The automotive industry is well along into the process of replacing incandescent lamps with lighting for headlights and turn signals based on LED technology. LEDs are often connected in series, which has created a need to ensure that a single LED dropout doesn’t cause a complete device failure.
The 6ZXTP56060FDBQ and the ZXTP56020FDBQ, recently announced by Diodes Incorporated, are PNP transistors designed to form the basis of the LED shunts that are often tasked to this purpose.
What Are LED Shunts?
In the diagram below, we see four LEDs connected in series, in a manner typical of automotive usage. Each LED is “shunted” by a PNP MOSFET, which is controlled by the matrix controller.
LED shunt. Image used courtesy of Diodes Incorporated
In the event that any of the four LEDs fail, the matrix controller directs its transistor shunt to turn on in a manner as to take the individual LED’s place, shunting the current around the non-operational LED.
|Test Conditions||ZXTP56020FDBQ VCE(SAT)||ZXTP56060FDBQ VCE(SAT)|
|IC = -500mA, IB = -50mA||-110 mV||-120 mV|
|IC = -1A, IB = -50mA||-220 mV||-250 mV|
|IC = -0.7A, IB = -7mA||-200 mV||-420 mV|
|IC = -2A, IB = -200mA||-390 mV||-450 mV|
Maximum collector-emitter saturation voltages (VCE(SAT))
Thus, unlike the classical Christmas tree light string, a single failure doesn’t mean that it’s “lights out”.
Absolute Maximum Specifications for Both Devices
The ZXTP56060FDBQ and the ZXTP56020FDBQ both come in packages of two transistors. As indicated by the shading in the diagram, two units can shunt four LEDs.
Maximum emitter-base voltage is -7 volts. Continuous and peak collector currents are -2 and -3 amps, respectively. Base current and peak base current are 0.3 and 1 amps, respectively.
Both devices offer a maximum power dissipation of 2.47 watts. Derating, as illustrated below, depends on operational conditions described in the datasheet.
Power dissipation deratings. Image used courtesy of Diodes Incorporated
As noted above, the ZXTP56020FDBQ features a maximum VCE(SAT) of 200 mV at an LED current (IC) of 700 mA. This serves to minimizes both power dissipation and operating temperature for improved lifetime and system reliability.
The ZXTP56020FDBQ offers typical turn on, delay, and rise times of 60, 10, and 50 ns, respectively. The equivalent figures for the ZXTP56060FDBQ are 90, 10, and 80ns.
The equivalent ON resistance (RCE(SAT)) for the ZXTP56020FDBQ and the ZXTP56060FDBQ are 220 and 250 mΩ, respectively.
Physical and Environmental Specifications
Both units are manufactured in IATF 16949-certified facilities. They are fully AEC-Q101 qualified and are both compatible with the Automotive Industry Action Group’s Production Part Approval Process (PPAP).
The bottom view (left), device symbol (middle), and top-view pinout (right) of the 60V ZXTP56060FDBQ and 20V ZXTP56020FDBQ. Image used courtesy of Diodes Incorporated
Both devices operate over a wide -55 to +150°C temperature range and are available in 2 x 2 x 0.6 mm DFN2020 packages.
Around the Industry
For those of you looking to weigh your options, there are a few comparable products available.
- ON Semiconductor’s NUD4700 is a complete two-terminal device that automatically resets itself if the LED heals itself or if it is replaced. It is aimed at use with automotive headlights.
- Bourns’ LSPxAJR series LED shunt protectors are a series of four complete units that operate at 6, 9, 13, and 18 volts.