FA7711V Datasheet, PDF (19/25 Pages) Fuji Electric – FUJI Power Supply Control IC

FA7711V
For CS3
ts3[ms] = R0 ⋅CCS3 ⋅ ln_⎜⎛ ^VCS3 _⎟⎞
⎝^{VCS3 −VCS3n} ⎠
R0 = ^R5⋅R6
R5+ R6
VCS3 = ^R6 ⋅VREF
R5+ R6
CCS1,CCS2,CCS3 :
Capacitance connected to CS* pin [μF]
R1 to R6 : Resistance connected to CS* pin [kΩ]
The output duty changes sharply around the
minimum and the maximum output duty. This
phenomenon occurs more conspicuously when
operating in a high frequency (i.e. when the pulse
width is narrow). Cautious care must be taken
when using high frequency.
（4）Pull-up/Pull-down resistor at the output
section
The power supply for control blocks of OUT pin
drivers is the VREF. The VREF voltage is not
operated at the condition of IC’s power supply VCC
below the UVLO voltage. Therefore, OUT* pins are
unstable at VCC below the UVLO voltage.
If you have this condition of VCC and possibility of
some trouble by unstable OUT* pins, connect pull up
or pull down resistor to OUT* pins. (Fig.12)
For Nch driven
VIN
VCC
18
VREF
PVCC
17
CTRL
OUT
9
GND
10
PGND
For Pch driven
VIN
VCC
18
VREF
PVCC
17
CTRL
OUT
（5）Restriction and recommended operating
conditions of external discrete component
To achieve a stable operation of the IC, the value of
external discrete components connected to VCC,
PVCC, VREF, CS, CP pins should be within the
recommended operating conditions. And the voltage
and the current applied to each pin should be also
within the recommended operating conditions.
If the pin voltage of OUT1, OUT2, or VREG
becomes higher than the VCC pin voltage, the
current flows from the pins to the VCC pin because
parasitic three diode exist between the VCC pin and
these pins. Be careful not to allow this current to flow.
（6）Performance of output stage
The performance of output stages is the sink
current (peak) of 800mA of and the source current
(peak) of -800mA.
Switching speed is effected by external switching
device, especially at high frequency, so examine the
external switching device and frequency carefully.
If the performance of the ICs is not sufficient for your
design, consider adding a buffer circuit to improve
the performance.
（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 ICCOP, 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*(ICCop+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)
ICCOP=7mA for VCC=12V in the case of a typical IC
from the characteristics curve. Qg=10nC,
fsw=560kHz, the IC loss ”Pd” is as follows.
Pd≒12*(7mA+10nC*560kHz)≒151mW
if two MOSFETs are driven under the same
condition for 3 channels, Pd is as follows:
Pd≒12*{7mA+3*(10nC*560kHz)}=286mW
9
GND
10
PGND
Fig.12
Fuji Electric Systems Co., Ltd.
AN-060E Rev.1.0
19
Jun-2010
http://www.fujielectric.co.jp/fdt/scd/