BD6757KN 查看數據表（PDF） - ROHM Semiconductor

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BD6757KN

7ch System Lens Drivers for Digital Still Cameras / Single-lens Reflex Cameras

ROHM Semiconductor 

BD6757KN, BD6889GU

Technical Note

●Function Explanation

1) Power-saving function

When Low-level voltage is applied to PS pin, the IC will be turned off internally and the circuit current will be 0μA (Typ.).

During operating mode, PS pin should be High-level. (See the Electrical Characteristics; p.2/16 and p.3/16)

2) Motor Control input

(1) INxA and INxB pins

These pins are used to program and control the motor drive modes. The Full-ON drivers and the Linear Constant-Current

driver use IN/IN and EN/IN input modes, respectively. (See the Electrical Characteristics; p.2/16 and p.3/16, and I/O Truth

Table; p.10/16)

3) H-bridge

The 7-channel H-bridges can be controlled independently. For this reason, it is possible to drive the H-bridges

simultaneously, as long as the package thermal tolerances are not exceeded.

The H-bridge output transistors of the BD6757KN and BD6889GU consist of Power DMOS, with the charge pump step-up

power supply VG, and Power CMOS, with the motor power supply VM, respectively. The total H-bridge ON-Resistance on

the high and low sides varies with the VG and VM voltages, respectively. The system must be designed so that the

maximum H-bridge current for each channel is 800mA or below. (See the Operating Conditions; p.1/16)

4) Drive system of Linear Constant-Current H-bridge (BD6757KN: ch7 and BD6889GU: ch7)

BD6757KN (ch7) and BD6889GU (ch7) enable Linear Constant-Current Driving.

(1) Reference voltage output (with a tolerance of ±2%)

The VREF pin outputs 0.9V, based on the internal reference voltage. The output current of the Constant-Current Drive

block is controllable by connecting external resistance to the VREF pin of the IC and applying a voltage divided by the

resistor to the output current setting pins. (BD6757KN: VLIMH and VLIML pins, BD6889GU: VLIM pin) It is

recommended to set the external resistance to 1kΩ or above in consideration of the current capacity of the VREF pin,

and 20kΩ or below in order to minimize the fluctuation of the set value caused by the base current of the internal

transistor of the IC.

(2) Output current settings and setting changes (BD6757KN)

When the Low-level control voltage is applied to the LIMSW pin, the value on the VLIMH pin will be used as an output

current set value to control the output current. When the High-level control voltage is applied to the LIMSW pin, the

value on the VLIML pin will be used as an output current set value to control the output current. (See the Electrical

Characteristics; P.2/16)

(3) Output current detection and current settings

By connecting external resistor (0.1Ω to 5.0Ω) to the RNF pin 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 RNF and SENSE pins and

comparing the voltage with the VLIMH or VLIML voltage (VLIM voltage in the case of the BD6889GU). To perform

output current settings more precisely, trim the external RNF resistance if needed, and supply a precise voltage externally to

the VLIMH or VLIML pin of the IC (VLIM pin in the case of the BD6889GU). In that case, open the VREF pin.

Output current value Iout[A] =

VLIMH[V] or VLIML[V]

RNF[Ω]

VLIM[V]

RNF[Ω]

(BD6889GU)

Select VLIMH when LIMSW is Low-level

Select VLIML when LIMSW is High-level

(BD6757KN)

･･････(1)

The output current is 400mA3% if 0.2V is applied to the VLIMH or VLIML pin (VLIM pin in the case of the

BD6889GU) and a 0.5Ω resistor is connected externally to the RNF pin.

If the VLIMH and VLIML pins (VLIM pin in the case of the BD6889GU) are shorted to the VCC pin (or the same voltage

level as the VCC is applied) and the SENSE and RNF pins are shorted to the ground, this channel can be used as a

Full-ON Drive H-bridge like the other six channels.

5) Charge pump (BD6757KN)

Each output H-bridge of the BD6757KN on the high and low sides consists of Nch DMOS. Therefore, the gate voltage VG

should be higher than the VM voltage to drive the Nch DMOS on the high side.

The BD6757KN has a built-in charge pump circuit that generates VG voltage by connecting an external capacitor (0.01μF

to 0.1μF).

If a 0.1μF capacitor is connected between: CP1 and CP2, CP3 and CP4, VG and GND

Then, VG pin output voltage will be:

VM1 + (VCC  2)

If a 0.1μF capacitor is connected between: CP1 and CP2, VG and GND

CP4 and VG pins are shorted, and CP3 pin is open

Then, VG pin output voltage will be:

VM1 + VCC

The VM1 to VM4 respectively can be set to voltages different to one another. In order to ensure better performance, the

voltage differential between VG and VM must be 4.5V or higher, and the VG voltage must not exceed the absolute

maximum rating of 15V.

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9/15

2009.06 - Rev.A

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