Electronic Components Datasheet Search |
|
CS5124 Datasheet(PDF) 8 Page - ON Semiconductor |
|
CS5124 Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 11 page CS5124 http://onsemi.com 8 APPLICATION INFORMATION UVLO and Thermal Shutdown Interaction The UVLO pin and thermal shutdown circuit share the same internal comparator. During high temperature operation (TJ > 100°C) the UVLO pin will interact with the thermal shutdown circuit. This interaction increases the turn−on threshold (and hysteresis) of the UVLO circuit. If the UVLO pin shuts down the IC during high temperature operation, higher hysteresis (see hysteresis specification) might be required to enable the IC. BIAS Pin The bias pin can be used to control VCC as shown in the main application diagram in Figure 1. In order to provide adequate phase margin for the bias control loop, the pole created by the series pass transistor and the VCC bypass capacitor should be kept above 10 kHz. The frequency of this pole can be calculated by Formula (1). Pole Frequency + Transconductance of pass Transistor 2 p CV(CC) (1) The Line BIAS pin shows a significant change in the regulated VCC voltage when sinking large currents. This will show up as poor line regulation with a low value pull−up resistor. Typical regulated VCC vs BIAS pin sink current is shown in Figure 3. Figure 3. Regulated VCC vs. BIAS Sink Current 5.0 mΑ 10 mΑ 20 mΑ 50 mΑ 100 mΑ 200 mΑ Bias Current (IBIAS) 7.9 8.0 8.1 8.2 8.3 The BIAS pin and associated components form a high impedance node. Care should be taken during PCB layout to avoid connections that could couple noise into this node. To ensure adequate design margin between the regulated VCC and the Low VCC Lockout voltage, a guaranteed minimum differential between the two values is specified (see electrical characteristcs). Gate Drive Rail to rail gate driver operation can be obtained (up to 13.5 V) over a range of MOSFET input capacitance if the gate resistor value is kept low. Figure 5 shows the high gate drive level vs. the series gate resistance with VCC = 8.0 V driving an IRF220. Figure 4. Gate Drive vs. Gate Resistor Driving an IRF220 (VCC = 8.0 V) 0 Gate Resistor Value 8.5 0.3 0.5 2.5 5.0 8.0 7.5 7.0 6.5 6.0 11 A large negative dv/dt on the power MOSFET drain will couple current into the gate driver through the gate to drain capacitance. If this current is kept within absolute maximum ratings for the GATE pin it will not damage the IC. However if a high negative dv/dt coincides with the start of a PWM duty cycle, there will be small variations in oscillator frequency due to current in the controller substrate. If required, this can be avoided by choosing the transformer ratio and reset circuit so that a high dv/dt does not coincide with the start of a PWM cycle, or by clamping the negative voltage on the GATE pin with a Schottky diode First Current Sense Threshold During normal operation the peak primary current is controlled by the level of the VFB pin (as determined by the control loop) and the current sense network. Once the signal on the ISENSE pin exceeds the level determined by VFB pin the PWM cycle terminates. During high output currents the VFB pin will rise until it reaches the VFB clamp. The first current sense threshold determines the maximum signal allowed on the ISENSE pin before the PWM cycle is terminated. Under this condition the maximum peak current is determined by the VFB Clamp, the slope compensation ramp, the PWM comparator offset voltage and the PWM on time. The nominal first current threshold varies with on time and can be calculated from Formulas (2) and (3) below. 1st Threshold + 2.9 V * 170 mV ms TON 10 * 60 mV (2) When the output current is high enough for the ISENSE pin to exceed the first threshold, the PWM cycle terminates early and the converter begins to function more like a current source. The current sense network must be chosen so that the peak current during normal operation does not exceed the first current sense threshold. Second Current Sense Threshold The second threshold is intended to protect the converter from overheating by switching to a low duty cycle mode when there are abnormally high fast rise currents in the |
Similar Part No. - CS5124 |
|
Similar Description - CS5124 |
|
|
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 |