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HM1084 Datenblatt(PDF) 8 Page - Shenzhen Huazhimei Semiconductor Co., Ltd

Teile-Nr. HM1084
Beschreibung  1A low dropout linear regulator
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Hersteller  HMSEMI [Shenzhen Huazhimei Semiconductor Co., Ltd]
Homepage  http://www.hmsemi.com/
Logo HMSEMI - Shenzhen Huazhimei Semiconductor Co., Ltd

HM1084 Datenblatt(HTML) 8 Page - Shenzhen Huazhimei Semiconductor Co., Ltd

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Rev. 04
It is common practice to use several tantalum and ceramic capacitors in parallel to reduce this change in the output
voltage by reducing the overall ESR.
Output capacitance can be increased indefinitely to improve transient response and stability.
RIPPLE REJECTION
Ripple rejection is a function of the open loop gain within the feed-back loop (refer to Figure 1 and Figure 2). The
HM1084
exhibits 75dB of ripple rejection (typ.). When adjusted for voltages higher than VREF, the ripple rejection decreases as
function of adjustment gain: (1+R1/R2) or VO/VREF. Therefore a 5V adjustment decreases ripple rejection by a factor of
four (−12dB); Output ripple increases as adjustment voltage increases.
However, the adjustable version allows this degradation of ripple rejection to be compensated. The adjust terminal can
be bypassed to ground with a capacitor (CADJ). The impedance of the CADJ should be equal to or less than R1 at the
desired ripple frequency. This bypass capacitor prevents ripple from being amplified as the output voltage is increased.
LOAD REGULATION
The
HM1084 regulates the voltage that appears between its output and ground pins, or between its output and adjust pins.
In some cases, line resistances can introduce errors to the voltage across the load. To obtain the best load regulation, a
few precautions are needed.
Figure 3
shows a typical application using a fixed output regulator. Rt1 and Rt2 are the line resistances. VLOAD is less
than the VOUT by the sum of the voltage drops along the line resistances. In this case, the load regulation seen at the
RLOAD would be degraded from the data sheet specification. To improve this, the load should be tied directly to the output
terminal on the positive side and directly tied to the ground terminal on the negative side.
FIGURE 3. Typical Application using Fixed Output Regulator
When the adjustable regulator is used (Figure 4), the best performance is obtained with the positive side of the resistor
R1 tied directly to the output terminal of the regulator rather than near the load. This eliminates line drops from appearing
effectively in series with the reference and degrading regulation. For example, a 5V regulator with 0.05
resistance
between the regulator and load will have a load regulation due to line resistance of 0.05
x IL. If R1 (=125
) is
connected near the load the effective line resistance will be 0.05
(1 + R2/R1) or in this case, it is 4 times worse. In
addition, the ground side of the resistor R2 can be returned near the ground of the load to provide remote ground
sensing and improve load regulation.
FIGURE 4. Best Load Regulation using Adjustable Output Regulator
PROTECTION DIODES
Under normal operation, the
HM1084 regulator does not need any protection diode. With the adjustable device, the
internal resistance between the adjustment and output terminals limits the current. No diode is needed to divert the
current around the regulator even with a capacitor on the adjustment terminal. The adjust pin can take a transient signal
of ±25V with respect to the output voltage without damaging the device.
Shenzhen H&M Semiconductor Co.Ltd
http://www.hmsemi.com


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