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) Applications ❑ Color LCD Backlighting ❑ Cell phones, smart phones ❑ PDAs, pocket PCs ❑ Organizers ❑ Digital Cameras ❑ MP3 Players 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. 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 Package Option Device Demo Kit MLP (3mm x 3mm) HV9903 HV9903K6* HV9903DB1 *Product supplied on 3000 piece carrier tape reels Absolute Maximum Ratings VDD 6V VSW , SW Voltage +35V VSHDN -0.5V to 6V IRset 10mA VRset VDD + 0.5V Storage Temperature -65ºC to +150ºC Operating Temperature -40ºC to +85ºC Recommended Operating Conditions Symbol VDD Parameter Min Supply voltage 2.6 ISW(pk) Peak switch current TAMB Operating temperature ILED LED current Specifications Symbol OVP Typ Max Unit 4.6 V 600 mA -40 85 ºC 5 40 mA Conditions (unless otherwise specified: TA = 25ºC, VDD = 2.6V) Parameter Min Typ. Max Unit Over voltage protection 28 33 35 V Conditions IDD VDD supply current 1.6 mA VRset =0.2V IDDQ Total leakage current when disabled (ISW(off) + IDD(off) + ILED(off)) 500 nA VSHDN =0V, RSET = 1.5KΩ RSW Switch on resistance 0.6 1.0 Ω VDD = 2.7V Switch current limit 900 mA VRset Rset pin voltage 100 mV RSET = 1.5KΩ VLED LED pin voltage mV RSET = 1.5KΩ, VDD < VOUT ILED LED pin current ISW(lim) TC ILED Tempco 180 5 RSET = 4.53KΩ 12.5 15 17.5 17 20 23 25 30 36 RSET = 750Ω 33 38 45 RSET = 562Ω 0.02 2 RSET = 1.5KΩ mA mA/ºC RSET = 1.13KΩ ILED = 15mA HV9903 HV9903 Symbol Parameter ISHDN Min Typ. SHDN input current Max Unit Conditions -100 nA VSHDN = 0V 100 fSW Inductor switching frequency DMAX 0.8 1.2 90 95 Maximum duty cycle VIL IC Shutdown voltage (SHDN pin), Off VIH IC Start-up voltage (SHDN pin), On 1.2 VOpen Open LED indicator at RSET lead 2.0 ISW(off) Switch Off leakage current Pin Configuration VDD SW GND LED SHDN RSET Pin VDD = 2.6 to 4.6V % V VDD0.4V VDD V VOUT > 33V, RSET = 562Ω, VDD = 2.7V 100 nA VSW = 5V Name Description 1 SW 2 GND Ground. The underside pads are internally connected to pin 2. 3 LED Cathodes of the LEDs are connected to this pin. 4 RSET For programming the LED current and dimming function. Internal switch connection. 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. Pin 1 Bottom View MHz 0.9 Top View GND 1.6 VSHDN = 2V 5 SHDN 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. 6 VDD Input voltage supply pin. It is common practice to use a bypass capacitor as close as possible to the device on this pin. 3 HV9903 HV9903 Functional Block Diagram L D VDD CDD COUT VDD SW HV9903 PWM OVP LED 1. 2MHz R S enable Q Soft Start ILED SHDN err amp VDD 100mV 22. 5V RSET VDD current mirror 1:3 7 5R RSET Fault R GND RSET Note: This drawing is a generalized representation of the HV9903. Actual internal circuitry may differ. Operation 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 66kΩ, 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 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. 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. 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 = 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 22.5V R SET Current through the RSET pin is monitored. If it falls below 1.5µA, both the PWM boost converter switch 4 HV9903 HV9903 inductor rating. Choosing an inductor with lower resistance results in more efficient operation. 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 Value for 2.7V Operation Soft Start 100 H Select the next lower standard value, taking inductor tolerance into account. Inductor Value SHDN IIN 50mA/div ILED 5mA 10 H 10mA 15mA ILED 20mA 25mA 30mA 35mA 40mA 1 H 10mA/div 5V 10V 15V 20V 25V VLED-STRING + (ILED · 5? ) + VD VLED-STRING + (ILED -5Ω) +VD Inductor Rating for 2.7V Operation 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. 40mA 1A 35mA 30mA 25mA Exceeds max recommended SW current 20mA 15mA Peak Inductor Current 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. 10mA 5mA 100mA ILED Apply correction factor and select an inductor with an equal or higher rating. Inductor Selection 10mA 5V 10V 15V 20V 25V VLED-STRING + (ILED · 5? ) + VD 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 VLED-STRING + (ILED -5Ω) +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 3.7µH and rating is 320mA. The next 5 HV9903 HV9903 lower standard value is 3.3µH (10% tolerance) and the corrected rating is then: ICORRECTED 320 mA 3.7µH 3.3µH 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. 359 mA 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 Inductance ideal SW Waveform Showing Inductor Saturation VIN Gnd Inductance too high VIN Gnd (continuous mode) Normal VIN Gnd Saturated Capacitor Selection Gnd Proper selection of CDD and COUT is essential to the efficient operation of the LED driver. Both CDD and COUT should be around 1µF 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. Note: ringing or noise may be present. 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 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. 6 HV9903 HV9903 Diode Selection DC Dimming Frequency Response 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 ILED Response (dB) 0 -10 -20 -30 -40 -50 100 1k 10k 100k Frequency (Hz) 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. 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 DC dimming is accomplished by applying a bias to the RSET resistor. L D VDD DC Dimming HV9903 COUT L D VDD HV9903 COUT 1 SW 2 GND 3 LED SHDN 5 ILED ( avg) Shutdown RSET 4 RBIAS VDIM RSET ILED 225 100mV RSET 2 GND 3 LED CDD VDD 6 1 SW VDIM 100mV RBIAS 7 D 22.5V R SET CDD VDD 6 SHDN 5 PWM RSET 4 RSET HV9903 HV9903 PWM Dimming via RSET DC dimming may be implemented in discrete steps using logic signals, as shown below. L D Multi-level Logic Dimming VDD HV9903 COUT CDD VDD 6 1 SW 2 GND SHDN 3 LED 5 VDD Shutdown RSET 4 HV9903 PWM RSET ILED ( avg) (1 D) L D COUT 22.5V R SET 1 SW CDD VDD 6 2 GND SHDN 3 LED RSET 5 Shutdown 4 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 L D VDD HV9903 COUT CDD VDD 6 1 SW 2 GND SHDN 3 LED 5 Shutdown RSET 4 PWM RSET R PWM R SET 2-cell Alkaline Circuit RPWM L D 1.8–3.0V VHI 1 100mV CIN HV9903 ILED ( avg) 225 (1 D) 100 mV 100 mV VLO R SET R PWM COUT 1 SW 2 GND 3 LED VDD 6 SHDN 5 RSET 4 2.6–4.6V Shutdown Fault RSET 8 VDD CDD HV9903 HV9903 Board Layout 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 1µF. In selecting the inductor, use the following graphs. 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. Inductor Value for 1.8V Operation Inductor Value 100 H The following schematic depicts the high frequency paths and their enclosed areas. Select the next lower standard value, taking inductor tolerance into account. L D VDD 10 H ILED ILED 20mA 25mA 30mA 35mA 40mA 5mA CDD 10mA 15mA 1 H 5V 10V 15V 20V 25V Keep these areas small VLED-STRING + (ILED · 5? ) + VD VLED-STRING + (ILED -5Ω) +VD HV9903 1 SW COUT SW closed SW open VDD 6 2 GND SHDN 5 3 RSET 4 LED The following PCB layout is recommended. 40mA 35mA 30mA 25mA 20mA Exceeds max recommended SW current 15mA Peak Inductor Current 10mA VDD 5mA L D ILED CDD 100mA HV9903 COUT Apply correction factor and select an inductor with an equal or higher rating. 10mA 5V 10V 15V 20V 25V VLED-STRING + (ILED · 5? ) + VD VLED-STRING + (ILED -5Ω) +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 GND Fault RSET Keep ground connection seperate and direct to pin 2 Inductor Rating for 1.8V Operation 1A Shutdown RSET SHDN HV9903 HV9903 Split Supply Operation It is also good practice to run the LED’s supply and return traces as close together as possible, reducing 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. 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. 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. L D VIN CIN HV9903 COUT 1 SW 2 GND 3 LED VDD 6 SHDN 5 RSET 4 2.6–4.6V Shutdown Fault RSET 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 VDD CDD HV9903 HV9903 Typical Performance COUT=Murata GRM32RR71H105KA01L, LEDs = Nichia NSPW500BS, D = Zetex ZHCS400 or ZHCS500 L D VIN CIN HV9903 COUT 1 SW VDD 6 2.6–4.6V 2 GND SHDN 5 Shutdown 3 LED RSET 4 VDD CDD Fault RSET VDD = VIN CIN L RSET COUT LEDs IIN VOUT 3.3V 10.0µF 4.7µH, Murata LQH32CN4R7M11 1.5KΩ 1.0µF, 50V 4 78.5mA 13.1V 6 111.2mA 19.4V ILED 15.5mA Other Examples COUT=Murata CRM32RR71H105KA01L, LEDs = Nichia NSPW500BS, D = Zetex ZHCS400 or ZHCS500 VDD = VIN CIN L RSET COUT LEDs IIN VOUT 3.3V 10.0µF 4.7µH, Murata LQH32CN4R7M11 1.0KΩ 1.0µF, 50V 4 111.3mA 13.6V 6 166.9mA 19.9V IIN VOUT ILED 13.0V 16.5mA 19.4V 16.5mA VDD VIN CIN L RSET COUT LEDs 1.8V 22.8mA 154.8 6.0V 3.0V ILED 10.0µF 9.0V 6.0V 4.7µH, Murata LQH32CN4R7M1 1 4 1.5KΩ 1.0µF, 50V 40.2mA 26.1mA 6 9.0V 63.4mA 41.3mA VDD = VIN CIN L RSET COUT LEDs IIN VOUT ILED 3.3V 10.0µF 10µH, Murata LQH2MC100K02 1.5KΩ 1.0µF, 50V 4 77.9mA 12.92V 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 . 0.118 3.0 TOP VIEW 0.005 0.125 10° + 2° 0.039 ± 0.002 0.7 ± 0.05 SIDE VIEW SEATING PLANE 0.008 ± 0.002 0.2 ± 0.05 Exposed Pad 0.037 0.95 0.015 ± 0.002 0.38 ± 0.05 HEAT SLUG Measurement = Inches millimeters BOTTOM VIEW 0.048 1.22