LM2694SD datasheet(16/19 Pages) NSC

16 / 19 page

Applications Information (Continued)

Item

Description

Value

Ceramic Capacitor

3.3 µF, 50V

Ceramic Capacitor

22 µF, 16V

C4, C6

Ceramic Capacitor

0.022 µF, 16V

C3, C5

Ceramic Capacitor

0.1 µF, 50V

Schottky Diode

60V, 1A

Inductor

150 µH

Resistor

2.5 k

Ω

Resistor

2.5 k

Ω

Resistor

1.5

Ω

Resistor

140 k

Ω

National Semi LM2694

MINIMUM LOAD CURRENT

The LM2694 requires a minimum load current of 500 µA. If

the load current falls below that level, the bootstrap capacitor

(C4) may discharge during the long off-time, and the circuit

will either shutdown, or cycle on and off at a low frequency.

If the load current is expected to drop below 500 µA in the

application, R1 and R2 should be chosen low enough in

value so they provide the minimum required current at nomi-

nal V

OUT.

LOW OUTPUT RIPPLE CONFIGURATIONS

For applications where low output voltage ripple is required

the output can be taken directly from the low ESR output

capacitor (C2) as shown in Figure 16. However, R3 slightly

degrades the load regulation. The specific component val-

ues, and the application determine if this is suitable.

Where the circuit of Figure 16 is not suitable for reducing

output ripple, the circuits of Figure 17 or Figure 18 can be

used.

20187032

FIGURE 14. Efficiency vs Load Current and V

Circuit of Figure 13

20187033

FIGURE 15. Frequency vs V

Circuit of Figure 13

20187034

FIGURE 16. Low Ripple Output

20187035

FIGURE 17. Low Output Ripple Using a Feedforward

Capacitor

LM2694SD Datasheet(PDF) 16 Page - National Semiconductor (TI)

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