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HV9608 Datasheet(PDF) 5 Page - Supertex, Inc |
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HV9608 Datasheet(HTML) 5 Page - Supertex, Inc |
5 / 6 page HV9608 5 A122104 Functional Block Diagram High Voltage startup regulator VIN REF UVLO Bandgap reference + - 1.135V RT Oscillator SQ R VS + - 1.135V pwm Comp + eAmp 1.135V 0.6V + - GATE VDD driver FB Delay Logic AGATE DT1 DT2 100ns blanking CS + - 3.85V Ι Ι UVLO SS GND + - 0.6V + - ramp SC R POR + - 1.135V 5.45V Functional Description HIGH VOLTAGE REGULATOR When DC voltage from 12 to 250V is applied to the VIN pin, an internal high voltage linear regulator provides a regulated output voltage of 9.3V at the VDD pin. This voltage can be used to start the DC/DC converter. Applying external voltage to the VDD pin that is higher than its output voltage will disable the regulator. Therefore, the VIN pin will draw negligible current once the DC/DC converter has started, and a “bootstrap” voltage has developed at the VDD pin. Alternatively, the high voltage regulator can continuously supply bias current up to 20mA powering the gate driver and all internal circuits of HV9608. The need for a bootstrap power supply would be eliminated in this case. However, caution must be taken to maintain the HV9608 within its package power dissipation limits. The output of the linear regulator is equipped with an under voltage protection comparator that disables all internal circuits when the voltage at the VDD pin falls below 7.62V. Hysteresis of 0.76V is provided. INPUT UNDER VOLTAGE LOCKOUT (UVLO) The HV9608 provides a programmable under voltage protection input (UVLO pin) that allows independent setting of the turn-on and the turn-off limits for the input voltage of the DC/DC converter. When the voltage applied to the UVLO pin exceeds 1.135V, the gate driver and the reference voltage at the VREF pin are enabled, and the DC/DC converter starts switching. At the same time, a current of 14µA is sourced from the UVLO pin. This current sets the hysteresis that can be calculated in accordance with the following equation: 12 12 14 UVLO R R VA R R µ ⋅ ∆= ⋅ + , where R1 and R2 are the input voltage divider resistors. OSCILLATOR FREQUENCY The switching frequency of the HV9608 can be programmed using a single resistor connected to the RT pin: [] [] 9 1 300 10 OSC T T FHz R CF − ⎛⎞ −⋅ ⎜⎟ ⎜⎟ ⎝⎠ = SOFT START As soon as the voltage at the VDD pin exceeds the turn-on threshold, a 7µA current is sourced from the SS pin into an external soft-start capacitor CSS. As the voltage across CSS ramps up linearly, the output of the error amplifier (COMP) gradually increases until regulation of the output voltage is achieved. Sizing CSS programs the time duration of the soft start mode. When CSS is sized properly, no overshoot of the output voltage or excessive input inrush current will occur. When the voltage at the VDD pin falls below the under voltage protection threshold, CSS is rapidly discharged to zero. |
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