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PDF FA7700V Data sheet ( Hoja de datos )
| Número de pieza | FA7700V | |
| Descripción | For Switching Power Supply Control | |
| Fabricantes | ETC | |
| Logotipo |  |
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FA7700V, FA7701V
CMOS IC
For Switching PFoAw7e7r0S0uVp,pFlyAC7o7n0tr1oVl
s Description
FA7700V/FA7701V are the PWM type DC to DC converter
control ICs with 1ch output that can directly drive power
MOSFETs. CMOS devices with high breakdown voltage are
used in these ICs and low power consumption is achieved.
These ICs have not only the functions equivalent to those of
FA76XX series but also the functions of directly driving Nch/Pch
MOSFETs, lower power consumption, higher frequency
operation, and less external components.
s Features
• Wide range of supply voltage: VCC=2.5 to 20V
• FA7700V: For boost, flyback converter
(Maximum output duty cycle is 80%)
• FA7701V: For buck converter
(Maximum output duty cycle is 100%)
• Output stage consist of CMOS push-pull circuit, and achieves
a high speed switching of external MOSFETs. (FA7700V: For
Nch-MOSFET driving, FA7701V: For Pch-MOSFET driving)
• High accuracy reference voltage (Error amplifier): 0.88V±2%
• Soft start function
• Adjustable built-in timer latch for short-circuit protection
• Output ON/OFF control function
• Less external discrete components needed (2 components
less than conventional version of the equivalent products)
• Low power consumption
Stand-by current: 40µA typ.
Operating current: 1.2mA typ. (Including error amplifier output
current and oscillator current)
• High frequency operation: 50kHz to 1MHz
• Package: TSSOP-8, thin and small
s Dimensions, mm
TSSOP-8
0.575 typ
3.1±0.3
0.65
0.22 ±0.1
0.5 ±0.2
s Block diagram
FA7700V
FA7701V
RT 1
REF 2
IN– 3
FB 4
VREF
UVLO
0.3V
VREF
2.2V
OSC
BIAS
Power Good Signal
0.88V
+
–
ER.AMP
5.5V
1.5V
S.C.DET
1.5V +
–
ON/OFF
+
–
+
+
OFF
PWM
ON/OFF
–
+
S.C.P
+
–
2.2V
8 CS
7 VCC
6 OUT
5 GND
RT 1
REF 2
IN– 3
FB 4
UVLO
8 CS
VREF
0.3V ON/OFF
VREF
2.2V
OSC
BIAS
Power Good Signal
0.88V
+
–
ER.AMP
1.5V
S.C.DET
1.5V +
–
ON/OFF
+
–
+
OFF
PWM
–
+
S.C.P
+
7 VCC
–
2.2V 5.5V
6 OUT
5 GND
Pin No. Pin symbol Description
1 RT
Oscillator timing resistor
2 REF
Internal bias voltage
3 IN (–) Error amplifier inverting input
4 FB
Error amplifier output
5 GND
Ground
6 OUT
Output for driving switching device
7 VCC
Power supply
8 CS
ON/OFF, soft start, timer latched short
circuit protection
1
1 page  
s Characteristic curves
Oscillation frequency (fOSC) vs.
timing resistor resistance (RT)
10000
1000
100
10
1 10 100
Timing resisitor RT [kΩ]
Duty cycle vs. FB terminal voltage
FA7700
100
90
80
70
60 fosc=1MHz
50
40
30
fosc=185kHz
20
10
0
0.5 0.7 0.9
1.1 1.3
FB terminal voltage [V]
Duty cycle vs. FB terminal voltage
FA7701
100
90
80
70
fosc=1MHz
60
50
40
30
20
10
0
0.5
fosc=185kHz
0.7 0.9 1.1
FB terminal voltage [V]
1.3
FA7700V, FA7701V
Oscillation frequency (fOSC) vs. ambient temperature
5
4
3
2 fosc=1MHz
1
0
–1 fosc=50kHz
–2
fosc=185kHz
–3
–4
–5
–40
–20 0 20 40 60 80
Ambient temperature Ta [˚C]
100
Duty cycle vs. CS terminal voltage
FA7700
100
90
80
70
fosc=1MHz
60
50
40
30
20 fosc=185kHz
10
0
0.5 0.7 0.9 1.1 1.3
CS terminal voltage [V]
Duty cycle vs. CS terminal voltage
FA7701
100
90
80
70
fosc=1MHz
60
50
40
30
20
fosc=185kHz
10
0
0.5 0.7 0.9 1.1 1.3
CS terminal voltage [V]
5
5 Page 
FA7700V, FA7701V
You can reset the off latch mode operation of the short-circuit
protection by either of the following ways: lowering the CS
voltage below 2.03V (typ.); lowering the Vcc voltage below the
Off threshold voltage of undervoltage lock out; 1.93V (typ.);
lowering the voltage of FB terminal below 1.5V (typ.)
The off latch mode action cannot be triggered by externally
applying voltage of over 2.2V forcibly to the CS terminal (1.5V,
ZD clamped). Characteristics of the current and the voltage of
CS terminal is shown in the characteristic curve (CS terminal
voltage vs. CS terminal sink current) on page 6. Be sure to use
the IC up to the recommended CS terminal current of 50µA.
8. Output circuit
The IC contains a push-pull output stage and can directly drive
MOSFETs (FA7700: N ch, FA7701: P ch). The maximum peak
current of the output stage is a sink current of +150mA, and a
source current of –400mA. The IC can also drive NPN, and
PNP transistors. The maximum peak current in such cases is
±50mA. Be sure to design the output current considering the
rating of power dissipation.
9. Power good signal circuit/ Undervoltage lockout circuit
The IC contains a protection circuit against undervoltage
malfunctions to protect the circuit from the damage caused by
malfunctions when the supply voltage drops. When the supply
voltage rises from 0V, the circuit starts to operate at VCC of
2.07V (typ.) and outputs generate pulses. If a drop of the
supply voltage occurs, it stops output at VCC of 1.93V (typ.).
when it occurs, the CS terminal is turned to Low level and then
it is reset. The power good signal circuit monitors the voltage of
REF terminal, and stops output until the voltage of REF
terminal excesses approximately 2V to prevent malfunctions.
s Design advice
1. Setting the oscillation frequency
As described in item 2 “Oscillator” of “Description of each
circuit”, a desired oscillation frequency can be determined by
the value of the resistor connected to the RT terminal. When
designing an oscillation frequency, you can set any frequency
between 50kHz and 1MHz. You can roughly obtain the
oscillation frequency from the characteristic curve “Oscillation
frequency (fosc) vs. timing resistor resistance(RT)” or the value
can be calculated by the following expression.
fOSC = 3000 ϫ RT –0.9
( )RT = 3000 1.11
fOSC
fOSC: Oscillation frequency [kHz]
RT: Timing resistor [kΩ]
This expression, however, can be used for rough calculation,
the value obtained is not guaranteed. The operation frequency
varies due to the conditions such as tolerance of the
characteristics of the ICs, influence of noises, or external
discrete components. When determining the values, be sure to
verify the effectiveness of the values of the components in an
actual circuit.
2. Operation around the maximum or the minimum output
duties
As described in characteristic curves on page 5, “output duty
cycle vs. FB terminal voltage (VFB)” and “output duty cycle vs.
CS terminal voltage (Vcs)”, the linearity of the output duty of
this IC drops around the minimum output duty and the
maximum output duty (FA7701 only). This phenomena are
conspicuous when operating in a high frequency (when the
pulse width is narrow). Therefore be careful when using high
frequency.
3. Restriction of external discrete components
To achieve a stable operation of the ICs, the value of external
discrete components connected to Vcc, REF, CS, FB terminals
should be within the recommended operational conditions.
4. 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 Icc, the total input gate charge of the driven MOSFET is
Qg, the switching frequency is fsw, the total loss Pd of the IC
can be calculated by:
Pd Լ Vcc ϫ (Icc + Qg ϫ fsw).
The values in this expression is influenced by the effects of the
dependency of supply voltage, the characteristics of
temperature, or tolerance. Therefore, be sure to verify
appropriateness of the value considering the factors above
under all applicable conditions.
Example:
When VCC = 6V, in the case of a typical IC, from the
characteristic curve, Icc=1.2mA. When operating in Qg = 6nC,
fsw = 500kHz, Pd should be:
Pd Լ 6 ϫ (1.2mA + 6nC ϫ 500kHz) Լ 25.2mW
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet FA7700V.PDF ] | |
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