AMSCM 5A Low Dropout Voltage Regulator FEATURES. Three Terminal Adjustable or Fixed V, V and V Output Current of 5A Operates Down to. the end of the datasheet. Typical Application. 1. An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in. The AIC is a low dropout three terminal regulator with 5A output current capability. The output voltage is adjustable with the use of a resistor divider or fixed.
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It has the same pin-out as National Semiconductor’s industry standard LM The LM is available in an adjustable version, which can set the output voltage with only two external resistors.
It is also available in three fixed voltages: The fixed versions intergrate the adjust resistors. C Line Regulation 0. C 25V Output Section ? Limits appearing in Boldface type apply over the entire junction temperature range for operation.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.
Power dissipation is kept in a safe range by current limiting circuitry. Refer to Overload Recovery in Application Notes. The maximum power dissipation is a function of TJ max ,? All numbers apply for packages soldered directly into a PC board. Refer to Thermal Considerations in the Application Notes. For testing purposes, ESD was applied using human body model, 1.
Typical Values represent the most likely parametric norm. All limits are guaranteed by testing or statistical analysis. Note that 30W power dissipation for the LM is only achievable over a limited range of input-to-output voltage.
Load and line regulation are measured at constant junction temperature, and are guaranteed up to the maximum power dissipation of 30W. Dropout voltage is specified over the full output current range of the device. The minimum output current required to maintain regulation. In order for stable operation, the loop must maintain negative feedback. The LM requires a certain amount series resistance with capacitive loads.
This series resistance introduces a zero within the loop to increase phase margin and thus increase stability. The equivalent series resistance ESR of solid tantalum or aluminum electrolytic capacitors is used to provide the appropriate zero approximately kHz. General Figure 1 shows a basic functional diagram for the LMAdj excluding protection circuitry. The topology is basically that of the LM except for the pass transistor. This results in a lower dropout voltage. The structure of the pass transistor is also known as a quasi LDO.
The LM is guaranteed to provide a minimum dropout voltage 1. The Aluminum electrolytic are less expensive than tantalums, but their ESR varies exponentially at cold temperatures; therefore requiring close examination when choosing the desired transient response over temperature.
Tantalums are a convenient choice because their ESR varies less than 2: These values will assure stability for the majority of applications. The adjustable versions allows an additional capacitor to be used at the ADJ pin to increase ripple rejection. If this is done the output capacitor should be increased to 22uF for tantalums or to uF for aluminum. Capacitors other than tantalum or aluminum can be used at the adjust pin and the input pin. A 10uF capacitor is a reasonable value at the input.
See Ripple Rejection section regarding the value for the adjust pin capacitor. It is desirable to have large output capacitance for applications that entail large changes in load current microprocessors for example. The higher the capacitance, the larger the available charge per demand.
It is also desirable to provide low ESR to reduce the change in output voltage: As shown in figure 2, this voltage is applied across resistor R1 to generate a constant current I1.
This constant current then flows through R2. The resulting voltage drop across R2 adds to the reference voltage to sets the desired output voltage. The current IADJ from the adjustment terminal introduces an output error.
But since it is small uA maxit becomes negligible when R1 is in the Ohm range. For fixed voltage devices, R1 and R2 are integrated inside the devices. I x ESR 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 LM exhibits 75dB of ripple rejection typ.
When adjusted for voltages higher than VREF, the ripple rejection decreases as function of adjustment gain: Therefore a 5V adjustment decreases ripple rejection by a factor of four dB ; 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.
This bypass capacitor prevents ripple from being amplified as the output voltage is increased. 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. Basic Adjustable Regulator 7 www. The discharge current depends on the value of the capacitor, the output voltage of the regulator, and rate of decrease of VIN. In the LM regulator, the internal diode between the output and input pins can withstand microsecond surge currents of 10A to 20A. In this case, an external diode is recommended between the output and input pins to protect the regulator, shown in Figure 5.
Continued than the VOUT by the sum of the voltage drops along the line resistances.
CM Datasheet, PDF – Alldatasheet
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.
Typical Application using Fixed Output Regulator When the adjustable regulator is used Figure 4the dztasheet 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.
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. Regulator with Protection Diode Overload Recovery Overload recovery refers to regulator’s ability to recover from a short circuited output. A key factor in the recovery process is the current limiting used to protect the output from drawing too much power.
The current limiting circuit reduces the output current as the input to output differential increases.
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Refer to short circuit curve in the curve section. During normal start-up, the input to output differential is small since the output follows the input. But, if the output is shorted, then the recovery involves a large input to output differential.
Sometimes during this condition darasheet current limiting circuit is slow in recovering. If the limited current is too low to develop a voltage at the output, 1804cm voltage will stabilize at a lower level.
Under these conditions it may be necessary to recycle the power of the regulator in order to get the smaller differential voltage and thus 1084cn start up conditions. Refer to curve section for the short circuit current vs. Thermal Considerations ICs heats up when in operation, and power consumption is one factor in how 104cm it gets. The other factor is how well the heat is dissipated. Heat dissipation is predictable by knowing the thermal resistance between the IC and ambient?
The higher the thermal resistance, the hotter the IC. 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 datqsheet take a transient signal of? In order to get the total resistance to ambient? JAtwo other thermal resistance must be added, one for case to heat-sink? CH and one for heatsink to ambient?
The junction temperature can be predicted as follows: Device power consumption is calculated datasbeet follows: HA max should also be calculated twice as follows: Once the devices power is determined, the maximum allowable?
JA max is calculated as: The Electrical Datzsheet table shows the junction to case thermal resistances for each of these sections, while the maximum junction temperatures TJ max for each section is listed in the Absolute Maximum section of the datasheet. TJ max is ?