REV. JUN 27, 2003
Page 8 of 12
HWD DC/DC Series Data Sheet
Output Voltage Adjustment
Output voltage adjustment is accomplished by connecting an external resistor between the Trim Pin and either the
+Vo1 or –Vo1 Pins.
With an external resistor between the Trim Pin and +Vo1 Pin (Radj-down) the output voltage set point (Vo,adj)
decreases. The following equation determines the required external resistor value to obtain an adjusted output
voltage:
Radj, dn= [ B -
,- ,
) - ,(
adjVonomVo
ADadjVo
] ohm
Where Radj-down is the resistance value and A, B, and D are defined in Table 7.
With an external resistor between the Trim Pin and –Vo1 Pin (Radj-up) the output voltage set point (Vo,adj)
increases. The following equation determines the required external resistor value to obtain an adjusted output
voltage:
Radj, up= [ B -
C - D) -,(
D •
adjVo
A
] ohm
Where Radj-up is the resistance value and A, B, C, and D are defined in Table 12.
Table 12.Output Adjustment Variables
Output A B C D
Vo1 4990 2000 2.5 2.5
Vo2 4990 2000 0.8 2.5
THERMAL CONSIDERATIONS
The power converter operates in a variety of thermal environments: however, sufficient cooling should be provided
to help ensure reliable operation of the converter. Heat-dissipating components are thermally coupled to the case.
Heat is removed by conduction, convection, and radiation to the surrounding environment. Proper cooling can be
verified by measuring the case temperature.
Heat Transfer Characteristics
Increasing airflow over the converter enhances the heat transfer via convection. Figure 4 shows the maximum
power that can be dissipated by the converter without exceeding the maximum case temperature versus local
ambient temperature (T
A
) for natural convection through 400 ft/min.
Systems in which these converters are used generate airflow rates of 50 ft/min due to other heat dissipating
components in the system. Therefore, the natural convection condition represents airflow rates of approximately
50 ft/min. Use of Figure 4 is shown in the following example.
Example
What is the minimum airflow required for the device operating at 24 V, an output power of 60 W, and maximum
ambient temperature of 60 ºC.
Solution:
Given: Vi = 24 V, Po = 60 W, T
A
= 60 ºC.
Determine P
D
(Figure 4): P
D
= 13 W.
Determine airflow (Figure 4): v = 200 ft/min
