LM5177: schematic review

Jeff YANG

Mastermind 7795 points

Part Number: LM5177

Tool/software:

Hi,

Would you please help us review attached schematic? thanks!

1307.lm5177.pdf

5 months ago

0 Stefan Schauer 5 months ago

TI__Guru 58601 points

HI Jeff,

Could you please attach the filled out LM51770 Quickstart-Calculator to this thread? This would be the most efficient workflow for us to do a schematic review.

Note: I recommend to use the newer version LM51770 (which is pin compatible)

Best regards,

Stefan

0 Jeff YANG 5 months ago in reply to Stefan Schauer

Mastermind 7795 points

Hi Stefan,

Please see the attached file, we have follow the excel caculator to modified some component and update the schematic.

Thanks!

LM51770 Buck-Boost Quickstart Tool V1_0_0.xlsm

LM5177DCPR_12VSB_1 (1).pdf

+1 Stefan Schauer 5 months ago in reply to Jeff YANG

TI__Guru 58601 points

HI Jeff,

I have seen that you have not changed to the LM51770 - is there a reason for that?

Please see below my review list and bold marked line items which should be checked again (Note: other info are left here to give an overview of what has been checked)

(Underlined parts not checked as info is missing)

Checked with Quickstart Calculator

Schematic:

Recommend to use LM51770 (newer and to replace LM5177)
Rcs in series with inductor and before inductor
Check filter for Rcs
Current sense Resistor Rcs does not have the required filter
Check filter for Risns
Current sense Resistor Risns does not have the filter - recommend to add place holder

Connect IMONOUT to VCC if ISNS not used
Snubber on SW1 and SW2
Place Footprint for a snubber at SW1 and SW2
(they can then be populated in case needed (e.g. due to EMI) without layout change)
Note: Snubber connect Resistor to GND for better Thermal performance

BIAS connected
If BIAS is not used connect to GND or VIN of VOUT (do not keep open)
BIAS can be connected to VIN (if the max ratings of BIAS are not violated) to benefit from the better performance of the LDO on BIAS

Add Series Resistor into MOSFET Gate signals lines
(they can then be replaced in case needed (e.g. due to EMI) without layout change,
additional option: add a diode in parallel for slow on and fast off.
Note: Good starting value is 3.3Ω and then adjust in when testing out the PCB
Voltage rating of MOSFET
(Have a margin of 30% is recommended)
Miller Plateau of MOSFETs
used MOSFETs need to be logic level MOSFETs - can be seen by Miller Plateau in the range of 2.5V-3.5V
UVLO setting relative to lowest input voltage
UVLO is set to xV but operating range starts at xV - relative large distance
Cap at VCC (EVM uses: 47uF) : (Datasheet min: 10uF with DC Bias
please check the cap on Vcc to have the required capacitance considering DC BIAS - we use a 47uF on the EVM