PTH12020LAH datasheet(11/27 Pages) TI

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Designing for Very Fast Load Transients

Adjusting the Output Voltage of the PTH12020x Series of Wide-Output Adjust Power Modules

Rset + 10 kW

0.8 V

Vout * Vmin

* Rs kW

(1)

PTH12020W/L

SLTS208E–MAY 2003–REVISED OCTOBER 2005

The transient response of the DC/DC converter has been characterized using a load transient with a di/dt of

1 A/µs. The typical voltage deviation for this load transient is given in the data sheet specification table using the

optional value of output capacitance. As the di/dt of a transient is increased, the response of a converter's

regulation circuit ultimately depends on its output capacitor decoupling network. This is an inherent limitation with

any DC/DC converter once the speed of the transient exceeds its bandwidth capability. If the target application

specifies a higher di/dt or lower voltage deviation, the requirement can only be met with additional output

capacitor decoupling. In these cases special attention must be paid to the type, value and ESR of the capacitors

selected.

If the transient performance requirements exceed that specified in the data sheet, or the total amount of load

capacitance is above 3000 µF, the selection of output capacitors becomes more important.

The VoAdjust control (pin 4) sets the output voltage of the PTH12020 product. The adjustment range is from

1.2 V to 5.5 V for the W-suffix modules, and 0.8 V to 1.8 V for L-suffix modules. The adjustment method requires

the addition of a single external resistor, Rset, that must be connected directly between the VoAdjust and GND

pins 1. Table 2 gives the preferred value of the external resistor for a number of standard voltages, along with

the actual output voltage that this resistance value provides. Figure 11 shows the placement of the required

resistor.

Table 2. Preferred Values of Rset for Standard Output Voltages

PTH12020W

PTH12020L

Vout

Rset

(Req'd)

(Actual)

5 V

280 Ω

5.009 V

N/A

3.3 V

2.0 kΩ

3.294 V

N/A

2.5 V

4.32 kΩ

2.503 V

N/A

2 V

8.06 kΩ

2.010 V

N/A

1.8 V

11.5 kΩ

1.801 V

130 Ω

1.800 V

1.5 V

24.3 kΩ

1.506 V

3.57 kΩ

1.499 V

1.2 V

Open

1.200 V

12.1 kΩ

1.201 V

1.1 V

N/A

18.7 kΩ

1.101 V

1.0 V

N/A

32.4 kΩ

0.999 V

0.9 V

N/A

71.5 kΩ

0.901 V

0.8 V

N/A

Open

0.800 V

For other output voltages the value of the required resistor can either be calculated, or simply selected from the

range of values given in Table 4. The equation below may be used for calculating the adjust resistor value.

Select the appropriate value for the parameters, Rs and Vmin, from Table 3.

Table 3. Adjust Formula Parameters

Pt. No.

PTH12020W

PTH12020L

Vmin

1.2 V

0.8 V

Vmax

5.5 V

1.8 V

1.82 kΩ

7.87 kΩ

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