Datasheet

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Designing for Fast Load Transients
Adjusting the Output Voltage
R
SET
+ 10 kW
0.8 V
V
O
* 0.8 V
* 2.49 kW
(1)
PTV05010W
SLTS242A – FEBRUARY 2005 – 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
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 V
O
Adjust control (pin 4) sets the output voltage of the PTV05010W product to a value over the range, 0.8 V
to 3.6 V. The adjustment method requires the addition of a single external resistor, R
SET
, that must be connected
directly between the V
O
Adjust and the regulator's output GND (pin 1 is recommended). Without an adjust
resistor, the output voltage is set to its lowest value. 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 6
shows the placement of the required resistor.
Table 2. Nearest Standard Values of R
SET
for Common Output Voltages
V
O
R
SET
V
O
(Required) (Standard Value) (Actual)
3.3 V 698 Ω 3.309 V
2.5 V 2.21 k Ω 2.502 V
2 V 4.12 k Ω 2.010 V
1.8 V 5.49 k Ω 1.803 V
1.5 V 8.87 k Ω 1.504 V
1.2 V 17.4 k Ω 1.202 V
1 V 36.5 k Ω 1.005 V
0.8 V 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 3 . Equation 1 may be used for calculating the adjust resistor value.
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