Version : PRE.001 Issue Date : 2006/5/1 File Name : SP--PRE.001.doc Total Pages : 25 16-bit Constant Current LED Driver with Error Detection
16-bit Constant Current LED Driver with Error Detection General Description is a constant-current sink driver specifically designed for LED display applications. The device incorporates shift registers, data latches, and constant current circuitry on the silicon CMOS chip. The maximum output current value of all 16 channels is adjustable by a single external resistor. Its built-in open/short detection circuits help users detect LED failures. System retrieve the error messages to indicate which channel has failure by serial output data. The thermal shutdown function provides the over temperature protection. Features Constant-current outputs: 5mA to 90mA adjustable by one external resistor Maximum output voltage: 17V Maximum clock frequency: 25MHz Built-in real-time LED open/short detection Fast detecting response: 0.1us (min.) Over temperature protection: thermal shutdown (junction temperature > 180 C) Package and pin assignment compatible to conventional LED drivers (ST2221C, DM134/5/6) Power supply voltage: 3.3V to 5.5V Applications Indoor/Outdoor LED Video Display LED Variable Message Signs (VMS) System Package Types PDIP24, SOP24, SSOP24 or QFN32 (with thermal pad) 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 1
Block Diagram 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 2
Pin Connection REXT DAO EN GND OUT15 OUT14 OUT13 OUT12 OUT11 OUT10 OUT9 OUT8 OUT7 OUT6 OUT5 OUT4 25 26 27 28 29 30 31 24 23 22 21 20 19 18 17 16 15 14 QFN32 (bottom view) 13 12 11 10 32 1 2 3 4 5 6 7 8 9 GND GND VDD VDD GND GND GND GND DAI DCK LAT GND OUT0 OUT1 OUT2 OUT3 Pin Description PIN No. PIN NAME FUNCTION PDIP24/SOP24/SSOP24: 1 QFN32: 1, 2, 5, 6, 7, 8, 12, 29, Thermal pad GND Ground terminal. PDIP24/SOP24/SSOP24: 2 QFN32: 9 DAI Serial data input terminal. PDIP24/SOP24/SSOP24: 3 QFN32: 10 DCK Synchronous clock input terminal for serial data transfer. Data is sampled at the rising edge of DCK. PDIP24/SOP24/SSOP24: 4 QFN32: 11 LAT Input terminal of data strobe. Data on shift register goes through at the rising edge of LAT (edge trigger). Otherwise, data is latched. PDIP24/SOP24/SSOP24: 5~20 QFN32: 13~28 PDIP24/SOP24/SSOP24: 21 QFN32: 30 PDIP24/SOP24/SSOP24: 22 QFN32: 31 OUT0~15 EN DAO Sink constant-current outputs (open-drain). Output enable terminal: H for all outputs are turned off, L for all outputs are active. Serial data output terminal. PDIP24/SOP24/SSOP24: 23 QFN32: 32 REXT External resistors connected between REXT and GND for output current value setting. PDIP24/SOP24/SSOP24: 24 QFN32: 3, 4 VCC Supply voltage terminal. 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 3
Equivalent Circuit of Inputs and Outputs 1. DCK, DAI, LAT, EN terminals 2. DAO terminals 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 4
Maximum Ratings (Ta=25 C, Tj(max) = 150 C) CHARACTERISTIC SYMBOL RATING UNIT Supply Voltage VCC -0.3 ~ 7.0 V Input Voltage VIN -0.3 ~ VCC+0.3 V Output Current IOUT 100 ma Output Voltage VOUT -0.3 ~ 17 V Input Clock Frequency FDCK 25 MHz GND Terminal Current IGND 1600 ma Power Dissipation (4 layer PCB) Thermal Resistance PD Rth(j-a) 2.5 ( PDIP24 : Ta=25 C) 1.58 ( SOP24 : Ta=25 C) 1.39 ( SSOP24 : Ta=25 C) 2.78 ( TSSOP24 : Ta=25 C) 3.08 ( QFN32 : Ta=25 C) 50.0 (PDIP24 ) 79.2 (SOP24 ) 90.2 (SSOP24 ) 45 ( TSSOP24) 40.6 ( QFN32 ) Operating Temperature Top -40 ~ 85 C Storage Temperature Tstg -55 ~ 150 C Recommended Operating Condition CHARACTERISTIC SYMBOL CONDITION MIN. TYP. MAX. UNIT Supply Voltage VCC 3.3 5.0 5.5 V Output Voltage VOUT Driver On *1 1.0 0.5VCC Output Voltage VOUT Driver Off *2 17 Output Current Input Voltage IO OUTn 5 90 IOH VOH = VCC 0.2 V +1.2 IOL VOL = 0.2 V -1.4 VIH 0.8VCC VCC VCC = 3.3 V ~ 5.5V VIL 0.0 0.2VCC Input Clock Frequency FDCK Single Chip Operation 25 MHz LAT Pulse Width tw LAT TBD DCK Pulse Width tw DCK TBD EN Pulse Width tw EN TBD Set-up Time for DAI tsetup(d) TBD Hold Time for DAI thold(d) VCC = 5.0V TBD Set-up Time for LAT tsetup(l) TBD Hold Time for LAT thold(l) TBD Set-up Time for Open/Short tsetup(os) TBD Open/Short Detection Response tdet TBD W C/W V ma V ns *1 Notice that the power dissipation is limited to its package and ambient temperature. *2 The driver output voltage including any overshoot stress has to be compliant with the maximum voltage (17V). 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 5
Electrical Characteristics (VCC = 5.0 V, Ta = 25 C unless otherwise noted) CHARACTERISTIC SYMBOL CONDITION MIN. TYP. MAX. UNIT Input Voltage H Level VIH CMOS logic level 0.8VCC VCC Input Voltage L Level VIL CMOS logic level GND 0.2VCC V Output Leakage Current IOL VOH = 17 V ±1.0 ua Output Voltage (S-OUT) VOL IOL = 1.4 ma 0.2 VOH IOH= 1.2 ma VCC-0.2 V Output Current Skew (Channel-to-Channel) *1 IOL1 ±3 % VOUT = 1.0 V Rrext = 2.2 KΩ Output Current Skew (Chip-to-Chip) *2 IOL2 TBD TBD TBD ma Output Voltage Regulation % / VOUT Rrext = 2.2 KΩ VOUT = 1 V ~ 3 V ±0.1 ±0.5 % / V Supply Voltage Regulation % / VCC Rrext = 2.2 KΩ ±1 ±4 LED Open Detection Threshold V(od) 0.3 all outputs turn on LED Short Detection Threshold V(sd) 0.5VCC Thermal Alarm Threshold T(alm) junction temperature Thermal Shutdown Threshold T(sht) V C I DD(off) power on all pins are open unless VCC and GND 2.8 I DD(off) input signal is static Rrext = 2.9 KΩ all outputs turn off 4.6 Supply Current *3 I DD(on) input signal is static Rrext = 2.9 KΩ all outputs turn on 5.8 ma I DD(on) input signal is static Rrext = 560 Ω all outputs turn off I DD(on) input signal is static Rrext = 560 Ω all outputs turn on *1 Channel-to-channel skew is defined as the ratio between (any Iout average Iout) and average Iout, where average Iout = (Imax + Imin) / 2. *2 Chip-to-Chip skew is defined as the range into which any output current of any IC falls. *3 IO excluded. 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 6
Switching Characteristics (VCC = 5.0V, Ta = 25 C unless otherwise noted) CHARACTERISTIC SYMBOL CONDITION MIN. TYP. MAX. UNIT Propagation Delay EN-to-OUT15 ( L to H ) LAT-to-OUT15 tplh VIH = VCC DCK-to-DAO VIL = GND EN-to-OUT15 Propagation Delay Rrext = 2.2 KΩ LAT-to-OUT15 tphl ( H to L ) DCK-to-DAO VL = 5.0 V Output Current Rise Time tor RL = 180 Ω Output Current Fall Time tof CL = 13 pf Output Delay Time (OUT(n)-to-OUT(n+1)) tod ns Switching Characteristics (VCC = 3.3V, Ta = 25 C unless otherwise noted) CHARACTERISTIC SYMBOL CONDITION MIN. TYP. MAX. UNIT Propagation Delay EN-to-OUT15 ( L to H ) LAT-to-OUT15 tplh VIH = VCC DCK-to-DAO VIL = GND EN-to-OUT15 Propagation Delay Rrext = 2.2 KΩ LAT-to-OUT15 tphl ( H to L ) DCK-to-DAO VL = 5.0 V Output Current Rise Time tor RL = 180 Ω Output Current Fall Time tof CL = 13 pf Output Delay Time (OUT(n)-to-OUT(n+1)) tod ns 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 7
Timing Diagram 1. DCK-DAI, DAO 2. DCK-LAT 3. LAT-OUT15 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 8
4. EN-OUT15 5. OUTn+1-OUTn 6. OS-LAT, DCK (EN= L ) 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 9
Constant-Current Output Constant-current value of each output channel is set by an external resistor connected between the REXT pin and GND. Varying the resistor value can adjust the current scale ranging from 5mA to 90mA. The reference voltage of REXT terminal (Vrext) is approximately 0.6V. The output current value is calculated roughly by the following equation: Iout(mA) 5 10 20 30 40 50 60 70 80 90 M 99.7 98.1 96.0 94.2 92.5 90.8 89.1 87.1 85.1 84.4 Output Current as a Function of Rrext value Iout (ma) 100 90 80 Vrext (V) Iout (ma) ~ 70 Rrext (KΩ) M 60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Rrext (KΩ) Output Current as a Function of Output Voltage Iout (ma) 100 90 80 70 60 50 40 30 20 10 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 Vout (V) In order to obtain a good performance of constant-current output, a suitable output voltage is necessary. Users can get related information about the minimum output voltage above. 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 10
Serial Data Interface The serial-in data (DAI) will be clocked into 16 bit shift register synchronized on the rising edge of the clock (DCK). The data 1 represents the corresponding current output ON, while the data 0 stands for OFF. The data will be transferred into the 16 bit latch synchronized on the rising edge (edge trigger) of the strobe signal (LAT); otherwise, the data will be held. The latch pulse should be sent after the falling edge of the last clock within a frame data. The trigger timing of the serial-out data (DAO) will be shifted out on synchronization to the rising edge of the clock. All outputs are turned off while enable terminal (EN) is kept at high level. And they are active when EN shifts to low. 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 11
Thermal Shutdown During operation, when the junction temperature of the IC will reach approximately above 180, it will cause the driver to shutdown all the outputs. Basically, the IC will cool down and return to the safe operating temperature which is approximately below 110. will restart all the outputs at the same time. Operation in the thermal situation for a long time may cause chip damage permanently. LED Open/Short Detection The result of open/short detection of could be retrieved from serial-out (DAO) data. It will be identified as a LED open failure when the output is turned on but the output voltage is below 0.3V. And then it will be identified as a LED short failure when the output is turned on but the output voltage is above 1/2 VCC. To set up with the following conditions: (1) the image data written in shift register corresponding to particular output channel is 1 ; (2) the output enable terminal is activated (EN= L ); (3) the rising edge of the latch signal (LAT), will execute LED open/short detection then renews the results within the corresponding shift register. By using the error message retrieved from serial-out data, system can recognize the status of every LED driven by each channel. For either LED open or short detection, the original image data is written to 1 but 0 is retrieved then a LED failure has occurred. If the image data is written to 0 or the output enable terminal is inactive (EN= H ), it will not execute any detection process for the corresponding channel. Therefore, system still retrieves the original image data. 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 12
Real-time monitor With the above operating principle, system could continuously retrieve LED status from serial-out then compare with the last frame data one by one. Once there is any discrepancy ( 1 0 ), we can locate which channel is abnormal precisely. Since the process is ongoing and without shifting between image mode and detection mode, it does not interrupt the image data flow and the output display. The real-time monitor method is suitable for LED Variable Message Signs (VMS) system. Clocks calculation For large LED display applications, real-time monitor could be a heavy loading for system because it needs to compare the retrieved information with a lot of frame data. Therefore, to write the image data of all channels to 1, all failure status will be identified when there will be any 0 retrieved. By calculating the numbers of clock pulses, the locations of abnormal channel could be pointed out easily. The clocks calculation method helps to minimize the loading and memory resources of system. Selection of Open/Short Detection The default detection type provided by is LED open detection after power-on. Users could switch LED open to short detection (or short to open detection) by following timing sequence. There are two alternative options could be selected. The option 1 shows triggering latch pulse when the last clock of the frame data kept at high level. The option 2 shows sending one useless clock pulse which will not shift-in data while the latch signal is kept at high level. useless clock pulse does not shift-in data Open Short or Short Open 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 13
Timing Diagram of LED Open/Short Detection 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 14
Threshold of Short Detection The default threshold voltage for LED short detection of is 1/2 VCC. One could change the default voltage by switching or setting a new voltage of VLED during short detection is going on. Please see the example below for reference: Note that the VSHORT should be satisfied with the following inequality: The new threshold voltage of short detection will be equivalent to: 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 15
Outputs Delay Large in-rush currents will occur when the system activates all the outputs at once. To reduce this effect, is designed to have a constant unit of delay (around 1.5ns) between outputs. The delay for every output goes like this: there is no delay for OUT15 and OUT7, 1 unit of delay for OUT14 and OUT6, 2 units of delay for OUT13 and OUT5 and so on. Global Brightness Control has no built-in global brightness control feature. In order to obtain a lower resolution of global brightness control effect, two methods could be utilized. One is providing PWM signal synchronized on latch pulse to modulate the output enable terminal (EN pin). The other is to adjust the Rrext value or voltage drop across the external resistor. Please see the reference circuit below: 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 16
Power Dissipation The power dissipation of a semiconductor chip is limited to its package and ambient temperature, in which the device requires the maximum output current calculated for given operating conditions. The maximum allowable power consumption can be calculated by the following equation: Pd(max)(Watt) = Tj(junction temperature)(max)( C) Ta(ambient temperature)( C) Rth(junction-to-air thermal resistance)( C/Watt) The relationship between power dissipation and operating temperature can be refer to the figure below: 4.0 Power Dissipation Pd(W) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 QFN32 TSSOP24 PDIP24 SOP24 SSOP24 Tj(max)=150 C Rth(QFN32)=40.6 C/Watt Rth(PDIP24)=50.0 C/Watt Rth(SOP24)=79.2 C/Watt Rth(SSOP24)=90.2 C/Watt Rth(TSSOP24)=45 C/Watt 0.0 0 20 40 60 80 100 120 140 160 Ambient Temperature Ta( C) The power consumption of IC can be determined by the following equation and should be less than the maximum allowable power dissipation: 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 17
Package Outline Dimension PDIP24 Unit: inch 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 18
Package Outline Dimension SSOP24 Unit: inch 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 19
Package Outline Dimension SOP24_A Unit: inch 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 20
Package Outline Dimension SOP24_B SYMBOL DIMENSION(mm) DIMENSION(mm) SYMBOL MIN. MAX. MIN. MAX. A 12.9 13.1 C3 0.05 0.2 A1 0.30 0.50 C4 0.80TYP A2 1.00TYP D 0.95TYP A3 0.8TYP D1 0.33 0.73 B 7.60 8.20 R1 0.2TYP B1 5.90 6.10 R2 0.2TYP B2 θ1 8 TYP C 2.20 θ2 10 TYP C1 1.70 1.90 θ3 4 TYP C2 0.15 0.30 θ4 5 TYP 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 21
Package Outline Dimension TSSOP24 Unit: mm 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 22
Package Outline Dimension QFN32 0.25 C TOP VIEW D 32 25 BOTTOM VIEW D2 25 32 1 24 24 1 e 17 8 L E E2 8 17 0.25 C 9 16 16 9 e b 0.10 M CAB 0.10 C SEATING PLANE A3 A1 A y C SYMBOL DIMENSION (mm) DIMENSION (MIL) MIN. NOM. MAX. MIN. NOM. MAX. A 0.70 0.75 0.80 27.6 29.5 31.5 A1 0 0.02 0.05 0 0.79 1.97 A3 0.25 REF 9.84 REF b 0.18 0.23 0.30 7.09 9.06 11.81 D 5.00 BSC 196.85 BSC D2 1.25 2.70 3.25 49.21 106.30 127.95 E 5.00 BSC 196.85 BSC E2 1.25 2.70 3.25 49.21 106.30 127.95 e 0.50 BSC 19.69 BSC L 0.30 0.40 0.50 11.81 15.75 19.69 y 0.10 3.94 Note: 1.DIMENSIONING AND TOLERANCING CONFORM TO ASME Y145.5M-1994. 2. REFER TO JEDEC STD. MO-220 WHHD-2 ISSUE A 16-bit Constant Current LED Driver with Error Detection Version:PRE.001 Page 23
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