LMP92066: Voltage regulator to source -5v

Hi Vaishak,

Erin will review and provide a response when they are back in office tomorrow. 

Best,

Katlynne Jones

Hi paul,
So basically negative voltage has to be fed to TPS7A3301RGWR right ?

Hi Vaishak,

Yes, you would need a generic negative supply to power the TPS7A3301 to receive a precise negative supply for the LMP92066.

For example, to get an output of -5.5V, you would want a voltage input of around -7V to -11V. I've added the LDO team to further assist you with picking a suitable voltage supply.

Thanks,
Erin

Thank you Erin for your feedback. I would like to hear the inputs from LDO team as well !

Regards,
Vaishak. B

Hi Vaishak,

LM27761 (charge pump + integrated LDO) can be used to convert +5.5V input to -5V output. Would this work for you?

Best regards,

Varun

Hi Varun,
In my RFE design,I am using 4 Bias controller (LMP92066) to bias the 4 Hybrid PAs (LDMOS+GaN). Kindly Suggest me a compatible power source to power the 4 quantities of LMP92066. I have an input voltage of 6V.

Regards, 
Vaishak B

Hi Vaishak,

The LM27761 can only run from max +5.5V input. I think there are 2 options for you.

1. Use an LDO to convert from +6V to +5.5V and then use the LM27761 to convert to -5V. 

2. Use an inverting buck boost to convert +6V to -7V. Use a high PSRR LDO like TPS7A3301 to convert -7V to -5V.

Since the LMP92066 may require a low noise supply, it would be beneficial to use an LDO that has a high PSRR. The TPS7A3301 has higher PSRR than the integrated LDO in LM27761.

Let me know which approach you prefer. 

Best regards,

Varun

Hi Varun,
Suppose i am using LM27761 (charge pump + integrated LDO). How many number of LM27761 is required to source the negative voltage for 4 number of LMP92066 ? 

Regards,
Vaishak B

Hi Vaishak,

From a load current point of view, the LM27761 can support 250mA output current. So it really depends on how much current is required by each LMP92066 part.

Erin Guthrie does each LMP92066 require 200mA for the negative supply?

Best regards,

Varun

Hi Varun,

200mA would be adequate for all 4 LMPs together. I think at minimum you would want 100mA total, but 200mA would give good headroom.

Thanks,
Erin

Hi Erin and Varun,
The datasheet of LMP92066 states that the VSSB requires 50mA minimum. (page 54 in datasheet). Can you please let me know regarding this ?

Regards,
Vaishak

Hi Erin and Varun,
Can you please help me out to resolve this.

Regards,
Vaishak

Hi Vaishak,

There is a US holiday today so there may be a delay in response until either tomorrow or Monday.

Best,

Katlynne Jones

Hi Vaishak,

The VSSB supply provides current for the DAC outputs. Each DAC output is max 10mA output, so with two DAC outputs and the base current of the pin, the VSSB supply needs to be at least 25mA. 50mA per device gives additional headroom, but is certainly not required. The LM27761 will be able to easily support all 4 LMPs.

Thanks,
Erin

Thank you Erin for clarifying the doubt. Also, I need some other inputs as well.
1.)My design has 4 final PA (Manf P/N-A5M36TG140)  which is GaN + LDMOS (One stage is LDMOS and Another stage is GaN). i am using 4 qty of LMP92066 as bias controller.to control all 4 PAs. How can i Interface the 4 PAs with 4 qty of bias controllers. Each PA needs GaN gate voltage and LDMOS gate voltage as well. 
2.) Initially I planned to use 2 LMP92066 to source 4 GaN stages of PA and 2 more LMP92066 to Source 4 qty LDMOS stages PAs. Is this approach fine ? 
Please let me know your thoughts. This is for the first time we are using this PA and Bias controller.

Regards,
Vaishak B

Hi Vaishak,

In theory, using 4 LMPs to control the 4 PAs will work fine. You may run into issues when it comes to the temperature compensation, though, as you will be controlling two separate PAs with the one controller. To measure the temperature accurately you will need to place the LMP as close to the PA as possible, so you will effectively be controlling two PAs with one PA's temperature. I believe this will be the only issue you will have, though.

Thanks,
Erin

Hi Erin,
I am not able to understand regarding temperature compensation. No where in the PA datasheet they have mentioned regarding temperature compensation and measurement.  Can you please help me out on this ? 

Hi Vaishak,

Read up on the Look Up Table information on page 15 of the datasheet. This device measures the ambient temperature and adjusts the DAC output to keep a constant gate bias for the PA. 

Thanks,
Erin

Hi Erin,
Thank you for your inputs.
So as per you, It is advisable to use 8 LMPs to control 4 PAs right ?

Regards,
Vaishak B 

Hi Vaishak,

For best performance, 8 LMPs would likely be best due to the temperature compensation. If that does not matter as much to you, 4 LMPs would work fine. 

We have a few other controllers you may be interested in as well: for example, the AFE20408. This device has 4 outputs with the ability of two to be in positive range, and 2 in negative range. This device is intended for dual stage PAs like the one you are using. 

A primary difference from the LMP is that this device does not have the closed loop temperature compensation. As such, you would need constant monitoring over I2C or SPI to adjust the output voltage with changes to temperature. 

The AFE20408 is expanded industrial rated, and we are on schedule to release a catalog version of the device later this year. 

Thanks,
Erin

HI Erin , 
I came across AMC7932 which supports both GaN and LDMOS bias voltages.

Hi Vaishak,

The AMC7932 is a good choice. Note that it does not have fast output switching, remote temperature sensing, or closed loop operation. If you do not require these aspects for your design, then the AMC7932 will consolidate the required DACs into one device. I'm the application engineer for the AMC7932 as well, so let me know if you have any questions about it.

Thanks,
Erin

Hi erin,
So there is no any other part which is specification wise equivalent to LMP92066 and with both GaN and LDMOS output ?

Hi Erin,
My biasing sequence will be in this manner- 

Bias ON the GaN stage first
1. Set gate voltage VGC2 and VGP2 to –5 V.
2. Set drain voltage VDC2 and VDP2 to nominal supply voltage (+48 V).
3. Increase VGP2 (peaking side) until IDQP2 = 35 mA current is attained, and then subtract 1.0 V for final VGP2 bias voltage.
4. Increase VGC2 (carrier side) until IDQC2 current is attained.

Bias ON the LDMOS driver stage second
5. Set drain voltage VDC1 and VDP1 to nominal supply voltage (+5 V).
6. Increase VGC1 (carrier side) until IDQC1 current is attained. 7. Increase VGP1 (peaking side) until IDQP1 current is attained.
8. Apply RF input power to desired level.

pls suggest a suitable bias controller. Total number of PA used will be 4 qty.