bd6757kn ROHM Co. Ltd., bd6757kn Datasheet - Page 13

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

●Heat Dissipation
●Notes for use
© 2009 ROHM Co., Ltd. All rights reserved.
BD6757KN, BD6889GU
www.rohm.com
1) Power Consumption
2) Measurement Method of Junction Temperature
1) Absolute maximum ratings
2) Storage temperature range
3) Power supply pins and lines
Fig.20 Tjmax Measurement Circuit Diagram
The power consumption of the IC (Pw) is expressed by the following formula.
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℃.
The junction temperature can be measured by the following method.
If the exact junction temperature is desired, it is necessary to measure the specific temperature characteristic of the
internal diode, of each IC.
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.
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.
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.
Pw[W] = VCC[V]  ICC[A] + Iout
GND
GND
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
= VCC[V]  ICC[A] + Iout[A]  (VM[V] - VRNF[V] - Iout[A]  Rm[Ω]) (Linear Constant-Current Drive block)
VIN
VIN
50μA
V
V
2
[A
2
]  RON[Ω] (Full-ON Drive block and PWM Constant-Current Drive block)
By using the diode temperature characteristics of the control input pin, on a
channel that is not driven, the junction temperature X can be measured in a
pseudo manner.
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] =
13/15
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
-2 [mV/°C]
a - b[mV]
+ 25[°C]
Technical Note
2009.06 - Rev.A
･･････(2)
･･････(3)
･･････(4)