XR76208-Q

AEC-Q100 Qualified 40V, 8A Synchronous Step-Down COT Regulator

Description

The XR76208-Q is a synchronous step-down regulator combining the controller, drivers, bootstrap diode and MOSFETs in a single package for point-of-load supplies well suited for automotive applications. Qualified per AEC-Q100, the XR76208-Q has a load current rating of 8A. A wide 5.5V to 40V input voltage range allows for single supply operation from industry standard 24V ±10%, 18V-36V, and rectified 18VAC and 24VAC rails.

With a proprietary emulated current mode Constant On-Time (COT) control scheme, the XR76208-Q provides extremely fast line and load transient response using ceramic output capacitors. It requires no loop compensation, simplifying circuit implementation and reducing overall component count. The control loop also provides 0.07% load and 0.15% line regulation and maintains constant operating frequency. A selectable power saving mode allows the user to operate in Discontinuous Conduction Mode (DCM) at light current loads thereby significantly increasing the converter efficiency.

A host of protection features, including overcurrent, over temperature, short-circuit and UVLO, helps achieve safe operation under abnormal operating conditions.

The XR76208-Q is available in a RoHS-compliant, green/halogen-free space-saving QFN 5 x 5mm package.

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Features

  • Automotive AEC-Q100 Qualified
    • Temperature Grade1: -40°C to 125°C
    • HBM ESD Class Level 2
    • CDM ESD Class Level C4B
  • Controller, drivers, bootstrap diode and MOSFETs integrated in one package
  • 8A step-down regulator
    • Wide 5.5V to 40V input voltage range
    • ≥0.6V adjustable output voltage
  • Proprietary constant on-time control
    • No loop compensation required
    • Stable ceramic output capacitor operation
    • Programmable 200ns to 2µs on-time
    • Constant 100kHz to 800kHz frequency
  • Selectable CCM or CCM/DCM
    • CCM/DCM for high efficiency at light load
    • CCM for constant frequency at light load
  • Programmable hiccup current limit with thermal compensation
  • Precision enable and power good flag
  • Programmable soft-start
  • 30-pin 5 x 5mm QFN package with wettable flanks
  • Pin compatible 5A regulator, XR76205-Q
  • Pin compatible 3A regulator, XR76203-Q

Application

  • Automotive systems
  • Distributed power architecture
  • Point-of-Load (POL) converters
  • Power supply modules
  • FPGA, DSP and processor supplies
  • Industrial and military applications
  • Base stations, switches/routers and servers

Design Tools

Packaging

Pkg Code Details Quantities Dimensions PDF
QFN30 5x5 OPT2
  • JEDEC Reference: MO-220
  • MSL Pb-Free: L1 @ 260ºC
  • MSL SnPb Eutectic:
  • ThetaJA: 29ºC/W
  • Bulk Pack Style: Tray
  • Quantity per Bulk Pack: 490
  • Quantity per Reel: 3000
  • Quantity per Tube: N/A
  • Quantity per Tray: 490
  • Reel Size (Dia. x Width x Pitch): 330 x 12 x 8
  • Tape & Reel Unit Orientation: Quadrant 1
  • Dimensions: mm
  • Length: 5
  • Width: 5
  • Thickness: 1.00
  • Lead Pitch: 0.5

Parts & Purchasing

Part Number Pkg Code RoHS Min Temp Max Temp Status Buy Now Order Samples
XR76208EL-Q QFN30 5x5 OPT2 -40 125 Active
XR76208ELTR-Q QFN30 5x5 OPT2 -40 125 Active
XR76208EVB-Q Board Active
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Part Status Legend
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PRE (Pre-introduction) - the part has not been introduced or the part number is an early version available for sample only.
OBS (Obsolete) - the part is no longer being manufactured and may not be ordered.
NRND (Not Recommended for New Designs) - the part is not recommended for new designs.
Distribution Date Description File

Frequently Asked Questions

Voltage mode PWM

Voltage mode PWM is a simple technique that uses a single loop to control the output voltage. As shown in Figure 1, the output voltage is compared to a reference voltage with an error amplifier. The output of the error amplifier is then compared to a sawtooth and that output is used to drive the MOSFET, usually via a voltage divider.

 


Figure 1

 

As shown in Figure 2, the output voltage is modulated by turning the high-side FET on (on-time) with the pulse width and turning the low side FET off. At the end of the pulse, the high-side FET is turned off (off-time) and the low side FET is turned on until the next pulse. Vout = On-Time/Period * Vin.

 

Figure 2
 

The advantages of voltage mode PWM is that it is a very simple, common, smaller solution with good accuracy. The disadvantages are that complex frequency compensation is required (two poles) to stabilize the loop and because trailing edge control is most commonly used, there is a delay in load step response.

Current mode PWM

With voltage mode PWM, current is less known. For better control, current mode PWM senses the inductor current and it is compared to the reference voltage as shown in Figure 3.

 


Figure 3

 

Although the current has to be sensed with accuracy and introduces noise, the advantages of current mode PWM are easier loop compensation (less compensation needed with one pole), and it is easier to implement over-current protection and parallel currents to the output.

Standard Constant On-Time (COT)

As opposed to PWM, the pulse width in COT is always the same as shown in Figure 4. Instead the off-time length varies (as does the frequency) which modulates the output. As the Vout increases, the off-time of the duty cycle increases (frequency decreases) and the fixed on-time produces a lower duty cycle. This transfers less energy to the output and lowers the Vout. More simply said, as Vout increases, the duty cycle decreases. Conversely, as the Vout decreases, the off-time of the duty cycle decreases (frequency increases) and the fixed on-time produces a higher duty cycle. This transfers more energy to the output and raises the Vout.

 


Figure 4

 

The advantages of standard COT are very fast transient response, simplicity (inexpensive) and that frequency compensation is not complex as it is in PWM control. However, the feedback signal tends to have low amplitude and signal to noise ratio, making it very noise sensitive. Also, the output voltage is higher than the reference voltage and the ripple is dependent on and sensitive to the output capacitor ESR. This introduces a DC offset which is the average amount the output voltage is over the reference voltage. It is also jitter prone and the frequency changes during the load steps.

Some solutions solve the noise sensitivity by having one of two options that condition the feedback signal but introduce delays. One tradeoff provides faster transient responses; the other allows low ESR output capacitors to be used.

MaxLinear’s patented COT

MaxLinear’s patented COT architecture however conditions the reference instead as shown in Figure 5. The MaxLinear devices create their own emulated ramp that is insensitive to noise and the ESR of the capacitor. Since the output capacitor ESR does not affect it, low ESR ceramic capacitors can be used and maintain stability without decreasing speed. In addition, the Vout and reference voltage are compared and that result controls the ramp circuit. This creates a slower loop where the output voltage is averaged out and the DC offset is not introduced as in standard COT.

 


Figure 5

 

MaxLinear’s COT still has the standard COT advantages of very fast transient response, simplicity and no complex frequency compensation in addition to not having DC offset or ESR value sensitivity. MaxLinear’s COT architecture provides exceptional line and load regulation.

Find the product page of the part that you want to get an evaluation board for and click on Parts & Purchasing. Example:

 

Find the icons under Buy Now or Order Samples:

 
 

Click on the Buy Now icon and see who has stock and click on the Buy button:

 
 
 

Alternatively, you can click on the Order Samples

 
 

If the icons are missing, then contact Customer Support.

In PWM controllers, frequency is constant and tON (on-time) is set by the controller to regulate the output voltage. However in COT controllers, the tON is constant and set by the RON resistor. This also sets the frequency. RON is connected between the TON pin and GND.

If the high-side FET was ideal, the tON of the SW signal would be equal to tON of GH (high-side FET gate) signal and the relationship between RON and tON would be:

 
 

However, the high side FET has rise and fall times as well as on and off delay times, so the tON of SW is not equal to GH. This non-ideal characteristic is measured for each regulator or module where the above equation is modified. In the Applications Information of each regulator or module datasheet, an equation defining the relationship of RON and tON is given based on test data for that device. For example, in the XR79206 power module datasheet, you will find the following equation in the Programming the On-Time section of the Applications Information:

 
 
 

The correlation of this equation to the test data is also given in the datasheet. In the XR79206 example, Figure 5 in the Typical Performance Characteristics section shows very good correlation:

 
 
 In an ideal Buck Converter, tON is a function of VIN, VOUT and f expressed in following equation:
 
 

However, as no Buck Converter is ideal, test data is taken to determine a more accurate equation which is also given in the datasheet. In the XR79206 example, the following equation is given based on test data:

 
 
 

Substituting this tON equation into the above equation relating RON and tON and simplifying, we get:

 
 
 

Then RON can be easily chosen based on the targeted VIN, VOUT, frequency and efficiency. So for example in the XR79206, if VIN = 24V, VOUT = 5V, f = 500kHz and efficiency = 90%,

 
 
 
 
The next closest commercially available resistor value can be used. Several RON examples are given in the datasheets based on the above equation for your convenience. For a given RON it should be noted that tON is inversely proportional to VIN. This inverse relationship allows the frequency to remain constant as VIN changes, except for some changes due to the non-ideal nature of the power components. For example, this is illustrated in the following graph from the XR79206:
 
 
 

As IOUT increases, frequency increases slightly due to increasing power losses. As losses increase, more power must be delivered per cycle to keep VOUT constant. Because tON is constant, the period decreases and frequency increases, as can be seen in the following example from the XR79206 datasheet:

 
 
 
 
 
 
The best way to determine this is to go to exar.com and type the part into the search function. At or near the top of the results you should see something that looks like
 
 

In this example, we looked for XRA1201. When you hover over it, it will turn grey and you can click anywhere in the grey box. This brings you to the product page. For example:

 
 

Click on Parts & Purchasing, highlighted in yellow above. The screen changes to:

 

Notice the status column and the “Show obsolete parts” link:

 

A legend tells you the definition of the different statuses. Click on the “Show obsolete parts” link to see EOL or OBS part numbers along with the Active part numbers:

 
 

Another method to find out if a part is OBS or EOL is to click on SUPPORT:

 

And then Product Change Notifications

 
 

Type the part into the search, and click on one of the part numbers from the drop down menu. Then you can look for the Product Discontinuation Notice, which generally is at the top of the list, for example:

 
 

If you see this, it tells you that this particular orderable part has been discontinued and when the last order date is, or was. If you click on the file, then you can view the notice we sent about this if you purchased the part in the recent past. It may also advise of a replacement part. When an orderable part first becomes discontinued, Product Discontinuation Notices are sent are sent to those who have purchased the parts in the recent past, if purchased directly, with a dated opportunity to place a last order.

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