Datasheet LTM8040 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | 36V, 1A μModule (Power Module) LED Driver and Current Source |
| Pages / Page | 20 / 10 — APPLICATION INFORMATION. BIAS Pin Considerations. Table 1. RT vs … |
| File Format / Size | PDF / 220 Kb |
| Document Language | English |
APPLICATION INFORMATION. BIAS Pin Considerations. Table 1. RT vs Frequency. T (kΩ). FREQUENCY (MHz)
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Text Version of Document
LTM8040
APPLICATION INFORMATION
If another frequency is desired, Table 1 shows suggested
BIAS Pin Considerations
RT selections for a variety of switching frequencies. For proper operation, the BIAS pin must be powered by
Table 1. RT vs Frequency
at least 2.6V. Figure 2 shows three ways to arrange the
R
circuit. For outputs of 2.6V or higher, the standard circuit
T (kΩ) FREQUENCY (MHz)
13 2.00 (Figure 2a) is recommended. For output voltages below 16 1.84 2.6V, the BIAS pin can be tied to the input (Figure 2b) at the cost of some effi ciency. Finally, the BIAS pin can be 18.7 1.70 tied to another source that is at least 2.6V (Figure 2c). 24.9 1.50 For example, if a 3.3V source is on whenever the LED is 29.4 1.37 on, the BIAS pin can be connected to the 3.3V output. In 35.7 1.25 all cases, be sure that the maximum voltage at the BIAS 54.9 1.00 pin is both less than 25V and the sum of VIN and BIAS is 75 0.90 less than 51V. If BIAS is powered by a source other than 88.7 0.85 LPWR, a local decoupling capacitor may be necessary. 137 0.75 The value of the decoupling capacitor is dependent upon 174 0.68 the source and PCB layout. 215 0.65 487 0.57 OPEN 0.50 LTM8040 LTM8040 VIN V V LEDA 3.3V IN IN V LEDA 2.5V 4V TO 36V IN 5.5V C1 SHDN LPWR C1 SHDN LPWR 2.2μF ADJ BIAS WHITE 2.2μF ADJ BIAS RED LED PWM LED PWM RT RT GND GND 8040 F02a 8040 F02b
Figure 2a. Tie BIAS to LPWR if LPWR is Greater Than 2.6V Figure 2b. BIAS May be Tied to VIN if LPWR is Below 2.6V
LTM8040 VIN V LEDA 2.5V IN 4V TO 36V C1 SHDN LPWR 2.2μF ADJ BIAS 3.3V PWM 1μF RED RT GND LED 8040 F02c
Figure 2c. Tie BIAS to an External Power Source if Neither VIN Nor LPWR are Suitable
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APPLICATION INFORMATION
If another frequency is desired, Table 1 shows suggested
BIAS Pin Considerations
RT selections for a variety of switching frequencies. For proper operation, the BIAS pin must be powered by
Table 1. RT vs Frequency
at least 2.6V. Figure 2 shows three ways to arrange the
R
circuit. For outputs of 2.6V or higher, the standard circuit
T (kΩ) FREQUENCY (MHz)
13 2.00 (Figure 2a) is recommended. For output voltages below 16 1.84 2.6V, the BIAS pin can be tied to the input (Figure 2b) at the cost of some effi ciency. Finally, the BIAS pin can be 18.7 1.70 tied to another source that is at least 2.6V (Figure 2c). 24.9 1.50 For example, if a 3.3V source is on whenever the LED is 29.4 1.37 on, the BIAS pin can be connected to the 3.3V output. In 35.7 1.25 all cases, be sure that the maximum voltage at the BIAS 54.9 1.00 pin is both less than 25V and the sum of VIN and BIAS is 75 0.90 less than 51V. If BIAS is powered by a source other than 88.7 0.85 LPWR, a local decoupling capacitor may be necessary. 137 0.75 The value of the decoupling capacitor is dependent upon 174 0.68 the source and PCB layout. 215 0.65 487 0.57 OPEN 0.50 LTM8040 LTM8040 VIN V V LEDA 3.3V IN IN V LEDA 2.5V 4V TO 36V IN 5.5V C1 SHDN LPWR C1 SHDN LPWR 2.2μF ADJ BIAS WHITE 2.2μF ADJ BIAS RED LED PWM LED PWM RT RT GND GND 8040 F02a 8040 F02b
Figure 2a. Tie BIAS to LPWR if LPWR is Greater Than 2.6V Figure 2b. BIAS May be Tied to VIN if LPWR is Below 2.6V
LTM8040 VIN V LEDA 2.5V IN 4V TO 36V C1 SHDN LPWR 2.2μF ADJ BIAS 3.3V PWM 1μF RED RT GND LED 8040 F02c
Figure 2c. Tie BIAS to an External Power Source if Neither VIN Nor LPWR are Suitable
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