Data Sheet

LTM8060F

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Rev. 0

24 of 43

including Y5V, and Z5U have very large temperature and voltage coefficients of capacitance. In an application

circuit, they may have only a small fraction of their nominal capacitance, resulting in a much higher output voltage

ripple than expected. The ceramic capacitors are also piezoelectric. In Burst Mode operation, the LTM8060F’s

switching frequency depends on the load current, and can excite a ceramic capacitor at audio frequencies,

generating audible noise. Since the LTM8060F operates at a lower current limit during Burst Mode operation, the

noise is typically very quiet to a casual ear. If this audible noise is unacceptable, use a high-performance

electrolytic capacitor at the output. It may also be a paralleled combination of a ceramic capacitor and a low-cost

electrolytic capacitor.

A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LTM8060F. A

ceramic input capacitor combined with trace or cable inductance forms a high-Q (underdamped) tank circuit. If the

LTM8060F circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly

exceeding the device’s rating. This situation can be avoided easily; see the Hot-Plugging Safely section.

Table 6. Recommended Component Values and Configuration (TA = 25°C)

VIN 1

(V)

VOUT

(V)

RFB

(Ω)

CIN 2

(μF)

COUT

(μF)

BIAS

CFF

(pF)

fSW

(Hz)

RT

(kΩ)

MAX fSW

(Hz)

MIN RT

(kΩ)

3 to 40

0.8

Open

4.7 50V X5R 1206

2 × 100 4V X5R 0805

3.2 to 10

100

400k

100

600k

64.9

3 to 40

1

1M

4.7 50V X5R 1206

2 × 100 4V X5R 0805

3.2 to 10

100

400k

100

725k

52.3

3 to 40

1.2

499k

4.7 50V X5R 1206

2 × 100 4V X5R 0805

3.2 to 10

68

500k

76.8

875k

42.2

3.2 to 40

1.5

287k

4.7 50V X5R 1206

2 × 100 4V X5R 0805

3.2 to 10

–

600k

64.9

1M

35.7

3.5 to 40

1.8

200k

4.7 50V X5R 1206

1 × 100 4V X5R 0805

3.2 to 10

–

650k

59

1.3M

25.5

3.5 to 40

2

165k

4.7 50V X5R 1206

1 × 100 4V X5R 0805

3.2 to 10

–

700k

54.9

1.4M

23.2

4.2 to 40

2.5

118k

4.7 50V X5R 1206

1 × 47 4V X5R 0805

3.2 to 10

–

800k

46.4

1.7M

18.2

5.5 to 40

3.3

78.7k

4.7 50V X5R 1206

1 × 47 6.3V X5R 0805

3.2 to 10

–

1M

35.7

2.2M

12.7

8.5 to 40

5

47.5k

4.7 50V X5R 1206

1 × 47 6.3V X5R 1206

3.2 to 10

–

1.2M

27.4

3M

8.06

11 to 40

8

27.4k

4.7 50V X5R 1206

1 × 47 10V X5R 1206

3.2 to 10

–

1.6M

19.6

3M

8.06

1

The LTM8060F may be capable of the operating at lower input voltages but may skip switching cycles.

2

A bulk input capacitor is required.

Frequency Selection

The LTM8060F uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to

3MHz by using a resistor connected from the RT pin to ground. Table 7 provides a list of RT resistor values and their

resultant frequencies. The resistors in Table 7 are standard 1% E96 values.

Operating Frequency Trade-Offs

It is recommended that the user apply the optimal RT value given in Table 7 for the input and output operating

conditions. When using the LTM8060F with different output voltages, the higher frequency recommended by Table

7 will usually result in the best operation. System level or other considerations, however, may necessitate another

operating frequency. While the LTM8060F is flexible enough to accommodate a wide range of operating

frequencies, a haphazardly chosen one may result in undesirable operation under certain operating or fault

conditions. A frequency that is too high can reduce efficiency, generate excessive heat, or even damage the

LTM8060F if the output is overloaded or short-circuited. A frequency that is too low can result in a final design that

has too much output ripple or too large of an output capacitor.

Table 7. Switching Frequency vs. RT Value