bd6757kn ROHM Co. Ltd., bd6757kn Datasheet - Page 9

• Manufacturer Part Number: bd6757kn
• Description: 7ch System Lens Drivers For Digital Still Cameras / Single-lens Reflex Cameras
• Manufacturer: ROHM Co. Ltd.

●Function Explanation
© 2009 ROHM Co., Ltd. All rights reserved.
BD6757KN, BD6889GU
www.rohm.com
1) Power-saving function
2) Motor Control input
3) H-bridge
4) Drive system of Linear Constant-Current H-bridge (BD6757KN: ch7 and BD6889GU: ch7)
5) Charge pump (BD6757KN)
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)
(1) INxA and INxB pins
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)
BD6757KN (ch7) and BD6889GU (ch7) enable Linear Constant-Current Driving.
(1) Reference voltage output (with a tolerance of ±2%)
(2) Output current settings and setting changes (BD6757KN)
(3) Output current detection and current settings
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).
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.
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)
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.
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)
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.
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.
If a 0.1μF capacitor is connected between: CP1 and CP2, CP3 and CP4, VG and GND
Then, VG pin output voltage will be:
If a 0.1μF capacitor is connected between: CP1 and CP2, VG and GND
Then, VG pin output voltage will be:
Output current value Iout[A] =
VLIMH[V] or VLIML[V]
VLIM[V]
RNF[Ω]
VM1 + (VCC  2)
CP4 and VG pins are shorted, and CP3 pin is open
VM1 + VCC
RNF[Ω]
(BD6889GU)
9/15
Select VLIMH when LIMSW is Low-level
Select VLIML when LIMSW is High-level
Technical Note
2009.06 - Rev.A
(BD6757KN)
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