JAJSM60B January 2023 – January 2024 LMR38020-Q1
PRODUCTION DATA
The switching frequency of the LMR38020-Q1 can be programmed by the resistor RT from the RT/SYNC pin and GND pin. The RT/SYNC pin cannot be left floating or shorted to ground. To determine the timing resistance for a given switching frequency, use Equation 2 or the curve in Figure 7-4. Table 7-1 gives typical RT values for a given fSW.
fSW (kHz) | RT (kΩ) |
---|---|
200 | 133 |
400 | 64.9 |
500 | 52.3 |
750 | 34.8 |
1000 | 25.5 |
1500 | 16.9 |
2000 | 12.7 |
2200 | 11.5 |
The LMR38020-Q1 switching action can also be synchronized to an external clock from 300 kHz to 2.1 MHz. Connect a square wave to the RT/SYNC pin through either circuit network shown in Figure 7-5. The internal oscillator is synchronized by the falling edge of external clock. The recommendations for the external clock include: high level no lower than 2.0 V, low level no higher than 0.6 V, and have a pulse width greater than 50 ns. When using a low impedance signal source, the frequency setting resistor RT is connected in parallel with an AC coupling capacitor, CCOUP, to a termination resistor, RTERM (for example, 50 Ω). The two resistors in series provide the default frequency setting resistance when the signal source is turned off. A 10-pF ceramic capacitor can be used for CCOUP.