U6084B

Features • • • • • Pulse-width Modulation up to 2-kHz Clock Frequency Protection Against Short-circuit, Load-dump Overvoltage and Reverse VS Duty Cycle 0% to 100% Continuously Output Stage for Power MOSFET Interference and Damage Protection According to VDE 0839 and ISO/TR 7637/1 • Charge-pump Noise Suppressed • Ground-wire Breakage Protection 1. Description The U6084B is a PWM-IC with bipolar technology designed for the control of an N-channel power MOSFET used as a high-side switch. The IC is ideal for use in the brightness control (dimming) of lamps such as in dashboard applications. For constant brightness, the preselected duty cycle can be reduced automatically as a function of the supply voltage. PWM Power Control with Automatic Duty-cycle Reduction U6084B Figure 1-1. Block Diagram with External Circuit C5 16 9 Short circuit latch monitoring 5 RC oscillator 6 Charge 13 pump PWM Logic 3 Control input Output 14 C3 47 nF 11 Current monitoring + short circuit detection 12 Rsh VBatt VS C1 47 kΩ C2 Duty cycle range 0-100% Duty cycle reduction 4 Voltage monitoring 1 Enable/ disable 2 150 Ω R3 Ground . Rev. 4677C–AUTO–09/05 2. Pin Configuration Figure 2-1. Pinning SO16 GND EN/DIS VI REDUCT NC OSC NC NC 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 VS NC OUTPUT 2 VS SENSE DELAY NC LATCH Table 2-1. Pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Pin Description Symbol GND EN/DIS VI REDUCT NC OSC NC NC LATCH NC DELAY SENSE 2VS OUTPUT NC VS Function IC ground Enable/disable Control input (duty cycle) Duty cycle reduction Attenuation Oscillator Not connected Not connected Status short-circuit latch Not connected Short-circuit protection delay Current sensing Voltage doubler Output Not connected Supply voltage VS 2 U6084B 4677C–AUTO–09/05 U6084B 3. Functional Description 3.1 3.1.1 Pin1 – GND Ground-wire Breakage To protect the FET in case of ground-wire breakage, a 820-kΩ resistor between gate and source is recommended to provide proper switch-off conditions. 3.2 Pin 2 – Enable/Disable The dimmer can be switched on or off with pin 2, independently of the set duty cycle. Table 3-1. V2 > approximately 0.7V or open < 0.7V or connected to pin 1 Pin 2 Function Function Disable Enable 3.3 Pin 3 – Control Input The pulse width is controlled by means of an external potentiometer (47 kΩ). The characteristic (angle of rotation/duty cycle) is linear. The duty cycle be varied from 0% to 100%. It is possible to further restrict the duty cycle with resistors R1 and R2 (Figure 7-1 on page 9). Pin 3 is protected against short-circuit to VBatt and ground GND (VBatt ≤16.5V). 3.4 Pin 4 – Duty Cycle Reduction With pin 4 connected according to Figure 7-1 on page 9, the set duty cycle is reduced to VBatt ≈ 12.5V. This causes a power reduction in the FET and in the lamps. In addition, the brightness of the lamps is largely independent of the supply voltage range, VBatt = 12.5V to 16V. 3.4.1 Output Slope Control The rise and fall time (tr, tf) of the lamp voltage can be limited to reduce radio interference. This is done with an integrator which controls a power MOSFET as source follower. The slope time is controlled by an external capacitor C4 and the oscillator current (Figure 7-1 on page 9). Calculation: C4 t f = t r = V Batt × -------I osc With VBatt = 12V, C4 = 470 pF and Iosc = 40 µA, the controlled slope is 470 pF t f = t r = 12V × ----------------- × 141 µs 40 µA 3.5 Pin 5 – Attenuation Capacitor C4 connected to pin 5 damps oscillation tendencies. 3 4677C–AUTO–09/05 3.6 Pin 6 – Oscillator The oscillator determines the frequency of the output voltage. This is defined by an external capacitor, C2. It is charged with a constant current, I, until the upper switching threshold is reached. A second current source is then activated which taps a double current, 2 × I, from the charging current. The capacitor, C2, is thus discharged by the current, I, until the lower switching threshold is reached. The second source is then switched off again and the procedure starts once more. 3.6.1 Example for Oscillator Frequency Calculation V T100 = V S × α1 = ( V Batt – I S × R 3 ) × α1 V T