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BD63520AEFV

TSZ02201-0P2P0B701530-1-2

© 2016 ROHM Co., Ltd. All rights reserved.

17.Aug.2016 Rev.001

www.rohm.com

TSZ22111・15・001

○PWM Constant current control

1) Current control operation

When the output transistor is turned on, the output current increases, raising the voltage over the current sense resistor.

When the voltage on the RNF pin reaches the voltage value set by the internal 2-bit DAC and the VREF input voltage, the

current limit comparator engages and enters current decay mode. The output is then held off for a period of time

determined by the RC time constant connected to the CR pin. The process repeats itself constantly for PWM operation.

2) Noise-masking function

In order to avoid misdetection of output current due to RNF spikes that may occur when the output turns ON, the IC

after the output transistor is turned on. This allows for constant-current drive without the need for an external filter. This

noise-masking period defines the minimum ON-time for the motor output transistor.

3) CR Timer

The CR filter connected to the CR pin is repeatedly charged and discharged between the VCRH and VCRL levels. The

output of the internal comparator is masked while charging from VCRL to VCRH in order to cancel noise. (As mentioned

above, this period defines the minimum ON-time of the motor output transistor.) The CR terminal begins discharging once

the voltage reaches VCRH. When the output current reaches the current limit during this period (i.e. RNF voltage reaches

the decay trigger voltage), then the IC enters decay mode. The CR continues to discharge during this period until it reaches

VCRL, at which point the IC output is switched back ON. The current output and CR pin begin charging simultaneously.

VCR=V･R/(R'+R)

V: internal regulator voltage 5V(Typ)

R': CR terminal internal impedance 5kΩ(Typ)

α:See the right graph.

Figure 4 Timing chart of CR voltage, RNF voltage and output current

Attach a resistor of at least 10 kΩ to the CR terminal (10 kΩ~200 kΩ recommended) as lower values may keep the RC from

reaching the VCRH voltage level. A capacitor in the range of 470 pF – 1500 pF is also recommended. As the capacitance

exceed the current limit threshold due to the internal L and R components of the output motor coil. Also, ensure that the

average output current and yielding lower output rotation efficiency. The optimal value should reduce the motor drive noise

while keeping distortion of the output current waveform to a minimum.

CR Voltage

RNF Voltage

Output current

Spike noise

Current limit Value

GND

Minimum ON Time

VCRH(1.0V typ)

VCRL(0.4V typ)

GND

0mA

Current limit Value

Chopping Period

Discharge time

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0

500

1000

1500

2000

C　[pF]