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NCV8570MN300R2G Datasheet(PDF) 9 Page - ON Semiconductor |
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NCV8570MN300R2G Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 12 page NCV8570 http://onsemi.com 9 APPLICATION INFORMATION General The NCV8570 is a 200 mA (current limited) linear regulator with a logic input for on/off control for the high speed turn−off output voltage. Access to the major contributor of noise within the integrated circuit is provided as the focus for noise reduction within the linear regulator system. Power Up/Down During power up, the NCV8570 maintains a high impedance output (Vout) until sufficient voltage is present on Vin to power the internal bandgap reference voltage. When sufficient voltage is supplied (approx 1.2 V), Vout will start to turn on (assume CE shorted to Vin), linearly increasing until the output regulation voltage has been reached. Active discharge circuitry has been implemented to insure a fast turn off time. Then CE goes low, the active discharge transistor turns on creating a fast discharge of the output voltage. Power to drive this circuitry is drawn from the output node. This is to maintain the lowest quiescent current when in the sleep mode (VCE = 0.4 V). This circuitry subsequently turns off when the output voltage discharges. CE (chip enable) The enable function is controller by the logic pin CE. The voltage threshold of this pin is set between 0.4 V and 1.2 V. A voltage lower than 0.4 V guarantees the device is off. A voltage higher than 1.2 V guarantees the device is on. The NCV8570 enters a sleep mode when in the off state drawing less than 1 mA of quiescent current. The device can be used as a simple regulator without use of the chip enable feature by tying the CE pin to the Vin pin. Current Limit Output Current is internally limited within the IC to a minimum of 200 mA. The design is set to a higher value to allow for variation in processing and the temperature coefficient of the parameter. The NCV8570 will source this amount of current measured with a voltage 100 mV lower than the typical operating output voltage. The specification for short circuit current limit (@ Vout = 0 V) is specified at 320 mA (typ). There is no additional circuitry to lower the current limit at low output voltages. This number is provided for informational purposes only. Output Capacitor The NCV8570 has been designed to work with low ESR ceramic capacitors. There is no ESR lower limit for stability for the recommended 1 mF output capacitor. Stable region for Output capacitor ESR vs Output Current is shown in Figure 23. Typical characteristics were measured with Murata ceramic capacitors. GRM219R71E105K (1 mF, 25 V, X7R, 0805) and GRM21BR71A106K (10 mF, 10 V, X7R, 0805). Output Noise The main contributor for noise present on the output pin Vout is the reference voltage node. This is because any noise which is generated at this node will be subsequently amplified through the error amplifier and the PMOS pass device. Access to the reference voltage node is supplied directly through the Cnoise pin. Noise can be reduced from a typical value of 20 mVrms by using 10 nF to 15 mVrms by using a 100 nF from the Cnoise pin to ground. A bypass capacitor is recommended for good noise performance and better load transient response. Thermal Shutdown When the die temperature exceeds the Thermal Shutdown threshold, a Thermal Shutdown (TSD) event is detected and the output (Vout) is turned off. There is no effect from the active discharge circuitry. The IC will remain in this state until the die temperature moves below the shutdown threshold (150 °C typical) minus the hysteresis factor (20°C typical). This feature provides protection from a catastrophic device failure due to accidental overheating. It is not intended to be used as a substitute for proper heat sinking. The maximum device power dissipation can be calculated by: PD + TJ * TA RqJA Thermal resistance value versus copper area and package is shown in Figure 24. Figure 24. RqJA vs. PCB Copper Area PCB COPPER AREA (mm2) 700 600 500 400 300 200 100 0 80 130 180 230 280 330 380 TSOP−5 (1 oz) TSOP−5 (2 oz) DFN6 2x2.2 (1 oz) DFN6 2x2.2 (2 oz) (TSOP−5 for comparison only) |
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