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| HV9903 Initial Release White LED Driver Features Power efficiency of up to 85% Drives up to 6 White LEDs 2.6V to 4.6V Supply power stage can operate at 1.8V (see page 8) Built-in Soft Start DC and PWM Dimming Control Built-in Open LED protection Open LED indicator (via RSET) 1.2MHz Fixed Switching Frequency 500nA max leakage current when disabled No leakage current path through LEDs when disabled Resistor-programmable LED Current Small 6-lead MLP (3mm x 3mm) package (similar to 6-pin SOT-23) Description The Supertex HV9903 is a fixed frequency DC-DC boost converter designed for driving Light Emitting Diodes (LEDs) with constant current where the light intensity is proportional to the current through them. The input supply voltage range into the device (VDD) is 2.6 to 4.6V. Operation of the driver at lower voltages is possible as long as a 2.6-4.6V lowcurrent supply is available for the HV9903. The device uses a single inductor and a minimum number of passive components. The device can be enabled/disabled via the SHDN pin. The HV9903 has an internal oscillator. The oscillator frequency is at fixed frequency of 1.2MHz that allows use of small value inductors. The LED current can be adjusted from 5 to 40mA by an external resistor connected between the RSET and the GND pins. The amount of current though the LED can also be adjusted via DC voltage or a pulse width modulated (PWM) signal to the RSET pin. Soft-start is implemented on-chip, minimizing inrush current to only 30% over steady state current. An open LED circuit detects an open LED condition, disables the driver, and sets the RSET pin high. The driver is re-enabled by asserting SHDN low, then high. If the open LED condition persists, the driver will again latch off. Applications Color LCD Backlighting Cell phones, smart phones PDAs, pocket PCs Organizers Digital Cameras MP3 Players Typical Application Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the Supertex website: http://www.supertex.com. For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website. HV9903 HV9903 Ordering Information Device HV9903 Package Option MLP (3mm x 3mm) Demo Kit HV9903DB1 HV9903K6* *Product supplied on 3000 piece carrier tape reels Absolute Maximum Ratings VDD VSW , SW Voltage VSHDN IRset VRset Storage Temperature Operating Temperature 6V +35V -0.5V to 6V 10mA VDD + 0.5V -65C to +150C -40C to +85C Recommended Operating Conditions Symbol VDD ISW(pk) TAMB ILED Parameter Supply voltage Peak switch current Operating temperature LED current -40 5 Min 2.6 Typ Max 4.6 600 85 40 Unit V mA C mA Conditions Specifications Symbol OVP IDD IDDQ Parameter (unless otherwise specified: TA = 25C, VDD = 2.6V) Min 28 Typ. 33 Max 35 1.6 500 Unit V mA nA VRset =0.2V VSHDN =0V, RSET = 1.5K Conditions Over voltage protection VDD supply current Total leakage current when disabled (ISW(off) + IDD(off) + ILED(off)) Switch on resistance Switch current limit Rset pin voltage LED pin voltage LED pin current RSW ISW(lim) VRset VLED ILED 0.6 900 100 1.0 mA mV VDD = 2.7V RSET = 1.5K RSET = 1.5K, VDD < VOUT RSET = 4.53K 180 5 12.5 17 25 33 15 20 30 38 0.02 2 mV 17.5 23 36 45 mA/C mA RSET = 1.5K RSET = 1.13K RSET = 750 RSET = 562 ILED = 15mA TC ILED Tempco HV9903 HV9903 Symbol ISHDN Parameter SHDN input current Min Typ. Max -100 100 fSW DMAX VIL VIH VOpen ISW(off) Inductor switching frequency Maximum duty cycle IC Shutdown voltage (SHDN pin), Off IC Start-up voltage (SHDN pin), On Open LED indicator at RSET lead Switch Off leakage current 1.2 2.0 VDD0.4V VDD 100 V nA VOUT > 33V, RSET = 562, VDD = 2.7V VSW = 5V 0.8 90 1.2 95 0.9 V 1.6 MHz % Unit nA Conditions VSHDN = 0V VSHDN = 2V VDD = 2.6 to 4.6V Pin Configuration Pin 1 2 3 4 Name Description SW GND LED RSET Internal switch connection. Ground. The underside pads are internally connected to pin 2. Cathodes of the LEDs are connected to this pin. For programming the LED current and dimming function. Also functions as a Fault output to indicate an open LED condition. RSET is pulled to VDD when an open LED condition is detected. The driver is then latched off. To reset, the SHDN input must be asserted low. An externally applied voltage greater than 100mV causes the LED switch and PWM boost converter to shut off. The IC does not go into low power standby and the soft-start circuit is not reactivated when VRset again falls below 100mV. SW GND LED VDD SHDN RSET Top View GND Pin 1 5 SHDN VDD Shut down input. A logic low disables the IC and places it in low power standby. A logic high enables the IC via a soft-start sequence. Input voltage supply pin. It is common practice to use a bypass capacitor as close as possible to the device on this pin. Bottom View 6 3 HV9903 HV9903 Functional Block Diagram L VDD CDD VDD SW D COUT HV9903 OVP R S Q PWM 1. 2MHz enable LED Soft Start err amp SHDN ILED 22. 5V RSET VDD 100mV current mirror VDD 1:3 7 5R R GND Fault RSET RSET Note: This drawing is a generalized representation of the HV9903. Actual internal circuitry may differ. Operation The HV9903 operates as a boost converter that regulates output current rather than output voltage. To maintain constant output current, LED current is monitored via the LED pin and the boost converter's PWM duty cycle is adjusted accordingly to maintain the desired current level. LED current is controlled 100% via the PWM boost converter - the MOSFET connected to the LED pin is fully turned on during normal operation and is not regulated to maintain constant LED current. This minimizes voltage drop at the LED pin, maximizing overall efficiency. LED current is set by the value of the resistor connected to the RSET pin. The voltage at the RSET pin is maintained at 100mV and the resulting current through the RSET resistor is used as a reference for LED current control. LED current is regulated at 225 times RSET current. I LED = 22.5V R SET and LED switch are turned off. Soft-start is not reset and the IC does not go into low power standby. Such a condition can occur two ways: 1) if RSET is greater than about 66k, or 2) an external voltage greater than 100mV is applied to the RSET pin. Internal blocking prevents reverse current flow into the RSET pin if the externally applied voltage exceeds 100mV. However, applied voltage must not exceed VDD. The control loop is designed for discontinuous mode operation. That is, inductor current is allowed to return to zero between PWM conversion cycles. To assure discontinuous mode operation, the inductor value must be below a certain value for given conditions of supply voltage and LED string voltage drop. The Inductor Selection section provides further information. The PWM boost converter is a current mode controller operating at an internally fixed 1.2MHz. A soft-start circuit minimizes inrush current when power is initially applied or the device is enabled via the SHDN input. Inrush current is typically limited to 130% of steady-state current. Although the soft-start period is short (~1ms), it means that if using SHDN for PWM dimming, the PWM dimming signal should be 4 Current through the RSET pin is monitored. If it falls below 1.5A, both the PWM boost converter switch HV9903 HV9903 fairly low frequency so that the 1ms soft-start interval does not introduce much error. The RSET input is better for PWM dimming, as it does not include softstart. (See below for PWM dimming techniques.) inductor rating. Choosing an inductor with lower resistance results in more efficient operation. Inductor Value for 2.7V Operation Soft Start 100 H SHDN Inductor Value Select the next lower standard value, taking inductor tolerance into account. ILED 10 H 5mA IIN 50mA/div 10mA 15mA 20mA 25mA 30mA 35mA 40mA ILED 10mA/div 1H 5V 10V 15V 20V 25V VLED-STRING + (ILED * 5? ) + VD VLED-STRING + (ILED -5) +VD Open LED Protection Open LED protection is integrated into the HV9903. Without open LED protection, output voltage would climb to destructive levels as the driver attempts to correct for the open LED condition. Should the voltage at the SW pin exceed 33V, the driver latches off and the RSET pin is pulled to VDD, indicating a fault condition. To reset the latch, assert SHDN low for at least 200ns. When SHDN is again brought high, the driver will be re-enabled, including soft-start. If the open LED condition persists, the HV9903 will again latch off. Peak Inductor Current Inductor Rating for 2.7V Operation 1A Exceeds max recommended SW current 40mA 35mA 30mA 25mA 20mA 15mA 10mA 5mA 100mA ILED Apply correction factor and select an inductor with an equal or higher rating. Inductor Selection The HV9903 is designed for discontinuous mode operation. Control loop stability may be compromised if the converter is allowed to operate in continuous mode. To assure discontinuous mode operation, the inductor must not exceed a certain value depending on supply voltage, output current, and output voltage. The following graphs show the maximum permissible inductor value and inductor current rating for a lithiumion battery application (2.7V minimum battery voltage). When calculating LED string voltage drop, use maximum LED voltage. If using paralleled LED strings with current balancing resistors, include the resistor voltage drop in VLED-STRING. VD is the diode's forward voltage drop. Always select the next lower standard value inductor and be conservative on 10mA 5V 10V 15V 20V 25V VLED-STRING + (ILED * 5? ) + VD VLED-STRING + (ILED -5) +VD When selecting the next lower standard value inductor, the current rating must be adjusted according to the following equation. ICORRECTED IGRAPH LGRAPH LSELECTED As an example, 4 LEDs with 4V max drop are to be driven at 20mA. LED string drop is 16V plus 0.6V for the diode plus 0.1V for LED pin voltage, for a total of 16.7 volts. From the graphs, inductor value at 16.7V and 20mA is 3.7H and rating is 320mA. The next 5 HV9903 HV9903 lower standard value is 3.3H (10% tolerance) and the corrected rating is then: ICORRECTED 320 mA 3.7H 3.3H 359 mA indicated when the SW voltage is at the supply voltage level (with some ringing). The following graphs show the SW waveform with various inductor values and can assist in selecting an inductor. The top graph shows an inductor value that is acceptable, however, greater efficiency can be achieved by increasing inductance. The bottom graph shows continuous mode operation, which must be avoided. Inductor data sheets may rate the inductor in terms of DC current, RMS current, or saturation current. The DC or saturation ratings should be used. Confirm that the inductor is not saturating by observing the SW pin. When an inductor saturates, current begins to climb rapidly. This condition is evidenced by a breakpoint in the SW voltage waveform as indicated in the diagram below. Normally, the voltage at the SW pin should be a fairly linear ramp, as the linear rise in inductor current through the SW resistance produces a linear voltage ramp. When the inductor saturates, the rapid rise in current produces a likewise rapid rise in SW voltage. Test using an HV9903 with a low switching frequency. SW Waveform with Various Inductor Values Inductance too low VIN Gnd idle time SW Waveform Showing Inductor Saturation Inductance ideal VIN Gnd VIN Gnd Inductance too high (continuous mode) Normal Saturated VIN Gnd Gnd Note: ringing or noise may be present. Capacitor Selection Proper selection of CDD and COUT is essential to the efficient operation of the LED driver. Both CDD and COUT should be around 1F with good high frequency characteristics (low ESR and ESL). Ceramic capacitors are a practical choice for their high volumetric efficiency and good high frequency characteristics, but pay attention to the capacitor's voltage coefficient. Some small, high value ceramic capacitors can lose 75% of their capacitance at their rated voltage! X5R, Y5V, and Z5U formulations are more susceptible to this effect, as well as possessing higher temperature coefficients. X7R formulations are a better choice. The voltage rating of CDD should be greater than the maximum supply voltage. To be compatible with the HV9903's open LED protection, COUT's voltage rating should be 35V or more. Also, confirm that the driver is operating in discontinuous mode by observing the voltage at the SW pin while at minimum supply and maximum LED current. For worst-case test purposes, select components within their tolerance range as follows: Inductor: high value LED: high voltage drop HV9903: high switching frequency Some ringing in the SW waveform will be evident, but is not a concern as the energy is very low. About 1015% idle time should be allowed to assure discontinuous mode operation. Idle time is the interval when there is no inductor current flowing, as 6 HV9903 HV9903 Diode Selection Since the HV9903 operates at a 1.2MHz switching frequency, the output rectifier must be fast - 20ns or less. The faster the diode, the more efficiently the driver operates. Also, choose a diode with low capacitance to improve performance. A Schottkey need not be used, although its lower forward voltage drop improves efficiency. Peak current rating is the same as for the inductor. Average current is simply the LED current. To be compatible with the HV9903's open LED protection, the diode's reverse voltage rating should be 35V or more. Otherwise, the diode's voltage rating should be greater than the LED string's voltage drop plus 1 volt. +10 0 DC Dimming Frequency Response ILED Response (dB) -10 -20 -30 -40 -50 100 1k 10k 100k Dimming Dimming may be accomplished in one of two ways: DC dimming or PWM dimming. DC dimming linearly regulates the current through the LEDs in a continuous fashion, while PWM dimming rapidly turns the LEDs on and off while maintaining a constant `on' current. In PWM dimming, the ratio of on to off time determines perceived brightness. The on/off frequency must be high enough to prevent visible flickering - typically above 70Hz. The claimed advantage of PWM dimming is less color shift as the LED is dimmed, although the effect is virtually imperceptible. DC dimming is accomplished by applying a bias to the RSET resistor. Frequency (Hz) PWM dimming may be implemented via the SHDN input or via RSET. Since SHDN reactivates soft-start, a delay is introduced (~1ms) to LED turn-on. For this reason, it is better to use the RSET pin for PWM dimming, as it does not include the soft-start delay. PWM dimming frequency should be in the range of 70-100Hz to minimize the effect of turn-on delays while avoiding flicker. PWM Dimming via SHDN D L VDD DC Dimming D L VDD HV9903 COUT 1 SW 2 GND 3 HV9903 COUT 1 SW 2 GND 3 LED VDD 6 SHDN 5 CDD PWM RSET 4 VDD 6 SHDN 5 CDD ILED ( avg) Shutdown RBIAS RSET VDIM D 22.5V R SET RSET LED RSET 4 ILED 225 100mV RSET VDIM 100mV RBIAS 7 HV9903 HV9903 PWM Dimming via RSET D L VDD HV9903 COUT 1 SW 2 GND 3 LED DC dimming may be implemented in discrete steps using logic signals, as shown below. Multi-level Logic Dimming D L VDD VDD 6 SHDN 5 CDD Shutdown PWM RSET RSET 4 HV9903 COUT 1 SW 2 GND 3 LED VDD 6 SHDN RSET 5 4 CDD Shutdown ILED ( avg) (1 D) 22.5V R SET RSET The logic signal must have a low output impedance relative to RSET and be capable of going to within a few millivolts of ground. The following modification provides higher immunity to the logic low voltage level (VLO). It also minimizes the effect of voltage differences between the HV9903's ground and the PWM signal source's ground. Dual-cell Alkaline Operation The HV9903 LED driver may be used in 2-cell alkaline battery applications (1.8V min) by powering the power stage directly from the batteries, while powering the HV9903 from an available 3.3V supply. Supplying the power stage directly from the batteries reduces the load on the 3.3V supply, which in turn increases overall efficiency and keeps components small. The same dimming techniques used in the single-supply application may be used in this dual-supply application. PWM Dimming via RSET D L VDD HV9903 COUT 1 SW 2 GND 3 LED VDD 6 SHDN 5 CDD Shutdown PWM RSET RPWM 2-cell Alkaline Circuit D L 1.8-3.0V RSET 4 R PWM ILED ( avg) R SET VHI 1 100mV HV9903 CIN COUT 1 SW 2 GND 3 LED 225 (1 D) 100 mV 100 mV VLO R SET R PWM VDD 6 SHDN 5 2.6-4.6V VDD CDD Shutdown Fault RSET RSET 4 8 HV9903 HV9903 Component selection is similar to the Li-ion battery application with the exception of the inductor and CDD capacitor. Since high current is no longer being drawn from VDD, CDD may be lowered to around 10nF. CIN should be 1F. In selecting the inductor, use the following graphs. Board Layout Since high frequencies are involved, PCB layout is critical. To minimize parasitic inductance and radiated EMI, the loop area of the high frequency paths must be kept to a minimum. Second, try to keep the two loop areas as concentric as possible. Lastly, make traces as short and wide as possible. To avoid LED current errors, keep the RSET ground connection separate from high current ground paths and connect directly to pin 2. The following schematic depicts the high frequency paths and their enclosed areas. Inductor Value for 1.8V Operation 100 H Inductor Value Select the next lower standard value, taking inductor tolerance into account. 10 H ILED 20mA 25mA 30mA 35mA 40mA ILED 5mA D L CDD VDD HV9903 VDD 6 COUT 1 SW 2 3 10mA 15mA GND SHDN 5 LED RSET 4 Shutdown Fault RSET 1H 5V 10V 15V 20V 25V VLED-STRING + (ILED * 5? ) + VD Keep these areas small SW closed SW open VLED-STRING + (ILED -5) +VD Keep ground connection seperate and direct to pin 2 Inductor Rating for 1.8V Operation The following PCB layout is recommended. 1A 40mA 35mA 30mA 25mA 20mA 15mA 10mA Exceeds max recommended SW current Peak Inductor Current 5mA VDD D L CDD HV9903 SHDN ILED 100mA Apply correction factor and select an inductor with an equal or higher rating. COUT GND RSET 10mA 5V 10V 15V 20V 25V VLED-STRING + (ILED * 5? ) + VD VLED-STRING + (ILED -5) +VD Don't forget to apply the correction factor and confirm that the inductor is not saturating and the driver is operating in discontinuous mode, as outlined earlier. 9 HV9903 HV9903 It is also good practice to run the LED's supply and return traces as close together as possible, reducing the loop area of the LED path. Running the return trace on a separate layer directly underneath the supply trace would be the ideal layout. Split Supply Operation The HV9903 LED driver may be used in Split Supply application by powering the power stage directly from the batteries, while powering the HV9903 (VDD) from an available regulated supply within 2.6V to 4.6V. The power stage voltage (VIN) can be higher than 4.6V so long as the inductor is being operated in discontinues mode. Supplying the power stage directly from the batteries reduces the load on the regulated supply, which in turn increases overall efficiency and keeps components small. The same dimming techniques used in the single-supply application may be used in this dual-supply application. D L CIN HV9903 COUT 1 SW 2 GND 3 LED VIN 2.6-4.6V Shutdown Fault RSET VDD 6 SHDN 5 VDD CDD RSET 4 The 3 pads along the centerline on the underside of the HV9903 are internally connected to pin 2 and need not be connected externally to ground. The HV9903's MLP package fits in most pad layouts designed for a 6-pin SOT-23. 10 HV9903 HV9903 Typical Performance COUT=Murata GRM32RR71H105KA01L, LEDs = Nichia NSPW500BS, D = Zetex ZHCS400 or ZHCS500 D L CIN HV9903 COUT 1 2 3 VIN 2.6-4.6V Shutdown Fault RSET SW VDD 6 VDD CDD GND SHDN 5 LED RSET 4 VDD = VIN 3.3V CIN 10.0F L 4.7H, Murata LQH32CN4R7M11 RSET 1.5K COUT 1.0F, 50V LEDs 4 6 IIN 78.5mA 111.2mA VOUT 13.1V 19.4V ILED 15.5mA Other Examples COUT=Murata CRM32RR71H105KA01L, LEDs = Nichia NSPW500BS, D = Zetex ZHCS400 or ZHCS500 VDD = VIN 3.3V CIN 10.0F L 4.7H, Murata LQH32CN4R7M11 RSET 1.0K COUT 1.0F, 50V LEDs 4 6 IIN 111.3mA 166.9mA VOUT 13.6V 19.9V ILED 22.8mA VDD VIN 1.8V 6.0V CIN L RSET COUT LEDs IIN 154.8 VOUT ILED 3.0V 9.0V 6.0V 9.0V 10.0F 4.7H, Murata LQH32CN4R7M1 1 4 1.5K 1.0F, 50V 6 40.2mA 26.1mA 63.4mA 41.3mA 13.0V 16.5mA 19.4V 16.5mA VDD = VIN 3.3V CIN 10.0F L 10H, Murata LQH2MC100K02 RSET 1.5K COUT 1.0F, 50V LEDs 4 IIN 77.9mA VOUT 12.92V ILED 16.8mA 10/7/03 11 1235 Bordeaux Drive * Sunnyvale * CA * 94089 Telephone: (408) 222-8888 * Fax: (408) 222-4895 Package Outlines 6-Lead MLP Package Outline (k6) (3mm x 3mm) 0.118 3.0 0.005 0.125 . TOP VIEW 0.005 0.125 10 + 2 0.118 3.0 0.039 0.002 0.7 0.05 SIDE VIEW 0.008 0.002 0.2 0.05 Exposed Pad SEATING PLANE 0.037 0.95 0.015 0.002 0.38 0.05 HEAT SLUG Measurement = Inches millimeters BOTTOM VIEW 0.048 1.22 |
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