LB1847

No.5982-13/15

4. Simultaneous ON prevention function

This IC incorporates a circuit to prevent feed-through current when phase switching. For reference, the output ON and

OFF delay times at PHASE and ENABLE switching are given below.

Reference Data * typical value

Sink side

Source side

ON delay time

1.9

µs

2.2

µs

PHASE switching

(Low

→ Hi)

OFF deley time

0.8

µs

1.8

µs

ON delay time

1.4

µs

1.7

µs

PHASE switching

(Hi

→ Low)

OFF deley time

0.9

µs

1.35

µs

ON delay time

2.15

µs

2.75

µs

ENABLE switching

OFF deley time

1.2

µs

5.8

µs

5. Noise canceler

This IC has a noise canceling function to prevent malfunction due to noise spikes generated when switching ON. The

noise cancel time tn is determined by internal resistance of the CR pin and the constant of the externally connected CR

components. The constant also determines the switching OFF time.

Figure 1 shows the internal configuration at the CR pin, and Figure 2 the CR pin constant setting range.

Equation when logic voltage VCC = 5V

CR pin voltage E1 = VCC × R / (R1 + R2 + R) [V]

Noise cancel time tn

≈ (R1 + R2)× C × 1n {(E1 − 1.5) / (E1 − 4.0)} [s]

Switching OFF time toff

≈ –R × C × 1n (1.5 / E1) [s]

Internal resistance at CR pin : R1 = 1k

Ω, R2 = 300Ω (typ.)

*The CR constant setting range in Figure 2 on page 15 is given for reference. It applies to a switching OFF time in the

range from 8 to 100

µs. The switching time can also be made higher than 100 ms. However, a capacitor value of more

than several thousand pF will result in longer noise canceling time, which can cause the output current to become

higher than the set current. The longer switching OFF time results in higher output current ripple, causing a drop in

average current and rotation efficiency. When keeping the switching OFF time within 100 ms, it is recommended to

stay within the CR constant range shown in Figure 2.

Internal configuration at CR pin

C:470pF

R2

One-shot multi-blanking

time circuit

CR pin

E1

1k

Ω

R1

300

Ω

R:15k

Ω

VCC line

Figure 1