TPS54160: Question about equation in design example of worksheet Page 37 Equation 47.

Thank You Yang,

I would like to go to another equation in the app note:

Equation 51 and 48 calculate a R_C value.  When I plug in the values into the equation the numbers for Equation 51 seem to be wrong here is the 

C code I am using:

// 51

double R_C;
double gm_EA;
double VREF;
fz_MOD = 338.0e3;
gm_EA = 97.0e-6;
VREF = 0.8;
G_MOD_fc = 0.542;
cout << "fz_MOD = " << fz_MOD << endl;
cout << "gm_EA = " << gm_EA << endl;
cout << "VREF = " << VREF << endl;
cout << "VOUT = " << VOUT << endl;
cout << "G_MOD_fc = " << G_MOD_fc << endl;
//R_C = ( VOUT ) / ( G_MOD_fc * fc * gm_EA * VREF ); // 51 fz_MOD
//cout << ( G_MOD_fc * fz_MOD * gm_EA * VREF ) << endl;
R_C = VOUT / ( G_MOD_fc * fz_MOD * gm_EA * VREF ); // 51 fz_MOD
cout << "R_C = " << R_C << endl;
R_C = ( VOUT ) / ( G_MOD_fc * gm_EA * VREF ); // 48
cout << "R_C = " << R_C << endl;

And the output or values I used in the equations:

fz_MOD = 338000
gm_EA = 9.7e-05
VREF = 0.8
VOUT = 3.3
G_MOD_fc = 0.542
R_C = 0.232133
R_C = 78460.8

expected value is 

• RC = 76.2 kΩ

Not that for equation 51 it is very small:

Equation 48 seems reasonable.  The app note suggests need to use equation 51 for this example:

Expected values:

For the example problem, the ESR zero is located at a higher frequency compared to the crossover frequency so
Equation 50 through Equation 53 are used to calculate the compensation components. In this example, the
calculated components values are:
• RC = 76.2 kΩ
• CC = 2710 pF
• Cƒ = 6.17 pF

This is on page 38 of TPS54160.pdf data sheet.

Thanks.

App note SLVS9492.pdf   (heading at the top   TPS54620.  Entitled

TPS54620 4.5 to 17V input 6-A Synchronout Ste Downt Swift Converter

Calculating the Type 2 compensation resistor R4 in this app note

had an equation on page  28    equation number 35

R4_num = 2.0 * pi * fc * VOUT * COUT;
R4_denom = ( gm_ps * gm_EA * VREF );

R4 = R4_num / R4_denom;

I can get a resistance in the ball park especially if I change the fc = 36500

leaving all the other parameters the same.

double R4_num;
double R4_denom;
//double R4;

//fc = 0.1 * f_sw_hz;
fc = 36500.0;

R4_num = 2.0 * pi * fc * VOUT * COUT;
R4_denom = ( gm_ps * gm_EA * VREF );

R4 = R4_num / R4_denom;

cout << endl << endl << endl;

cout << "fc = " << fc << endl;
cout << "VOUT = " << VOUT << endl;
cout << "COUT = " << COUT << endl;
cout << "gm_ps = " << gm_ps << endl;
cout << "gm_EA = " << gm_EA << endl;
cout << "VREF = " << VREF << endl;
cout << endl;

cout << "R4_num = " << R4_num << endl;
cout << "R4_denom = " << R4_denom << endl;
cout << "R4 = " << R4 << endl;

Results of C++ output

fc = 36500
VOUT = 3.3
COUT = 4.7e-05
gm_ps = 6
gm_EA = 9.7e-05
VREF = 0.8

R4_num = 35.5701
R4_denom = 0.0004656
R4 = 76396.2

when fc is left at 45000

R4_num = 43.8535
R4_denom = 0.0004656
R4 = 94187.1

I agree with this as the answer to the first question.  I was hoping to hear more about the next question.