BD6757KN Ver la hoja de datos (PDF) - ROHM Semiconductor

Número de pieza

componentes Descripción

Fabricante

BD6757KN

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

ROHM Semiconductor 

BD6757KN, BD6889GU

Technical Note

●Heat Dissipation

1) Power Consumption

The power consumption of the IC (Pw) is expressed by the following formula.

Pw[W] = VCC[V]  ICC[A] + Iout2[A2]  RON[Ω] (Full-ON Drive block and PWM Constant-Current Drive block)

= VCC[V]  ICC[A] + Iout[A]  (VM[V] - VRNF[V] - Iout[A]  Rm[Ω]) (Linear Constant-Current Drive block)

Pw: Power consumption of the IC

VCC: Power supply voltage on the VCC pin

ICC: Current consumption of the VCC pin

Iout: Current consumption of the VM pin on the drive channel

RON: Total ON-Resistance on the high and low drive channel

VM: Power supply voltage on the VM pin on the drive channel

VRNF: Voltage on the RNF pin on the drive channel

Rm: Resistance on the motor on the drive channel

･･････(2)

･･････(3)

While in operation, check that the junction temperature (Tjmax) of the IC will not be in excess of 150℃, in consideration

of formula (2), formula (3), the package power (Pd), and ambient temperature (Ta). If the junction temperature exceeds

150℃, the IC will not work as a properly. This can cause problems, such as parasitic oscillation and temperature leakage.

If the IC is used under such conditions, it will result in characteristic degradation and eventually fail. Be sure to keep the

junction temperature lower than 150℃.

2) Measurement Method of Junction Temperature

The junction temperature can be measured by the following method.

By using the diode temperature characteristics of the control input pin, on a

VIN

channel that is not driven, the junction temperature X can be measured in a

pseudo manner.

GND

V

50μA

Fig.20 Tjmax Measurement Circuit Diagram

The junction temperature X[℃] under certain conditions is expressed by formula

(4), provided that the temperature characteristic of the diode is -2 mV/℃

X[°C] =

a - b[mV]

-2 [mV/°C]

+ 25[°C]

X: Junction temperature

a: The voltmeter V value at a junction temperature of 25℃

b: The voltmeter V value at a junction temperature of X℃

-2: Temperature characteristic of diode

･･････(4)

If the exact junction temperature is desired, it is necessary to measure the specific temperature characteristic of the

internal diode, of each IC.

●Notes for use

1) Absolute maximum ratings

Use of the IC in excess of absolute maximum ratings such as the applied voltage or operating temperature range may

result in IC damage. Assumptions should not be made regarding the state of the IC (short mode or open mode) when

such damage is suffered. The implementation of a physical safety measure such as a fuse should be considered when

use of the IC in a special mode where the absolute maximum ratings may be exceeded is anticipated.

2) Storage temperature range

As long as the IC is kept within this range, there should be no problems in the IC’s performance. Conversely, extreme

temperature changes may result in poor IC performance, even if the changes are within the above range.

3) Power supply pins and lines

None of the VM line for the H-bridges is internally connected to the VCC power supply line, which is only for the control

logic or analog circuit. Therefore, the VM and VCC lines can be driven at different voltages. Although these lines can be

connected to a common power supply, do not open the power supply pin but connect it to the power supply externally.

Regenerated current may flow as a result of the motor's back electromotive force. Insert capacitors between the power

supply and ground pins to serve as a route for regenerated current. Determine the capacitance in full consideration of all

the characteristics of the electrolytic capacitor, because the electrolytic capacitor may loose some capacitance at low

temperatures. If the connected power supply does not have sufficient current absorption capacity, regenerative current

will cause the voltage on the power supply line to rise, which combined with the product and its peripheral circuitry may

exceed the absolute maximum ratings. It is recommended to implement a physical safety measure such as the insertion

of a voltage clamp diode between the power supply and ground pins.

For this IC with several power supplies and a part consists of the CMOS block, it is possible that rush current may flow

instantaneously due to the internal powering sequence and delays, and to the unstable internal logic, respectively. Therefore,

give special consideration to power coupling capacitance, width of power and ground wirings, and routing of wiring.

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

13/15

2009.06 - Rev.A

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