reference. See the device
diagram shown in Figure 22.
A PNP transistor in the device’s output serves as the series pass
element. The output PNP pass transistor incorporates a dual
collector.
The first feedback amplifier monitors the first collector’s output
voltage through the use of a voltage divider network fed directly from
the output. The second collector produces a small current that is
proportional to the output current. The proportional current flows
through a resistor, generating a second feedback voltage that is
proportional to the output current. This voltage is fed to the second
feedback amplifier to limit the output current to a safe operating
level.
Both feedback amplifiers act on the same control node, to control
the PNP pass transistor’s conduction. This dual path output
monitoring maintains a constant output voltage while also limiting
the output current.
Stability factors: Capacitance and ESR
The operating stability of linear regulators is determined by start-up
delay, transient response to load currents, and stability of the
feedback loop. The SA57001 has a fast transient loop response,
with no built-in delay.
Capacitors play an important part in compensating the regulator’s
output. A 4.7
F aluminum electrolytic capacitor is recommended for
most applications, because they provide good performance with
minimal cost. A tantalum capacitor can also be used. Tantalum
capacitors are smaller than electrolytic capacitors of the same
capacitance value. Tantalum capacitors also are not prone to
dry-out. The electrolyte used in electrolytic capacitors tends to dry
out with time, degrading the performance. Avoid using extremely low
ESR film or ceramic capacitors to avoid instability problems. See
Figure 9, ‘ESR stability versus output current’.
Keep in mind that the output capacitor tries to supply any
instantaneous increase in load current from its stored energy. Using
higher values of capacitance will enhance transient load performance
as well as stability. Lowering the ESR of the capacitors will also
improve the transient response to load current changes, but it will
decrease stability.
Noise reduction
The noise reduction pin of the device is connected to the internal
reference voltage node. Bypassing this pin to ground with a
capacitor (0.01
F typical) will reduce the output voltage noise for
demanding applications. This also improves the AC performance by
increasing ripple rejection.
In addition, bypassing the input pin to ground with a capacitor
(0.1
F typical) will suppress input ripple form the power source.
Thermal overload protection
When the junction temperature reaches approximately 150
°C, the
thermal sensor signals the shutdown logic to turn off the pass
transistor. After the junction temperature has cooled to below the
thermal threshold, plus the hysteresis, the sensor signals the
shutdown logic to turn the pass transistor on again. This will create a
pulsed output during lengthy thermal overloads.
NOTE: Thermal overload protection is to protect the device during
fault conditions. Do not exceed the maximum junction-temperature
rating of Tj = +150 °C during continuous operation.
SL01419
VIN
NOISE
VOUT
4
1
3
5
GND
2
300 k
400 k
THERMAL
SHUTDOWN
ON/OFF
Figure 22. Functional diagram.
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