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U6084B
PWM Power Control with Automatic Duty-Cycle Reduction
Description
The U6084B is a PWM-IC in bipolar technology designed for the control of an N-channel power MOSFET used as a high-side switch. The IC is ideal for the 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.
Features
D Pulse-width modulation up to 2 kHz clock frequency D Protection against short overvoltage and reverse VS circuit, load-dump D Interference and damage protection according to VDE 0839 and ISO/TR 7637/1. D Charge-pump noise suppressed D Ground-wire breakage protection
D Duty cycle 0 to 100 % continuously D Output stage for power MOSFET
Block Diagram
C5 VS 16 9 Short circuit latch monitoring 5 6 C1 47 kW 3 C2 Control input RC oscillator PWM Logic Output 14 Charge pump 13 C3 47 nF 11 Current monitoring + short circuit detection 12 Rsh VBatt
Duty cycle range 0-100%
Duty cycle reduction 4 C6
Voltage monitoring 1
Enable/ disable 2
95 9751
150W
R3 Ground
Figure 1. Block diagram with external circuit
Ordering Information
Extended Type Number U6084B-FP Package SO16 Remarks
Rev. A3, 11-Apr-01
1 (9)
U6084B
Pin Description
Pin GND En / Dis VI Reduct 1 2 3 4 16 15 14 13 12 11 10 9
95 9754
Symbol GND En / Dis VI Reduct NC Osc NC NC Latch NC Delay Sense 2VS Output NC VS IC ground
Function 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
VS NC Output 2 VS Sense Delay NC Latch
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Attenuation 5 Osc NC NC 6 7 8
Functional Description
Pin1, GND
Ground-Wire Breakage To protect the FET in the case of ground-wire breakage, a 820-kW resistor between gate and source is recommended to provide proper switch-off conditions.
Pin 4, Duty Cycle Reduction
With Pin 4 connected according to figure 2, the set duty cycle is reduced as from VBatt 12.5 V. 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 = 12.5 to 16 V. 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 (see figure 2). Calculation: C4 I osc With VBatt = 12 V, C4 = 470 pF and Iosc = 40 m A,we thus obtain a controlled slope of t f + t r + V Batt t f + t r + 12 V 470 pF + 141 ms 40 mA
Pin 2, Enable/Disable
The dimmer can be switched on or off with pin 2 independently of the set duty cycle. V2 Function Approx. > 0.7 V or open Disable < 0.7 V or connected to Pin 1 Enable
Pin 3, Control Input
The pulse width is controlled by means of an external potentiometer (47 kW). The characteristic (angle of rotation/duty cycle) is linear. The duty cycle can be varied from 0 to 100%. It is possible to further restrict the duty cycle with the resistors R1 and R2 (see figure 2). Pin 3 is protected against short-circuit to VBatt and ground GND (VBatt x 16.5 V).
Pin 5, Attenuation
Capacitor C4 connected to Pin 5 damps oscillation tendencies.
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U6084B
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. Example for Oscillator Frequency Calculation V T100 + VS V T|100 + VS V TL + VS where V T100 + High switching threshold (100% duty cycle)
V Tt100 + High switching threshold (t 100% duty cycle)
f+
2
(V Tt100 * V TL)
Iosc C2 ) 4
V Batt
C4
where
+ 2
C4 = 470 pF
7.6 V * 3.2 V 40 mA 22 nF ) 4 12 V 470 pF
+ 185 Hz A selection of different values of C2 and C4 provides a range of oscillator frequencies from 10 to 2000 Hz.
a1 + (V Batt * I S a2 + (V Batt * I S a3 + (V Batt * I S
R 3) R 3) R 3)
a1 a2 a3
Pins 7, 8, 10 and 15
Not connected.
Pin 9, Status Short Circuit Latch
The status of the short-circuit latch can be monitored via Pin 9 (open collector output). Pin 9 L H Function Short-circuit detected Not short-circuit detected
V TL + Low switching threshold a1, a2 and a3 are fixed values. The above mentioned threshold voltages are calculated for the following values given in the data sheet. VBatt = 12 V, IS = 4 mA, R3 = 150 W , a1 = 0.7, a2 = 0.67 and a3 = 0.28. V T100 + (12 V * 4 mA V Tt100 + 11.4 V V TL + 11.4 V 150 W ) 0.7 [ 8 V
Pins 11 and 12, Short-Circuit Protection and Current Sensing
1. Short-Circuit Detection and Time Delay, td The lamp current is monitored by means of an external shunt resistor. If the lamp current exceeds the threshold for the short-circuit detection circuit (VT2 90 mV), the duty cycle is switched over to 100% and the capacitor C5 is charged by a current source of 20 m A (Ich - Idis). The external FET is switched off after the cut-off threshold (VT11) is reached. Renewed switching on the FET is possible only after a power-on reset. The current source, Idis, ensures that the capacitor C5 is not charged by parasitic currents. The capacitor C5 is discharged by Idis to typ. 0.7 V. Time delay, td, is as follows: t d + C5 (VT11 * 0.7 V) (Ich * I dis)
0.67 + 7.6 V 0.28 + 3.2 V
For a duty cycle of 100%, the oscillator frequency, f, is as follows: f+ 2 I osc (V T100 * V TL) C2 , where C 2 + 22 nF and I osc + 40 mA
Therefore: f+ 2 40 mA (8 V * 3.2 V) 22 nF + 189 Hz
With C5 = 330 nF and VBatt = 12 V, we have t d + 330 nF + 150 ms. (9.8 V * 0.7 V) 20 mA
For a duty cycle of less than 100%, the oscillator frequency, f, is as follows:
Rev. A3, 11-Apr-01
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U6084B
2. Current Limitation The lamp current is limited by a control amplifier that protects the external power transistor. The voltage drop across an external shunt resistor acts as the measured variable. Current limitation takes place for a voltage drop of VT1 100 mV. Owing to the difference VT1-VT2 10 mV, current limitation occurs only when the short-circuit detection circuit has responded. After a power-on reset, the output is inactive for half an oscillator cycle. During this time , the supply voltage capacitor can be charged so that current limitation is guaranteed in the event of a short circuit when the IC is switched on for the first time.
Pin 16, Supply Voltage, Vs or VBatt
Undervoltage Detection: In the event of voltages of approx. VBatt < 5.0 V, the external FET is switched off and the latch for short-circuit detection is reset. A hysteresis ensures that the FET is switched on again at approximately VBatt 5.4 V. Overvoltage Detection Stage 1 If overvoltages of VBatt > 20 V (typ.) occur, the external transistor is switched off and switched on again at VBatt < 18.5 V (hysteresis). Stage 2 If VBatt > 28.5 V (typ.), the voltage limitation of the IC is reduced from 26 V to 20 V. The gate of the external transistor remains at the potential of the IC ground, thus producing voltage sharing between FET and lamps in the event of overvoltage pulses (e.g., load-dump). The shortcircuit protection is not in operation. At VBatt < 23 V, the overvoltage detection stage 2 is switched off.
Pins 13 and 14, Charge Pump and Output
Pin 14 (output) is suitable for controlling a power MOSFET. During the active integration phase, the supply current of the operational amplifier is mainly supplied by the capacitor C3 (bootstrapping). Additionally, a trickle charge is generated by an integrated oscillator (f13 400 kHz) and a voltage doubler circuit. This permits a gate voltage supply at a duty cycle of 100%.
Absolute Maximum Ratings
Parameters Junction temperature Ambient temperature range Storage temperature range Symbol Tj Tamb Tstg Value 150 -40 to +110 -55 to +125 Unit C C C
Thermal Resistance
Parameters Junction ambient Symbol RthJA Value 120 Unit K/W
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Rev. A3, 11-Apr-01
U6084B
Electrical Characteristics
Tamb = -40 to +110C, VBatt = 9 to 16.5 V, (basic function is guaranteed between 6.0 V to 9.0 V) reference point ground, unless otherwise specified (see figure 1). All other values refer to Pin GND (Pin 1). Parameters Current consumption Supply voltage Stabilized voltage Battery undervoltage detection Stage 1: Stage 2: Stabilized voltage Short-circuit protection Short-circuit current limitation Short-circuit detection VT1 = VS - V12 VT2 = VS - V12 Test Conditions / Pins Pin 16 Overvoltage detection, stage 1 IS = 10 mA - on - off Pin 2 VBatt VBatt Pin 16 Pin 12 VT1 VT2
VT1 - VT2
Symbol IS VBatt VS VBatt
Min.
Typ.
Max. 6.8 25
Unit mA V V V
Pin 16
24.5 4.4 4.8 18.3 16.7 25.5 19.5 18.5 85 75 3 9.5 5.0 5.4 20.0 18.5 28.5 23.0 20.0 100 90 10 9.8 23 3 13 20 150 2 VS 280 26 (VS+14) 0.35 400 27.5 (VS+15) 0.70
27.0 5.6 6.0 21.7 20.3 32.5 26.5 21.5 120 105 30 10.1
Battery overvoltage detection - on - off - on - off IS = 30 mA
V V V mV mV mV V mA mA
VZ
Delay timer short circuit detection Switched off threshold Charge current Dicharge current Capacitance current Saturation voltage Voltage doubler Voltage Oscillator frequency Internal voltage limitag tion i Gate output Voltage g Low level VBatt = 16.5 V, Tamb = 110 C, R3 = 150 W High level, duty cycle 100% *) Reference point is battery ground. I13 = 5 mA (whichever is lower) Duty cycle 100% I5 = Ich - Idis Output short-circuit latch I9 = 100 mA VT11 = VS - V11
Pin 11 VT11 Ich Idis I5 Pin 9 Vsat Pin 13 V13 f13 V13 V13 Pin 14 V14 0.95 1.5 *) V14 V13 V 520 30.0 (VS+16) kHz V 350 mV
27
mA
Rev. A3, 11-Apr-01
5 (9)
U6084B
Electrical Characteristics (continued)
Tamb = -40 to +110C, VBatt = 9 to 16.5 V, (basic function is guaranteed between 6.0 V to 9.0 V) reference point ground, unless otherwise specified (see figure 1). All other values refer to Pin GND (Pin 1). Parameters Current Enable/ Disable Current Duty cycle reduction Z-voltage Oscillator Frequency Threshold cycle Upper pp V 14 + High, a1 + V 14 + Low, a2 + Lower Oscillator current Frequency tolerance a3 + VTL VS Pin6 V T100 VS V Tt100 VS f a1 a2 a3 Iosc f 10 0.68 0.65 0.26 26 6.0 0.7 0.67 0.28 40 9.9 2000 0.72 0.69 0.3 54 13.5 mA Hz Hz I4 = 500 mA V2 = 0 V Pin 4 V4 6.9 7.4 8.0 V Test Conditions / Pins V14 = Low level
V14 = High level, I13 > | I14 |
Symbol I14 Pin 2 I2
Min. 1.0 -1.0 -20
Typ.
Max.
Unit mA
-40
-60
mA
VBatt = 12 V C4 open, C2 = 470 nF, duty cycle = 50%
*)
Reference point is battery ground.
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Rev. A3, 11-Apr-01
Application
VBatt
C5 330 nF 11 VS VS + Ich 10 mV 12 Idis - + Reset 2I Switch - on delay 13 C3 Reset VS Voltage doubler + - - Current limiting 90 mV VS VS C4 47 pF VS VS Rsh 16 9
Rev. A3, 11-Apr-01
- I + Oscillator 47 nF Overvoltage monitoring stage 2 VS Reset 820 kW Low voltage monitoring 2 1 7 NC 150 W R3 Ground 8 NC 10 NC 15 NC Load RL 14 Overvoltage monitoring stage 1
5
100 W
6
C1
47 m F
R1
C2
22 nF
47 kW
Figure 2. Application
3
30 kW
4
R2
VS
C6
VS
U6084B
95 9757
7 (9)
U6084B
Package Information
Package SO16
Dimensions in mm
10.0 9.85 5.2 4.8 3.7
1.4 0.4 1.27 8.89 16 9 0.25 0.10 0.2 3.8 6.15 5.85
technical drawings according to DIN specifications
13036
1
8
8 (9)
Rev. A3, 11-Apr-01
U6084B
Ozone Depleting Substances Policy Statement
It is the policy of Atmel Germany GmbH to 1. Meet all present and future national and international statutory requirements. 2. Regularly and continuously improve the performance of our products, processes, distribution and operating systems with respect to their impact on the health and safety of our employees and the public, as well as their impact on the environment. It is particular concern to control or eliminate releases of those substances into the atmosphere which are known as ozone depleting substances (ODSs). The Montreal Protocol (1987) and its London Amendments (1990) intend to severely restrict the use of ODSs and forbid their use within the next ten years. Various national and international initiatives are pressing for an earlier ban on these substances. Atmel Germany GmbH has been able to use its policy of continuous improvements to eliminate the use of ODSs listed in the following documents. 1. Annex A, B and list of transitional substances of the Montreal Protocol and the London Amendments respectively 2. Class I and II ozone depleting substances in the Clean Air Act Amendments of 1990 by the Environmental Protection Agency (EPA) in the USA 3. Council Decision 88/540/EEC and 91/690/EEC Annex A, B and C (transitional substances) respectively. Atmel Germany GmbH can certify that our semiconductors are not manufactured with ozone depleting substances and do not contain such substances.
We reserve the right to make changes to improve technical design and may do so without further notice. Parameters can vary in different applications. All operating parameters must be validated for each customer application by the customer. Should the buyer use Atmel Wireless & Microcontrollers products for any unintended or unauthorized application, the buyer shall indemnify Atmel Wireless & Microcontrollers against all claims, costs, damages, and expenses, arising out of, directly or indirectly, any claim of personal damage, injury or death associated with such unintended or unauthorized use. Data sheets can also be retrieved from the Internet: http://www.atmel-wm.com
Atmel Germany GmbH, P.O.B. 3535, D-74025 Heilbronn, Germany Telephone: 49 (0)7131 67 2594, Fax number: 49 (0)7131 67 2423
Rev. A3, 11-Apr-01
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