The LM3414 and LM3414HV are 1-A 60-W(1) common anode-capable constant current buck LED drivers. They are suitable for driving single string of 3-W HBLED with up to 96% efficiency. They accept input voltages from 4.5 VDC to 65 VDC and deliver up to 1-A average LED current with ±3% accuracy. The integrated low-side N-channel power MOSFET and current sensing element realize simple and low component count circuitry, as no bootstrapping capacitor and external current-sensing resistor are required. An external small-signal resistor to ground provides very fine LED current adjustment, analog dimming, and thermal fold-back functions.
Constant switching frequency operation eases EMI. No external loop compensation network is needed. The proprietary Pulse-Level-Modulation (PLM) control method benefits in high conversion efficiency and true average LED current regulation. Fast response time realizes fine LED current pulse fulfilling the 240 Hz 256-step dimming resolution requirement for general lighting.
The LM3414 and LM3414HV are available in SOIC-8 and 3 mm × 3 mm WSON-8 packages.
PART NUMBER | PACKAGE | BODY SIZE (NOM) |
---|---|---|
LM3414, LM3414HV |
WSON (8) | 3.00 mm × 3.00 mm |
SOIC (8) | 3.90 mm × 4.89 mm |
Changes from E Revision (May 2013) to F Revision
Changes from D Revision (April 2013) to E Revision
PIN | I/O | DESCRIPTION | |
---|---|---|---|
NAME | NO. | ||
VCC | 1 | O | Internal Regulator Output Pin. This pin should be bypassed to ground by a ceramic capacitor with a minimum value of 1 µF. |
PGND | 2 | — | Power Ground Pin. Ground for power circuitry. Reference point for all stated voltages. Must be externally connected to EP and GND. |
IADJ | 3 | I | Average Output Current Adjustment Pin. Connect resistor RIADJ from this pin to ground to adjust the average output current. |
GND | 4 | — | Analog Ground Pin. Analog ground connection for internal circuitry, must be connected to PGND external to the package. |
FS | 5 | I | Switching Frequency Setting Pin. Connect resistor RFS from this pin to ground to set the switching frequency. |
DIM | 6 | I | PWM Dimming Control Pin. Apply logic level PWM signal to this pin controls the intend brightness of the LED string. |
LX | 7 | O | Drain of N-MOSFET Switch. Connect this pin to the output inductor and anode of the schottky diode. |
VIN | 8 | I | Input Voltage Pin. The input voltage should be in the range of 4.5 V to 42 V (LM3414) or 4.5 V to 65 V (LM3414HV). |
EP | EP | — | Thermal Pad (Power Ground). Used to dissipate heat from the package during operation. Must be electrically connected to PGND external to the package. |
MIN | MAX | UNIT | ||
---|---|---|---|---|
VIN to GND | LM3414 | –0.3 | 42 | V |
LM3414HV | –0.3 | 65 | ||
VIN to GND (Transient) | LM3414 | 45 (500 ms) | V | |
LM3414HV | 67 (500 ms) | |||
LX to PGND | LM3414 | –0.3 | 42 | V |
LM3414HV | –0.3 | 65 | ||
LX to PGND (Transient) | LM3414 | –3 (2 ns) | 45 (500 ms) | V |
LM3414HV | –3 (2 ns) | 67 (500 ms) | ||
FS, IADJ to GND | –0.3 | 5 | V | |
DIM to GND | –0.3 | 6 | V | |
Storage Temperature | –65 | 125 | °C |
VALUE | UNIT | |||
---|---|---|---|---|
WSON PACKAGE | ||||
V(ESD) | Electrostatic discharge | Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)(3) | ±2000 | V |
Charged-device model (CDM), per JEDEC specification JESD22-C101(2) | ±750 | |||
SOIC PACKAGE | ||||
V(ESD) | Electrostatic discharge | Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)(3) | ±2000 | V |
Charged-device model (CDM), per JEDEC specification JESD22-C101(2) | ±750 |
MIN | NOM | MAX | UNIT | ||
---|---|---|---|---|---|
VIN | LM3414 | 4.5 | 42 | V | |
LM3414HV | 4.5 | 65 | |||
Junction temperature | –40 | 125 | °C |
THERMAL METRIC(1) | LM3414, LM3414HV | UNIT | ||
---|---|---|---|---|
NGQ (WSON) | DDA (SOIC-8) | |||
8 PINS | 8 PINS | |||
RθJA | Junction-to-ambient thermal resistance | 47.7 | 50.5 | °C/W |
RθJC(top) | Junction-to-case (top) thermal resistance | 43.1 | 55.7 | °C/W |
RθJB | Junction-to-board thermal resistance | 22.3 | 28.6 | °C/W |
ψJT | Junction-to-top characterization parameter | 0.4 | 9.5 | °C/W |
ψJB | Junction-to-board characterization parameter | 22.5 | 28.5 | °C/W |
RθJC(bot) | Junction-to-case (bottom) thermal resistance | 4 | 3.2 | °C/W |
PARAMETER | TEST CONDITIONS | MIN(1) | TYP(2) | MAX(1) | UNIT | |
---|---|---|---|---|---|---|
SYSTEM PARAMETERS - LM3414 | ||||||
IIN-DIM-HIGH | Operating Current | 4.5 V ≤ Vin ≤ 42 V RIADJ = 3.125 kΩ VDIM = High |
2.2 | 3.2 | 3.5 | mA |
IIN-DIM-LOW | Standby Current | 4.5 V ≤ Vin ≤ 42 V RIADJ = 3.125 kΩ VDIM = Low |
0.8 | 1.15 | 1.4 | mA |
ILX-OFF | LX Pin Current | Main Switch Turned OFF VLX = VIN = 42 V |
6 | µA | ||
SYSTEM PARAMETERS - LM3414HV | ||||||
IIN-DIM-HIGH | Operating Current | 4.5 V ≤ Vin ≤ 65 V RIADJ = 3.125 kΩ VDIM = High |
2.2 | 3.3 | 3.6 | mA |
IIN-DIM-LOW | Standby Current | 4.5 V ≤ Vin ≤ 65 V RIADJ = 3.125 kΩ VDIM = Low |
0.8 | 1.2 | 1.45 | mA |
ILX-OFF | LX Pin Current | Main Switch Turned OFF VLX = VIN= 65 V |
6.5 | µA | ||
SYSTEM PARAMETERS - LM3414/3414HV | ||||||
ILED | Average LED Current | RIADJ = 3.125 kΩ TA = 25°C |
0.97 | 1 | 1.03 | A |
RIADJ = 3.125 kΩ TA = –40°C to 125°C |
0.95 | 1 | 1.05 | A | ||
VCC-UVLO | Vcc UVLO Threshold | VCC Decreasing, TA = 25°C | 3.6 | 3.75 | 3.9 | V |
VCC-UVLO-HYS | Vcc UVLO Hysteresis | 300 | mV | |||
VIADJ | IADJ Pin voltage | 1.23 | 1.255 | 1.280 | V | |
VDIM | DIM Pin Threshold | VDIM Increasing | 1 | 1.2 | V | |
VDIM-HYS | DIM Pin Hysteresis | 100 | mV | |||
fSW | Switching frequency | 250 | 500 | 1000 | kHz | |
fSW-TOL | Switching frequency tolerance | RFS = 40 kΩ | 420 | 500 | 580 | kHz |
tON-MIN | Minimum on-time | 400 | ns | |||
INTERNAL VOLTAGE REGULATOR | ||||||
VCC | VCC regulator output voltage(3) | CVCC = 1 µF, No Load to IVCC = 2 mA | 4.7 | 5.4 | 6 | V |
VIN = 4.5 V, 2-mA Load | 3.8 | 4.2 | V | |||
MAIN SWITCH | ||||||
RLX | Resistance across LX and GND | Main Switch Turned ON | 1.8 | Ω | ||
THERMAL PROTECTION | ||||||
TSD | Thermal shutdown temperature | TJ Rising | 170 | °C | ||
TSD-HYS | Thermal shutdown temperature hysteresis | TJ Falling | 10 | °C |
The LM3414/HV is a high power floating buck LED driver with wide input voltage ranges. The device requires no external current sensing elements and loop compensation networks. The integrated power N-MOSFET enables high-output power with up to 1000-mA output current. The combination of Pulse Width Modulation (PWM), control architecture, and the proprietary Pulse Level Modulation (PLM) ensures accurate current regulation, good EMI performance, and provides high flexibility on inductor selection. High-speed dimming control input allows precision and high resolution brightness control for applications require fine brightness adjustment.
The main control circuitry of the LM3414/HV is generally a Pulse-Width-Modulated (PWM) controller with the incorporation of the Pulse-Level-Modulation (PLM) technology. PLM is a technology that facilitates true output average current control without the need to sense the output current directly. In the LM3414/LM3414HV, the PLM circuit senses the current of the internal switch through integrated current sensing circuitry to realize average output current control. The use of PLM reduces the current sensing power losses as it needs current information only when the switch is turned ON. For proper operation of this control scheme, the converter must operate in CCM (continuous conduction mode), so the switching frequency and inductor value must be chosen to prevent the inductor current reaching 0 A during the switch OFF time each cycle.
In general, for the LED drivers with current sensing resistor at the output, the power dissipation on the current sensing resistor is ILED2 × RISNS, where ILED is the average output current and RISNS is the resistance of the current sensing resistor. In the LM3414/LM3414HV, power dissipates on the internal RISNS only during ON period of the internal power switch. The power loss on RISNS(internal) becomes ILED2 × RISNS × D, where D is the switching duty cycle. For example, when the switching duty cycle, D of a converter is 0.5, the power loss on RISNS with PLM is half of those with conventional output current sensing resulting in increased efficiency.
The Pulse-Level-Modulation is a patented method to ensure accurate average output current regulation without the need of direct output current sensing. Figure 14 shows the current waveforms of a typical buck converter under steady state, where, IL1 is the inductor current and ILX is the main switch current flowing into the LX pin. For a buck converter operating in steady state, the mid-point of the RAMP section of the main switch current is equal to the average level of the inductor current–hence the average output current. In short, by regulating the mid-point of the RAMP section of the main switch current with respect to a precise reference level, PLM achieves output current regulation by sensing the main switch current solely.
As the LM3414 features a 400 ns minimum ON time, it is essential to make sure the ON time of the internal switch is not shorter than 400 ns when setting the LED driving current. If the switching ON time is shorter than 400 ns, the accuracy of the LED current may not maintain and exceed the rated current of the LEDs. The ratio of the LED forward voltage to input voltage is restricted by the following restriction, as shown in Equation 1.
The LM3414/HV features an integrated switch current limiting mechanism that protects the LEDs from being overdriven. The switch current limiter triggers when the switch current exceeds three times the current level set by RIADJ. Once the current limiter is triggered, the internal power switch turns OFF for 3.6 µs to allow the inductor to discharge and cycles repetitively until the overcurrent condition is removed. The current limiting feature is exceptionally important to avoid permanent damage of the LM3414/HV application circuit due to short circuit of LED string.
The DIM pin of the LM3414/HV is an input with internal pullup that accepts logic signals for average LED current control. Applying a logic high (greater than 1.2 V) signal to the DIM pin or leaving the DIM pin open will enable the device. Applying a logic low signal (less than 0.9 V) to the DIM pin will disable the switching activity of the device but maintain VCC regulator active. The LM3414/HV allows the inductor current to slew up to the preset regulated level at full speed instead of charging the inductor with multiple restrained switching duty cycles. This enables the LM3414/HV to achieve high-speed dimming and very fine dimming control as shown in Figure 15 and Figure 16.
To ensure normal operation of the LM3414/HV, TI recommends setting the dimming frequency not higher than 1/10 of the switching frequency. The minimum dimming duty cycle is limited by the 400 ns minimum ON time. In applications that require high dimming contrast ratio, low dimming frequency should be used.
The IADJ pin can be used as an analog dimming signal input. As the average output current of the LM3414 depends on the current being drawn from the IADJ pin, thus the LED current can be increased or decreased by applying external bias current to the IADJ pin. The simplified circuit diagram for facilitating analog dimming is as shown in Figure 17. The minimum LED current for analog dimming is 100 mA and the converter must remain in continuous conduction mode (CCM). The switching frequency and inductor value must be sized accordingly.
When external bias current IEXT is applied to the IADJ pin, the reduction of LED current follows Equation 2 through Equation 3.
Provided that
ILED decreases linearly as IEXT increases.
This feature is exceptionally useful for the applications with analog dimming control signals such as those from analog temperature sensors and ambient light sensors.
Figure 18 shows an example circuit for analog dimming control using simple external biasing circuitry with a variable resistor.
In Figure 18, the variable resistor VR1 controls the base voltage of Q1 and eventually adjusts the bias voltage of current to the IADJ pin (IEXT). As the resistance of VR1 increases and the voltage across VR1 exceeds 1.255 V + 0.7 V, the LED current starts to decrease as IEXT increases.
Where
The analog dimming begins only when IEXT > 0.
The LM3414/HV features a 5.4-V internal voltage regulator that connects between the VIN and VCC pins for powering internal circuitry and provide biases to external components. The VCC pin must be bypassed to the GND pin with a 1-µF ceramic capacitor, CVCC that connected to the pins as close as possible. When the input voltage falls to less than 6 V, the VCC voltage will drop to less than 5.4 V and decrease proportionally as Vin decreases. The device will shutdown as the VCC voltage falls to less than 3.9 V. When the internal regulator is used to provide bias to external circuitry, it is essential to ensure the current sinks from VCC pin does not exceed 2 mA to maintain correct voltage regulation.
There are no additional functional modes for this device.