Q: The MAX17599 circuit is designed based on MAXREFDES48#, and there’s a resistor R16 from pin VDRV to CS in the MAXREFDES48# schematic as shown below.The output of MAX17599 is interrupt during hot-swap at the load. It was measured over current project during the issue. How to modify the circuit & want to know how to choose this resistor? Is there a formula to calculate the value of this resistor?
A: The purpose of the resistor R16 is to apply a DC bias to the CS pin so that the voltage on the current resistor R18 is reduced for a certain desired peak current limit. This allows the power dissipation of the R18 resistor to be reduced and improve efficiency.
Please see the formulas to calculate for the resistors R16 and R18 below. The resistor, R17 and capacitor, C11 are always selected at 220Ω and 1000pF respectively. VR18max can be chosen value between 290mV and 150mV.
, where R17=220Ω, C11=1000pF, 290mV≥VR18max≥150mV
For example, you calculate the maximum primary peak current, Ipeak_max equal 5A and select VR18max=150mA. The R16 and R18 are calculated as table below:
A: The purpose of the resistor R16 is to apply a DC bias to the CS pin so that the voltage on the current resistor R18 is reduced for a certain desired peak current limit. This allows the power dissipation of the R18 resistor to be reduced and improve efficiency.
Please see the formulas to calculate for the resistors R16 and R18 below. The resistor, R17 and capacitor, C11 are always selected at 220Ω and 1000pF respectively. VR18max can be chosen value between 290mV and 150mV.
For example, you calculate the maximum primary peak current, Ipeak_max equal 5A and select VR18max=150mA. The R16 and R18 are calculated as table below:
|
R16(Ω)
|
R18(Ω)
|
VR18max(V)
|
Vcs-peak(V)
|
VDRV(V)
|
R17(Ω)
|
C119pF)
|
Ipeakmax(A)
|
|
7401.4
|
0.03
|
0.15
|
0.29
|
5
|
220
|
1000
|
5
|