Electronic Components Datasheet Search |
|
CS5233-3GDFR8 Datasheet(PDF) 8 Page - ON Semiconductor |
|
CS5233-3GDFR8 Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 12 page CS5233−3 http://onsemi.com 8 respond. One of the consequences of providing this current is an instantaneous voltage drop at VIN due to capacitor ESR. The magnitude of the voltage change is again the product of the current change and the capacitor ESR. It is very important to consider the maximum current step that can exist in the system. If the change in current is large enough, it is possible that the instantaneous voltage drop on VIN will exceed the VIN threshold hysteresis, and the IC will enter a mode of operation resembling an oscillation. As the part turns on, the output current IOUT will increase, reaching current limit during initial charging. Increasing IOUT results in a drop at VIN such that the shutdown threshold is reached. The part will turn off, and the load current will decrease. As IOUT decreases, VIN will rise and the part will turn on, starting the cycle all over again. This oscillatory operation is most likely at initial start−up when the output capacitance is not charged, and in cases where the ramp−up of the VIN supply is slow. It may also occur during the power transition when the linear regulator turns on and the PFET turns off. A 20 ms delay exists between turn−on of the regulator and the AuxDrv pin pulling the gate of the PFET high. This delay prevents “chatter” during the power transitions. If required, using a few capacitors in parallel to increase the bulk charge storage and reduce the ESR should give better performance than using a single input capacitor. Short, straight connections between the power supply and VIN lead along with careful layout of the PC board ground plane will reduce parasitic inductance effects. Wide VIN and VOUT traces will reduce resistive voltage drops. Choosing the PFET Switch The choice of the external PFET switch is based on two main considerations. First, the PFET should have a very low turn−on threshold. Choosing a switch transistor with VGS(ON) ≈ 1.0 V will ensure the PFET will be fully enhanced with only 3.3 V of gate drive voltage. Second, the switch transistor should be chosen to have a low RDS(ON) to minimize the voltage drop due to current flow in the switch. The formula for calculating the maximum allowable on−resistance is RDS(ON)MAX + VAUX(MIN) * VOUT(MIN) 1.5 IOUT(MAX) VAUX(MIN) is the minimum value of the auxiliary supply voltage, VOUT(MIN) is the minimum allowable output voltage, IOUT(MAX) is the maximum output current and 1.5 is a “fudge factor” to account for increases in RDS(ON) due to temperature. Output Voltage Sensing It is not possible to remotely sense the output voltage of the C5233−3 since the feedback path to the error amplifier is not externally available. It is important to minimize voltage drops due to metal resistance of high current PC board traces. Such voltage drops can occur in both the supply traces and the return traces. The following board layout practices will help to minimize output voltage errors: • Always place the linear regulator as close to both load and output capacitors as possible. • Always use the widest possible traces to connect the linear regulator to the capacitor network and to the load. • Connect the load to ground through the widest possible traces. • Connect the IC ground to the load ground trace at the point where it connects to the load. Current Limit The CS5233−3 has internal current limit protection. Output current is limited to a typical value of 3.0 A for the D2PAK using VIN and 800 mA using VSB, even under output short circuit conditions. If the load current drain exceeds the current limit value, the output voltage will be pulled down and will result in an out of regulation condition. Thermal Shutdown The CS5233−3 has internal temperature monitoring circuitry. The output is disabled if junction temperature of the IC reaches 180 °C. Thermal hysteresis is typically 25°C and allows the IC to recover from a thermal fault without the need for an external reset signal. The monitoring circuitry is located near the composite PNP−NPN output transistor, since this transistor is responsible for most of the on−chip power dissipation. The combination of current limit and thermal shutdown will protect the IC from nearly any fault condition. Reverse Current Protection During normal system operation, the auxiliary drive circuitry will maintain voltage on the VOUT pin. IC reliability and system efficiency are improved by limiting the amount of reverse current that flows from VOUT to ground and from VOUT to VIN. Current flows from VOUT to ground through the feedback resistor divider that sets up the output voltage, typically 400 mA. Current flow from VOUT to VIN will be limited to leakage current after the IC shuts down. On−chip RC time constants are such that the output transistor should be turned off well before VIN drops below the VOUT voltage. Calculating Power Dissipation and Heatsink Requirements Most linear regulators operate under conditions that result in high on−chip power dissipation. This results in high junction temperatures. Since the IC has a thermal shutdown feature, ensuring the regulator will operate correctly under normal conditions is an important design consideration. Some heatsinking will usually be required. Thermal characteristics of an IC depend on four parameters: ambient temperature (TA in °C), power dissipation (PD in watts), thermal resistance from the die to |
Similar Part No. - CS5233-3GDFR8 |
|
Similar Description - CS5233-3GDFR8 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |