R16DS0137EU0100 Rev.1.0

Page 18

Apr 13, 2021

RAA210040 Datasheet

5.12 Thermal Shutdown

The RAA210040 has built-in thermal protection. When the internal temperature reaches +150°C, the module shuts

down. Both MOSFETs are turned off and PG goes low. As the temperature drops to +125°C, the RAA210040 resumes

operation by stepping through the soft start-up.

6.

Application Information

6.1

Output Voltage Programming

The output voltage of the module is programmed by an external resistor divider (R1 and R2 in Figure 3). R2

combined with the internal 100kΩ 0.5% resistor connected from FB to VSENSE forms a resistor divider that sets

the output voltage. The output voltage is governed by Equation 2.

Note: The output voltage accuracy is also dependent on the resistor accuracy of R1 and R2. You need to select

high accuracy resistors to achieve the overall output accuracy.

6.2

Switching Frequency Selection

With varieties of input and output voltage combinations, you must choose wisely on which frequency to operate at

according to the specific applications. The selection of switching frequency for each VIN and VOUT combination

needs to take into account a few trade-offs. Generally, lower switching frequency leads to higher efficiency at the

cost of higher output voltage ripple. Do not decrease the switching frequency too low because of the negative

current protection limit. Do not increase the switching frequency too high because of the minimum on-time limit,

especially at low VOUT. Moreover, when the output voltage is relatively high, low switching frequency results in

more sub-harmonic oscillation. Therefore, operating frequency needs to be kept relatively high under high VOUT

conditions. However, to ensure better thermal performance, the switching frequency cannot be increased too

much.

6.3

Input Capacitor Selection

The selection of the input filter capacitor is based on how much ripple the supply can tolerate on the DC input line.

The larger the capacitor, the less ripple expected; however, you need to consider the higher surge current during

power-up. The RAA210040 provides a soft start-up function that controls and limits the current surge. The total

capacitance of the input capacitor is calculated using Equation 3:

(EQ. 2)

Table 3. Output Voltage Resistor Settings

VOUT (V)

R1 (kΩ)R2 (kΩ)

0.6

100

open

0.8

100

301

0.9

100

200

1.0

100

150

1.2

100

100

1.5

100

66.5

1.8

100

49.9

2.5

100

31.6

3.3

100

22.1

VOUT

VREF

R2 R1

+

R2

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