BD6373GW データシートの表示（PDF） - ROHM Semiconductor

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BD6373GW

6ch System Lens Drivers for Digital Still Cameras / Single-lens Reflex Cameras

ROHM Semiconductor 

BD6373GW, BD6873KN, BD6753KV

Technical Note

5) Drive system of PWM Constant-Current H-bridge (BD6753KV: ch5 and ch6)

BD6753KV (ch5 and ch6) enable peak current control PWM Constant-Current Driving.

(1) Output current detection and current settings

By connecting external resistance (0.1Ω to 5.0Ω) to the RNF3 and RNF4 pins of the IC, the motor drive current will be

converted into voltage in order to be detected. The output current is kept constant by shorting the RNF3 and RNF4 pins with

the SENSE3 and SENSE4 pins, respectively, and comparing the voltage to the set voltage input from outside the IC to the

VLIM5 and VLIM6 pins. As with the BD6873KN, the reference voltage generated inside the IC (VREF pin: 0.9V±10%) can

be divided using external resistors (from 1kΩ to 20kΩ). The resulting value can be input as the set voltage.

It is also necessary to connect a resistor and capacitor to the CR1 and CR2 pins, to determine the PWM drive off time.

(2) PWM Constant-Current control operation

When the output current in output ON mode increases, and the RNF3 or RNF4 voltage reaches the value set with the

VLIM5 or VLIM6 voltage, the internal current limiting comparator operates to set the IC to short mode. This caused the

current to be attenuated so that the H-bridge's low-side DMOS is ON. Once the off time (Toff) ends, as measured by

the CR timer, the IC returns to output ON mode. By repeating this cycle, the IC maintains a fixed current due to the

motor's inductance characteristics.

(3) Noise cancellation function

In order to avoid false detections by the current limiting comparator (caused by spike noise generated when output is

turned on), the IC uses the noise cancellation time (Tn) to disable current detection. This begins from the time output

turns on, until the noise cancellation time elapses. The noise cancellation time represents the minimum on time, and is

determined by the CR pin's internal resistor, external resistor, and capacitor.

(4) CR timer

When output turns on, the CR pin is clamped at approximately 0.9V. When the mode changes to short mode, it

discharges to approximately 0.4V. The interval over which this 0.5V voltage differential is discharged, is determined by

the off time (Toff). Once the CR pin voltage reaches 0.4V, the pin begins to charge as the output turns on, until it

reaches 0.9V. The interval over which the pin charges from 0.4V to approximately 0.8V is given by the noise

cancellation time (Tn). Toff and Tn are determined by the external resistor and capacitor connected to the CR pin.

A low resistance value to the CR pin will prevent it from reaching the clamp voltage. Therefore a resistor from 5 kΩ to

50kΩ should be used. Capacitors should be from 10pF to 2200pF. The use of a capacitance in excess of 2200pF will

lengthen the noise cancellation time and may cause the output current to exceed the set current. Setting a longer off

time may increase the output current ripple, reducing both the average current and the motor's rotational efficiency.

VLIM5[V]

VLIM6[V]

Output current value Iout[A] =

RNF3[Ω]

or

RNF4[Ω]

･･････(2)

Output current: Iout[A]

RNF voltage: VRNF[V]

Spike noise

CR voltage: VCR[V]

Noise cancellation time: Tn[sec]

Discharge period

Off time: Toff[sec]

PWM Constant-Current

setting value

0A

VLIM pin setting voltage

0V

0.9V

0.8V

0.4V

Charge period

Fig.21 BD6753KV Peak Current Control PWM Constant-Current Drive Using the CR Timer

If the VLIM5 or VLIM6 is shorted to the VCC pin (or the same voltage level as the VCC is applied) and the SENSE3 or

SENSE4 and RNF3 or RNF4 pins are shorted to the ground, this channel can be used as a Full-ON Drive H-bridge

like the other four channels.

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© 2009 ROHM Co., Ltd. All rights reserved.

11/17

2009.06 - Rev.A

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