MIC2845/6 6 Channel High Side Current Source WLED driver with Dual Low IQ LDOs General Description Features The MIC2845 and MIC2846 are all-in-one integrated circuits designed for driving White LEDs (WLEDs) for display backlighting, camera flash, and other modules in mobile devices. The MIC2845/6 uses 6 channels of current sinks to maintain constant current for up to 6 WLEDs. It features a typical dropout of less than 50mV at 20mA and guarantees less than 100mV over all conditions, thus allowing the WLEDs to be driven directly from the battery without the use of extra capacitors in a large and costly charge pump. The current sinks are accurate up to 95% while the matching between each channel is guaranteed above 96.5% at room temperature. The superior matching of MIC2845/6 insures clear and uniform display brightness under all conditions. The brightness of WLEDs is be externally preset by a resistor or internally programmed using pulse width modulation (PWM) on the MIC2845 or single-wire digital control on the MIC2846. The PWM brightness control on the MIC2845 will operate down to less than 1% duty cycle for an accurate and a high dynamic brightness range. The MIC2846 dimming features a single-wire digital interface which takes commands from digital programming pulses to change the brightness in a logarithmic scale similar to the eye’s perception of brightness. The single-wire digital brightness control is divided into two modes of operation for full brightness mode or battery saving mode for a total of 32 total brightness steps. The MIC2845/6 also features two independently enabled low quiescent current LDOs. Each LDO offers ±3% accuracy from the nominal voltage over temperature, low dropout voltage (150mV @ 150mA), and low ground current at all load conditions (typically 25µA). Both LDOs can be turned off to draw virtually no current. The MIC2845/6 are both available in the 2.5mm x 2.5mm 14-pin Thin MLF® leadless package with a junction temperature range of -40°C to +125°C. Datasheets and support documentation can be found on Micrel’s web site at: www.micrel.com. • Input voltage range: 3.0V to 5.5V WLED Driver • Current source dropout of less than 50mV guaranteed at 20mA • Accuracy better than ±95% (-40°C to +125°C) • Mismatching lower than ±3.5% (20°C) • Maintains proper regulation regardless of how many channels are utilized • Flash LED driver paralleling 6 channels • Two methods of dimming control – MIC2845 – PWM operation to <1% duty cycle – MIC2846 – Single wire digital control LDOs • • • • Very low ground current – <25µA each @ 150mA Stable with 1µF ceramic output capacitor Dropout at 150mV at 150mA Thermal shutdown and current limit protection Applications • Mobile handsets • Digital cameras • Portable media/MP3 players • Portable navigation devices (GPS) • Portable applications MLF and MicroLeadFrame are registered trademark Amkor Technology Inc. Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com January 2008 M9999-010808-A Micrel Inc. MIC2845/46 Typical Application Ordering Information LDO1 Output Voltage LDO2 Output Voltage Mark Code Temperature Range Package MIC2845-MFYMT 2.8V 1.5V YNMF –40°C to +125°C 14-Pin 2.5x2.5 MLF® MIC2845-MGYMT 2.8V 1.8V YNMG –40°C to +125°C 14-Pin 2.5x2.5 MLF® MIC2846-MFYMT 2.8V 1.5V YPMF –40°C to +125°C 14-Pin 2.5x2.5 MLF® MIC2846-MGYMT 2.8V 1.8V YPMG –40°C to +125°C 14-Pin 2.5x2.5 MLF® Part Number Note: 1. Output voltage range of each LDO is 1.0V to 3.3V in 50mV steps. Contact Micrel Marketing for other voltage options. Pin Configuration January 2008 MIC2845 MIC2846 2.5mm x 2.5mm Thin MLF® (Top View) 2.5mm x 2.5mm Thin MLF® (Top View) 2 M9999-010808-A Micrel Inc. MIC2845/46 Pin Description Pin Number MIC2845 Pin Number MIC2846 Pin Name 1 1 VIN 2 2 LDO2 3 3 EN2 Enable Input for LDO2. Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. 4 - END Enable high side current source. This pin can be used as a PWM input for dimming of WLEDs. Do not leave floating. - 4 DC Digital control input for high side current source. See Digital Dimming Interface. Do not leave floating. 5 5 RSET An internal 1.27V reference sets the nominal maximum WLED current. Example, apply a 20.5kΩ resistor between RSET and GND to set LED current to 20mA at 100% duty cycle. 6 6 D1 LED1 current sink input. Connect LED anode to VIN and cathode to this pin. 7 7 D2 LED2 current sink input. Connect LED anode to VIN and cathode to this pin. 8 8 D3 LED3 current sink input. Connect LED anode to VIN and cathode to this pin. Pin Function Voltage Input. Connect at least 1µF ceramic capacitor between VIN and GND. Output of LDO2. Connect at least 1µF ceramic output capacitor. 9 9 GND 10 10 D4 LED4 current sink input. Connect LED anode to VIN and cathode to this pin. 11 11 D5 LED5 current sink input. Connect LED anode to VIN and cathode to this pin. 12 12 D6 LED6 current sink input. Connect LED anode to VIN and cathode to this pin. 13 13 EN1 14 14 LDO1 January 2008 Ground. Enable Input for LDO1. Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. Output of LDO1. Connect a 1µF ceramic output capacitor. 3 M9999-010808-A Micrel Inc. MIC2845/46 Absolute Maximum Ratings(1) Operating Ratings(2) Main Input Voltage (VIN) ................................... -0.3V to +6V Enable/DC Input Voltage ................................. -0.3V to +6V Current Source Voltage ………………………...-0.3V to +6V Power Dissipation………………………..Internally Limited(3) Lead Temperature (soldering, 10sec.)....................... 260°C Storage Temperature (Ts) ..........................-65°C to +150°C ESD Rating(4) .................................................................. 2kV Supply Voltage (VIN)..................................... +3.0V to +5.5V Enable Input Voltage (VEN1/2,VDC,VEND) ................. 0V to VIN Current Source Voltage (VD1-6) .............................. 0V to VIN Junction Temperature (TJ) ........................ –40°C to +125°C Junction Thermal Resistance MLF® (θJA)..........................................................60°C/W Electrical Characteristics Linear Regulators VIN = VEN1 = VEN2 = 3.8V, VDC (2846) VEND (2845) = 0V; COUT1/2 = 2.2µF, IOUT1/2 = 100µA; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted. Parameter Conditions Output Voltage Accuracy Variation from nominal VOUT Min Typ Max Units +2 +3 % % 0.02 0.3 %/V 6 10 mV -2 -3 VIN Line Regulation Load Regulation IOUT = 100μA to 150mA Dropout Voltage VOUT > = 3.0V; IOUT = 150mA 150 330 mV Ground Pin Current IOUT = 100μA to 150mA 25 40 µA Ground Pin Current in Shutdown VEN < 0.2V, TJ < 85C 0.05 1.0 µA Ripple Rejection f = up to 1kHz; COUT = 2.2μF Current Limit VOUT = 0V Output Voltage Noise COUT = 2.2μF, 10Hz to 100kHz 65 200 300 dB 550 58 mA VRMS Enable Inputs (EN1, 2) Enable Input Voltage Logic Low 0.2 Logic High 1.2 Enable Hysterisis V 25 Enable Input Current VEN1/2 > 1.0V Turn-on Time COUT = 2.2µF; 90% of VOUT V mV 0.01 1 µA 50 100 µs Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. The maximum allowable power dissipation of any TA (ambient temperature) is PD(max) = TJ(max) – TA) / θJA. Exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. 4. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5kΩ in series with 100pF. January 2008 4 M9999-010808-A Micrel Inc. MIC2845/46 WLED Current Sinks VIN = VDC (2846) VEND (2845) = 3.8V, VEN1 = VEN2 = 0V; RSET = 20.5kΩ; VDROP = 0.6V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted. Parameter Conditions (5) Min Typ Max Units Current Accuracy VDROPNOM = 0.6V -5 +5 % Matching(6) VDROPNOM = 0.6V -3.6 -5.5 +3.6 +5.5 % % Drop-out Where ILED = 90% of LED current seen at VDROPNOM = 0.6V, 100% brightness level 50 100 mV Ground/Supply Bias Current IOUT = 20mA 1.0 Shutdown Current (current source leakage) VEND = 0V or VDC = 0V > 1260µs, VENLDO1,2 = 0V 0.01 mA 1 µA 0.2 V MIC2845- PWM Dimming Enable Input Voltage VEND Logic Low Logic High Enable Input Current 1.2 V VIH > 1.0V 0.01 10 µs Current Source Delay (50% levels) Shutdown to on(5) Standby to on; VDROP = 0.1V Standby to on; VDROP = 0.6V On to Standby; VDROP = 0.1V On to Standby; VDROP = 0.6V RSET = 20.5k 125 1 0.5 1 1 µs µs µs µs µs Current Source Transient Time (10%-90%) TRISE, VDROP = 0.1V TRISE, VDROP = 0.6V TFALL; VDROP = 0.1V TFALL, VDROP = 0.6V 1 1 0.3 0.3 µs µs µs µs Stand-by to shutdown time VEND = 0V Minimum Pulse Width 20 TBD 1 µA 40 ms 0.2 V MIC2846- Digital Dimming VDC Input Voltage VDC Logic Low Logic High 1.2 V VDC Enable Input Current VIH > 1.2V tSHUTDOWN Time DC pin is low to put into shutdown 1260 0.01 tMODE_UP Time DC pin is low to change to Count Up Mode 100 160 µs tMODE_DOWN Time DC pin is low to change to Count Down Mode 420 500 µs 32 tPROG_HIGH, tPROG_LOW Time for valid edge count; Ignored if outside limit range 1 tDELAY Time DC pin must remain high before a mode change can occur 140 tPROG_SETUP First down edge must occur in this window during presetting brightness 35 tSTART_UP Delay from DC is high to start up 140 1 µA µs µs µs 50 µs µs Notes: 5. As determined by average current of all channels in use and all channels loaded. 6. The current through each LED meet the stated limits from the average current of all LEDs. 7. Maximum differential in forward voltage anticipated from the LED with the highest forward voltage to the LED with the lowest forward voltage at nominal current. 8. Current accuracy guaranteed for VDROP current source 100mV to VIN-1.2V. 9. Dropout voltage is defined as the input-output differential at which the output voltage drops 2% below its nominal value measured at 1V differential. January 2008 5 M9999-010808-A Micrel Inc. MIC2845/46 Typical Characteristics (Current Sink) January 2008 6 M9999-010808-A Micrel Inc. MIC2845/46 Typical Characteristics (LDO) January 2008 7 M9999-010808-A Micrel Inc. MIC2845/46 Functional Characteristics (Current Sink) January 2008 8 M9999-010808-A Micrel Inc. MIC2845/46 Functional Characteristics (Current Sink) January 2008 9 M9999-010808-A Micrel Inc. MIC2845/46 Functional Characteristics (Current Sink) January 2008 10 M9999-010808-A Micrel Inc. MIC2845/46 Functional Diagram Figure 1. MIC2845 and MIC2846 Functional Block Diagram can reduce operating current down to 0.01µA in shutdown. Both linear regulators are stable with just 1µF of output capacitance. Functional Description The MIC2845/6 is a 6 channels WLED driver with dual 150mA LDOs. The WLED driver is designed to maintain proper current regulation with LED current accuracy of 95% while the minimum matching between the 6 channels to be 96.5% at room temperature. The WLEDs are driven independently from the input supply and will maintain regulation with a dropout of 50mV at 20mA. The low dropout of the current sinks allows the WLEDs to be driven directly from the input voltage and eliminates the need for large and inefficient charge pumps. If desired, multiple channels can be combined to drive a single WLED at a higher current for an intense light output. The combined method generates an extremely bright light suited for camera flash applications. The maximum WLED current for each channel is set via an external resistor. If dimming is desired the MIC2845 can dim via a PWM signal while the MIC2846 is controlled by a single-wire digital interface. Both dimming controls will be discussed in detail in the following sections. The MIC2845/6 has two LDOs with a dropout voltage of 150mV at 150mA and consume 25µA of current in operation. Each LDO has a dedicated enable pin, which January 2008 Block Diagram As shown in Figure 1, the MIC2845/6 consists of 2 LDOs and 6 current mirrors set to copy a master current determined by RSET. The current sinks have a designated control block for enabling and dimming of the WLEDs. The MIC2845 is controlled by the PWM control block that receives PWM signals for dimming. The MIC2846 dimming is controlled by an internal Digital Control Interface. The LDOs each have their own control block and are independent of the current sinks. In each LDO block, there are internal feedback resistors, an error amplifier, a PFET transistor and a control circuit for enabling. 11 M9999-010808-A Micrel Inc. MIC2845/46 VIN The input supply (VIN) provides power to the LDOs, the current sinks and the control circuitry. The VIN operating range is 3V to 5.5V. Due to wire inductance a minimum of 1µF/6.3V bypass capacitor should be placed close to input (VIN) pin and the ground (GND) pin. Refer to the layout recommendations section for details on placing the input capacitor (C1). LDO1/LDO2 The output pins for LDO one and LDO two are labeled LDO1 and LDO2, respectively. A minimum of 1µF bypass capacitor should be placed as close as possible to the output pin of each LDO. Refer to the layout recommendations section for details on placing the output capacitor (C2, C3) of the LDOs. Figure 2. Peak ILED vs. RSET EN1/EN2 A logic high signal on the enable pin activates the LDO output voltage of the device. A logic low signal on the enable pin deactivates the output and reduces supply current to 0.01µA. EN1 controls LDO1 and EN2 controls LDO2. MIC2845/6 LDOs feature built-in soft-start circuitry that reduces in-rush current and prevents the output voltage from overshooting at start up. Do not leave floating. D1-D6 The D1 through D6 pins are the current sink inputs for WLED 1 through 6, respectively. Connect the anodes of the WLEDs to VIN and each cathode of the WLEDs to D1 through D6. The current sinks are independent of each other. They can be used individually or combined. A single WLED can be driven with all 6 current sinks by connecting D1 through D6 together with the cathode of the WLED. This will generate a current 6 times ILED and can be used for higher current WLEDs such as those used in flash applications. The peak current of each current sink is 80mA at 100% duty cycle due to thermal limitations. With all 6 current sinks, the total current to drive a single flash WLED is 480mA. If the duty cycle is lowered to 10% of 1 second, a WLED can be driven over 1.5A by sinking 250mA on each channel, shown in Figure 3. END (MIC2845 Only) The END pin is equivalent to the enable pin for the current sinks on the MIC2845. It can also be used for dimming using a PWM signal. See the MIC2845 PWM Dimming Interface in the Application Information section for details. DC (MIC2846 Only) The DC pin is equivalent to the enable pin for the current sinks on the MIC2846. It can also be used for dimming using a single-wire digital interface. See the MIC2846 Digital Dimming Interface in the Application Information section for details. RSET The RSET pin is used by connecting a RSET resistor to ground to set the peak current of the current sinks. The average LED current can be calculated by the equation (1) below: ILED (mA) = 410 * D / RSET (kΩ) (1) D is the duty cycle of the LED current during PWM dimming (MIC2845) or single-wire digital dimming (MIC2846). When the device is fully on the duty cycle equals 100% (D = 1). A plot of ILED versus RSET at 100% duty cycle is shown in Figure 2. January 2008 Figure 3. Flash LED Driver Circuit GND The ground pin is the ground path for the current sinks as well as the LDOs. The current loop for the ground should be as small as possible. The ground of the input and output capacitors should be routed with low impedance traces to the GND pin and made as short as possible. Refer to the layout recommendations for more details. 12 M9999-010808-A Micrel Inc. MIC2845/46 Application Information MIC2845 PWM Dimming Interface The MIC2845 can receive PWM signals from the END pin for WLED dimming. The frequency of the PWM signal should be between 200Hz – 1kHz and the duty cycle can range from 1% to 100%. Dimming is generated by pulsing the WLEDs on and off in synchronization with the PWM signal. An internal shutdown delay ensures that the internal control circuitry remains active during PWM dimming for optimum performance. Figure 4 through Figure 8 show the WLED current response when a PWM signal is applied to the END pin. Figure 6. PWM Signal at 50% Duty Cycle Figure 4. PWM Signal at 1% Duty Cycle Figure 7. PWM Signal at 80% Duty Cycle Figure 5. PWM Signal at 20% Duty Cycle Figure 8. PWM Signal at 100% Duty Cycle January 2008 13 M9999-010808-A Micrel Inc. MIC2845/46 by design to mimic the sensitivity of the human eye. Refer to Table 1 for the translation from brightness level to LED duty cycle and current. The MIC2846 is designed to receive programming pulses to increase or decrease brightness. Once the brightness change signal is received, the DC pin is simply pulled high to maintain the brightness. This “set and forget” feature relieves processor computing power by eliminating the need to constantly send a PWM signal to the dimming pin. With a digital control interface, brightness levels can also be preset so that WLEDs can be turned on at any particular brightness level. MIC2846 Digital Dimming Interface The MIC2846 incorporates an easy to use single-wire, serial programming interface that allows users to set WLED brightness up to 32 different levels, as shown in Table 1. Level (0-31) LED Duty Cycle (%) Average ILED (mA) 0 100 12 1 86 10.32 2 72 8.6 3 59 7.1 4 45.5 5.5 5 36.5 4.4 6 29.5 3.5 7 22.5 2.7 8 18 2.2 9 13.5 1.6 10 9.5 1.1 11 8 0.96 12 6 0.72 13 5 0.6 IPEAK (mA) Start Up Assuming the MIC2846 has been off for a long time and no presetting brightness command is issued (presetting is discussed in a later section), the MIC2846 will start-up in its default mode approximately 140µs (tSTART_UP) after a logic level high is applied to the DC pin. In the default mode the WLEDs are turned on at the maximum brightness level of 31. Each falling edges during the tPROG_SETUP period will cause the default brightness level to decrease by one. This is discussed in more detail in the Presetting Brightness section. 60% of ILEDPEAK (12mA for RSET = 20.5k) 14 4 0.48 15 1.6 0.192 16 1.6 0.32 17 4 0.8 18 5 1 19 6 1.2 Figure 9. Typical Start-Up Timing 20 8 1.6 21 9.5 1.9 22 13.5 2.7 23 18 3.6 Shutdown Whenever the DC input pin is pulled low for a period greater than or equal to tSHUTDOWN(1260µs), the MIC2846 will be in shutdown, shown in Figure 10. 24 22.5 4.5 25 29.5 5.9 26 36.5 7.3 27 45.5 9.1 28 59 11.8 29 72 14.4 30 86 17.2 31 100 20 100% of ILEDPEAK (20mA for RSET = 20.5k) Figure 10. Shutdown Timing Once the device is shutdown, the control circuit supply is disabled and the WLEDs are turned off, drawing only 0.01µA. Brightness level information stored in the MIC2846 prior to shutdown will be erased. Table 1. Digital Interface Brightness Level Table Brightness levels 0-15 is logarithmically spaced with a peak current equal to 60% of the current set by RSET. Brightness levels 16-31 is also logarithmically spaced with a peak current equal to the current determined by RSET. Spacing between each level is in logarithmic scale January 2008 Count Up Mode/Count Down Mode The mode of MIC2846 can be in either Count Up Mode or Count Down Mode. The Counting Modes determine what the falling edges of the programming pulses will do 14 M9999-010808-A Micrel Inc. MIC2845/46 to the brightness. In Count Up Mode, subsequent falling edges will increase brightness while in Count Down Mode, subsequent falling edges will decrease brightness. By default, the MIC2846 is in Count Down Mode when first turned on. The counting mode can be changed to Count Up Mode, by pulling the DC pin low for a period equal to tMODE_UP (100µs to 160µs), shown in Figure 11. The device will remain in Count Up Mode until its mode is changed to Count Down Mode or by disabling the MIC2846 to reset the mode back to default. tPROG_LOW tPROG_HIGH DC LEVEL n + 1 LEVEL n LEVEL n - 1 BRIGHTNESS LEVEL PULSE IGNORED Figure 13. Brightness Programming Pulses Multiple brightness levels can be changed as shown in Figure 14. When issuing multiple brightness level adjustments to the DC pin, ensure both tPROG_LOW and tPROG_HIGH are within 1µs and 32µs. To maintain operation at the current brightness level simply maintain a logic level high at the DC pin. Figure 11. Mode Change to Count Up To change the mode back to Count Down Mode, pull the DC pin low for a period equal to tMODE_DOWN (420µs to 500µs), shown in Figure 12. Now the internal circuitry will remain in Count Down Mode until changed to Count Up as described previously. Figure 12. Mode Change to Count Down Figure 14. Decreasing Brightness Several Levels Programming the Brightness Level MIC2846 is designed to start driving the WLEDs 140µs (tSTART_UP) after the DC pin is first pulled high at the maximum brightness level of 31. After start up, the internal control logic is ready to decrease the WLED brightness upon receiving programming pulses (negative edges applied to DC pin). Since MIC2846 starts in Count Down Mode, the brightness level is decreased one level by applying two programming pulses, as shown in Figure 13. Note that the extra pulse is needed to decrease brightness because the first edge is ignored. Anytime the first falling edge happens greater than 32µs after a Mode Change, it will be ignored. Ignoring the first falling edge is necessary in order that Mode Change (tMODE_UP, tMODE_DOWN) pulses do not result in adjustments to the brightness level. Each programming pulse has a high (tPROG_HIGH) and a low (tPROG_LOW) pulse width that must be between 1µs to 32µs. The MIC2846 will remember the brightness level and mode it was changed to. For proper operation, ensure that the DC pin has remained high for at least tDELAY(140µs) before issuing a mode change command. January 2008 As mentioned, MIC2846 can be programmed to set WLED drive current to produce one of 32 distinct brightness levels. The internal logic keeps track of the brightness level with an Up/Down counter circuit. The following section explains how the brightness counter functions with continued programming edges. One-Step Brightness Changes The “One-Step” brightness change procedure relieves the user from keeping track of the MIC2846’s up/down counter mode. It combines a Mode Change with a programming edge; therefore, regardless of the previous Count Mode, it will change the brightness level by one. 15 M9999-010808-A Micrel Inc. MIC2845/46 Figure 15. One-Step Brightness Decrease Figure 17. Presetting Timing The One-Step Brightness Decrease method is quite simple. First, the DC pin is pulled low for a period equal to the tMODE_DOWN (420µs to 500µs) and immediately followed by a falling edge within tPROG_HIGH (1µs to 32µs) as shown in Figure 15. This will decrease the brightness level by 1. Similarly a One-Step Brightness Increase can be assured by first generating a DC down pulse whose period is equal to the tMODE_UP (100µs to 160µs) and immediately followed by a falling edge within tPROG_HIGH (1µs to 32µs). Figure 16 illustrates the proper timing for execution of a One-Step Brightness Increase. Figure 17 shows the correct presetting sequence to set the MIC2846 brightness to level 22 prior to start up. Notice that when using the presetting feature the first programming pulse is not ignored. This is because the counter’s default mode is Count Down and a Mode Change cannot be performed in the presetting mode. (Note that the tPROG_HIGH and tPROG_LOW pulse width must still be between 1µs to 32µs`.) Figure 16. One-Step Brightness Increase Presetting Brightness The MIC2846 does not turn on the current sinks until DC pin is kept high for tSTART_UP (140µs). This grants the user time to preset the brightness level by sending a series of programming edges via the DC pin. The precise timing for the first down edge is between 35µs to 50µs after the DC pin is first pulled high. The 15µs timeframe between 35µs and 50µs is the tPROG_SETUP period. The first presetting pulse edge must occur somewhere between the timeframe of 35µs to 50µs, otherwise the MIC2846 may continue to start up at the full (default) brightness level. January 2008 16 M9999-010808-A Micrel Inc. MIC2845/46 LDO Thermal Considerations The MIC2845/6 LDOs are each designed to provide 150mA of continuous current. Maximum ambient operating temperature can be calculated based on the output current and the voltage drop across the part. For example if the input voltage is 3.6V, the output voltage is 2.8V, and the output current = 150mA. The actual power dissipation of the regulator circuit can be determined using the equation: MIC2845/6 LDOs are low noise 150mA LDOs. The MIC2845/6 LDO regulator is fully protected from damage due to fault conditions, offering linear current limiting and thermal shutdown. Input Capacitor The MIC2845/6 LDOs are high-performance, high bandwidth devices. Stability can be maintained using a ceramic input capacitor of 1µF. Low-ESR ceramic capacitors provide optimal performance at a minimum amount of space. Additional high-frequency capacitors, such as small-valued NPO dielectric-type capacitors, help filter out high-frequency noise and are good practice in any noise sensitive circuit. X5R or X7R dielectrics are recommended for the input capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore, not recommended. PLDO1 = (VIN – VOUT1) I OUT + VIN IGND Because this device is CMOS and the ground current (IGND) is typically <100µA over the load range, the power dissipation contributed by the ground current is < 1% and can be ignored for this calculation. PLDO1 = (3.6V – 2.8V) x 150mA PLDO1 = 0.120W Since there are two LDOs in the same package, the power dissipation must be calculated individually and then summed together to arrive at the total power dissipation. PTOTAL = PLDO1 + PLDO2 Output Capacitor The MIC2845/6 LDOs require an output capacitor of at least 1µF or greater to maintain stability, however, the output capacitor can be increased to 2.2µF to reduce output noise without increasing package size. The design is optimized for use with low-ESR ceramic chip capacitors. High ESR capacitors are not recommended because they may cause high frequency oscillation. X7R/X5R dielectric-type ceramic capacitors are recommended due to their improved temperature performance compared to Z5U and Y5V capacitors. X7R-type capacitors change capacitance by 15% over their operating temperature range and are the most stable type of ceramic capacitors. Z5U and Y5V dielectric capacitors change value by as much as 50% and 60%, respectively, over their operating temperature ranges. To use a ceramic chip capacitor with Y5V dielectric, the value must be much higher than an X7R ceramic capacitor to ensure the same minimum capacitance over the equivalent operating temperature range. To determine the maximum ambient operating temperature of the package, use the junction-to-ambient thermal resistance (θJA = 60°C/W) of the device and the following basic equation: ⎛ TJ(max) − TA PTOTAL(max) = ⎜⎜ θ JA ⎝ TJ(max) = 125°C, is the maximum junction temperature of the die and θJA, is the thermal resistance = 60°C/W. Substituting PTOTAL for PTOTAL(max) and solving for the ambient operating temperature will give the maximum operating conditions for the regulator circuit. For example, when operating the MIC2845/6 LDOs (LDO1 = 2.8V and LDO2 = 1.5V) at an input voltage of 3.6V with 150mA load on each, the maximum ambient operating temperature TA can be determined as follows: PLDO1 = (3.6V – 2.8V) x 150mA = 0.120W PLDO2 = (3.6V – 1.5V) x 150mA = 0.315W PTOTAL=0.120W+ 0.315W = 0.435W = (125°C – TA)/(60°C/W) TA = 125°C – 0.435W x 60°C/W TA = 98.9°C Therefore, under the above conditions, the maximum ambient operating temperature of 98.9°C is allowed. No-Load Stability Unlike many other voltage regulators, the MIC2845/6 LDOs will remain stable and in regulation with no load. This is especially important in CMOS RAM keep-alive applications. January 2008 ⎞ ⎟⎟ ⎠ 17 M9999-010808-A Micrel Inc. MIC2845/46 MIC2845 Typical Application Circuit Bill of Materials Item Part Number C1, C2, C3 C1608X5R0J105K R1 U1 CRCW06032052FT1 MIC2845-xxYMT Manufacturer TDK(1) (2) Vishay Micrel, Inc. (3) Description Qty. 1µF Ceramic Capacitor, 6.3V, X5R, Size 0603 3 20.5kΩ, 1%, Size 0603 1 6 Channel PWM Controlled Current Sink WLED Driver with Dual LDOs 1 Notes: 1. TDK: www.tdk.com 2. Vishay: www.vishay.com 5. Micrel, Inc.: www.micrel.com January 2008 18 M9999-010808-A Micrel Inc. MIC2845/46 MIC2846 Typical Application Circuit Bill of Materials Item Part Number C1, C2, C3 C1608X5R0J105K R1 U1 CRCW06032052FT1 MIC2846-xxYMT Manufacturer TDK(1) (2) Vishay Micrel, Inc. (3) Description Qty. 1µF Ceramic Capacitor, 6.3V, X5R, Size 0603 3 20.5kΩ, 1%, Size 0603 1 6 Channel Digital Controlled Current Sink WLED Driver with Dual LDOs 1 Notes: 1. TDK: www.tdk.com 2. Vishay: www.vishay.com 5. Micrel, Inc.: www.micrel.com January 2008 19 M9999-010808-A Micrel Inc. MIC2845/46 PCB Layout Recommendations (Fixed) Top Layer Fixed Bottom Layer January 2008 20 M9999-010808-A Micrel Inc. MIC2845/46 Package Information 14-Pin (2.5mm x 2.5mm) Thin MLF® (MT) MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2008 Micrel, Incorporated. January 2008 21 M9999-010808-A