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参数资料
| 型号： | FA7704M |
| 厂商： | FUJI ELECTRIC CO LTD |
| 元件分类： | 稳压器 |
| 英文描述： | 0.4 A DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | SOP-16 |
| 文件页数： | 10/21页 |
| 文件大小： | 242K |
| 代理商： | FA7704M |
18
Quality is our message
FA7703/04
(7)Loss Calculation
Since it is difficult to measure IC loss directly,
the calculation to obtain the approximate loss of
the IC connected directly to a MOSFET is
described below.
When the supply voltage is VCC, the current
consumption of the IC is ICC1, the total input
gate charge of the driven MOSFET is Qg and
the switching frequency is fsw, the total loss Pd
of the IC can be calculated by:
Pd
≈ VCC ×(ICC1+Qg×fsw).
The value in this expression is influenced by
the effects of the dependency of supply voltage,
the
characteristics
of
temperature,
or
the
tolerance of parameter. Therefore, evaluate the
appropriateness
of
IC
loss
sufficiently
considering the range of values of above
parameters under all conditions.
Example)
ICC1=1.8mA for VCC=6.0V in the case of a
typical IC from the characteristics curve.
Qg=6nC, fsw=190kHz, the IC loss ”Pd” is as
follows.
Pd
≈ 6.0× (1.6mA+6nC×190kHz) ≈17.6mW
if two MOSFETs are driven under the same
condition for 2 channels, Pd is as follows:
Pd
≈ 6.0×{1.8mA+2× (6nC×190kHz)}=24.5mW
(8)Performance of output stage
The performance of the output stage of
FA7703/04 is the maximum sink current of
150mA and the maximum source current of
400mA.
The
switching
element
externally
attached to FA7703/04 might affect switching
speed of the ICs. Cautious care must be taken
about it especially in high frequency operation. If
the performance of the ICs is not sufficient for
your design, consider adding a buffer circuit to
improve the performance.
(9)In the case of bipolar driving
If using a bipolar transistor as the switching
element, there is a possibility of the damage
from burnout due to excessive current flow
because the ICs doesn’t contain an internal
limiter resistance. Therefore, be sure to install a
base resistor. (Fig. 11)
In the case of driving a
bipolar transistor, control the output current of
OUT
terminal
within
50mA(continuous)
in
operation. If you want to speed up the switching
speed, it is quite effective to install a capacitor
CB in addition.
(10)ON/OFF control
FA7703/04 can be turned ON/OFF at CS
terminal by external signal. The way to conduct
ON/OFF control is also shown in Fig. 12. When
the voltage of CS terminal is below the threshold
voltage, the duty becomes 0% and the output
turns OFF. The current consumption in this case
is 1.3mA(typ.). To switch the ICs ON, just turning
CS terminal open, then the soft start function
restarts, and the output turns back ON. ON/OFF
control at CS terminal is used for both channel,
and the control of each channel is not allowed.
10 8
9
7
Vcc
GND
OUT1
2
power supply
RB
CB
Fig.11
+
-
+
PW M.Com p
O scillation
output
CS term inal
voltage
DT term inal
voltage
Error Am plifier
output
12
7
2
+
-
+
DT term inal
voltage
6
Error Am plifier
output
ON/O FF
Fig.12
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