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NCP3064PG Datasheet(PDF) 8 Page - ON Semiconductor |
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NCP3064PG Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 20 page NCP3064, NCP3064B, NCV3064 http://onsemi.com 8 Peak Current Sense Comparator With a voltage ripple gated converter operating under normal conditions, output switch conduction is initiated by the Voltage Feedback comparator and terminated by the oscillator. Abnormal operating conditions occur when the converter output is overloaded or when feedback voltage sensing is lost. Under these conditions, the Ipk Current Sense comparator will protect the Darlington output Switch. The switch current is converted to a voltage by inserting a fractional W resistor, RSC, in series with VCC and the Darlington output switch. The voltage drop across RSC is monitored by the Current Sense comparator. If the voltage drop exceeds 200 mV with respect to VCC, the comparator will set the latch and terminate output switch conduction on a cycle−by−cycle basis. This Comparator/Latch configuration ensures that the Output Switch has only a single on−time during a given oscillator cycle. Real Vturn−off on Rs Resistor t_delay I1 Io di/dt slope I through the Darlington Switch Vipk(sense) Figure 14. Current Sense Waveform The VIPK(Sense) Current Limit Sense Voltage threshold is specified at static conditions. In dynamic operation the sensed current turn−off value depends on comparator response time and di/dt current slope. Real Vturn−off on Rsc resistor Vturn_off = Vipk(sense) + Rs*(tdelay*di/dt) Typical Ipk comparator response time tdelay is 350 ns. The di/dt current slope is growing with voltage difference on the inductor pins and with decreasing inductor value. It is recommended to check the real max peak current in the application at worst conditions to be sure that the maximum peak current will never get over the 1.5 A Darlington Switch Current maximum rating. Thermal Shutdown Internal thermal shutdown circuitry is provided to protect the IC in the event that the maximum junction temperature is exceeded. When activated, typically at 160 °C, the Output Switch is disabled. The temperature sensing circuit is designed with 10 °C hysteresis. The Switch is enabled again when the chip temperature decreases to at least 150 °C threshold. This feature is provided to prevent catastrophic failures from accidental device overheating. It is not intended to be used as a replacement for proper heat−sinking. Output Switch The output switch is designed in a Darlington configuration. This allows the application designer to operate at all conditions at high switching speed and low voltage drop. The Darlington Output Switch is designed to switch a maximum of 40 V collector to emitter voltage and current up to 1.5 A ON/OFF Function The ON/OFF function disables switching and puts the part into a low power consumption mode. A PWM signal up to 1 kHz can be used to pulse the ON/OFF and control the output. Pulling this pin below the threshold voltage (~1.4 V) or leaving it open turns the regulator off and has a standby current <100 mA. Pulling this pin above 1.4 V (up to 25 V max) allows the regulator to run in normal operation. If the ON/OFF feature is not needed, the ON/OFF pin can be connected to the input voltage VCC, provided that this voltage does not exceed 25 V. |
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