A7431A [AITSEMI]
DC-DC CONVERTER BUCK CC/CV;
| 型号： | A7431A |
| 厂家： | 
AiT Semiconductor |
| 描述： | DC-DC CONVERTER BUCK CC/CV DC-DC转换器 |
| 文件： | 总15页 (文件大小：378K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
DESCRIPTION
FEATURES
A7431A is a wide input voltage, high efficiency
CC/CV step-down DC/DC converter that operates
in either CV (Constant Output Voltage) mode or CC
(Constant Output Current) mode. A7431A provides
up to 3A output current at 230kHz switching
frequency.
A7431A eliminates the expensive, high accuracy
current sense resistor, making it ideal for battery
charging applications and adaptors with accurate
current limit. The A7431A achieves higher
efficiency than traditional constant current switching
regulators by eliminating its associated power loss
on the additional current sensing resistor.
42V Input Voltage Surge
36V Steady State Operation
Up to 3A Output Current
Output Voltage up to 12V
230kHz Switching Frequency
Up to 91% Efficiency
Stable with Low-ESR Ceramic Capacitors to
Allow Low-Profile Designs
230kHz Switching Frequency Eases EMI Design
Constant Current Control Without Additional
Current Sensing Resistor Improves Efficiency
and Lowers Cost.
Resistor Programmable Current Limit from 1.5A
to 3.5A
Up to 0.5V Excellent Cable Voltage Drop
Compensation
Protection features include cycle-by-cycle current
limit, thermal shutdown, and frequency foldback at
short circuit. A7431A are available in a PSOP8
package and require very few external devices for
operation.
±7.5% CC Accuracy
2% Feedback Voltage Accuracy
Advanced Feature Set
The A7431A is available in PSOP8 package.
Integrated Soft Start
Thermal Shutdown
Cycle-by-Cycle Current Limit
Available in PSOP8 Package
ORDERING INFORMATION
APPLICATION
Package Type
PSOP8
Part Number
A7431AMP8R
A7431AMP8VR
Car Charger/ Adaptor
Rechargeable Portable Devices
General-Purpose CC/CV Supply
MP8
V: Halogen free Package
R: Tape & Reel
Note
TYPICAL APPLICATION
SPQ: 4,000pcs/Reel
AiT provides all RoHS products
Suffix “ V “ means Halogen free Package
REV1.0
- SEP 2016 RELEASED -
- 1 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
PIN DESCRIPTION
Top View
Pin #
1
Symbol
BS
Function
High Side Bias Pin. This provides power to the internal high-side MOSFET gate driver.
Connect a 22nF capacitor from BS pin to SW pin.
Power Supply Input. Bypass this pin with a minimum 10μF ceramic capacitor to GND,
placed as close to the IC as possible.
2
3
VIN
SW
Power Switching Output to External Inductor.
Ground. Connect this pin to a large PCB copper area for best heat dissipation. Return
FB, COMP, and ISET to this GND, and connect this GND to power GND at a single
point for best noise immunity.
4
GND
Feedback Input. The voltage at this pin is regulated to 0.808V. Connect to the resistor
divider between output and GND to set the output voltage.
5
6
FB
COMP
Error Amplifier Output. This pin is used to compensate the converter.
Enable Input. EN is pulled up to 5V with a 10μA current, and contains a precise 1.6V
logic threshold. Drive this pin to a logic-high or leave unconnected to enable the IC.
Drive to a logic-low to disable the IC and enter shutdown mode.
Output Current Setting Pin. Connect a resistor from ISET to GND to program the output
current.
7
EN
8
9
ISET
Exposed Heat Dissipation Pad. Connect this exposed pad to large ground copper area with
Pad copper and vias.
REV1.0
- SEP 2016 RELEASED -
- 2 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
ABSOLUTE MAXIMUM RATINGS
Input Supply Voltage
-0.3V ~ 42V
-1V ~ VIN + 1V
VSW - 0.3V ~ VSW + 7V
-0.3V ~ 6V
SW Voltage
Boost Voltage
All Other Pins Voltage
Junction to Ambient Thermal Resistance
Operating Junction Temperature
Storage Temperature
46°C/W
-40°C ~160°C
- 55°C ~ 150°C
- 40°C ~ 85°C
300℃
Operating Temperature
Lead Temperature (Soldering 10 sec.)
Stress beyond above listed “Absolute Maximum Ratings” may lead permanent damage to the device. These are stress ratings only and
operations of the device at these or any other conditions beyond those indicated in the operational sections of the specifications are not
implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
REV1.0
- SEP 2016 RELEASED -
- 3 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
ELECTRICAL CHARACTERISTICS
VIN = 20V, TA = +25℃, unless otherwise noted.
Parameter
Conditions
Min.
10
Typ.
Max.
36
Unit
V
Input Voltage
Input Voltage Surge
42
V
VIN UVLO Turn-On Voltage
VIN UVLO Hysteresis
Input Voltage Rising
Input Voltage Falling
VEN = 3V, VFB = 1V
VEN = 3V, VOUT = 5V,
No load
6
7
8
V
0.1
2.5
V
mA
Standby Supply Current
3
mA
Shutdown Supply Current
Feedback Voltage
VEN = 0V
10
808
3
μA
mV
ms
792
824
Internal Soft-Start Time
VFB = VCOMP = 0.8V,
Error Amplifier Transconductance
500
μA/V
ΔICOMP = ± 10μA
Error Amplifier DC Gain
4000
230
50
V/V
kHz
kHz
%
Switching Frequency
VFB = 0.808V
VFB = 0V
Foldback Switching Frequency
Maximum Duty Cycle
98
Minimum On-Time
200
4.2
ns
COMP to Current Limit Transconductance
Secondary Cycle-by-Cycle Current Limit
Slope Compensation
VCOMP = 1.2V
VOUT=3.5V
A/V
A
4.5
Duty = DMAX
1.2
A
ISET Voltage
1
V
ISET to IOUT DC Room Temp Current Gain
IOUT / ISET, RISET = 11.5kΩ
RISET = 22kΩ, VIN=14V,
27500
A/A
CC Controller DC Accuracy
VOUT = 3.5V
1250
mA
Open-Loop DC Test
EN Pin Rising
EN Shutdown Threshold Voltage
1.2
20
V
mV
V
EN Shutdown Threshold Voltage Hysteresis EN Pin Falling
EN Lockout Threshold Voltage
EN Lockout Hysteresis
EN Pin Rising
EN Pin Falling
1.47
1.6
125
10
1.73
10
mV
μA
Ω
EN Internal Pull-up Current
High-Side Switch ON-Resistance
SW Off Leakage Current
0.12
1
VEN = VSW = 0V
μA
°C
°C
Thermal Shutdown Temperature
Temperature Rising
160
40
Thermal Shutdown Temperature Hysteresis Temperature Falling
REV1.0
- SEP 2016 RELEASED -
- 4 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
BLOCK DIAGRAM
REV1.0
- SEP 2016 RELEASED -
- 5 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
DETAILED INFORMATION
Functional Description
CV/CC Loop Regulation
As seen in Functional Block Diagram, the A7431A is a peak current mode pulse width modulation (PWM)
converter with CC and CV control. The converter operates as follows:
A switching cycle starts when the rising edge of the Oscillator clock output causes the High-Side Power
Switch to turn on and the Low-Side Power Switch to turn off. With the SW side of the inductor now connected
to VIN, the inductor current ramps up to store energy in the magnetic field. The inductor current level is
measured by the Current Sense Amplifier and added to the Oscillator ramp signal. If the resulting summation
is higher than the COMP voltage, the output of the PWM Comparator goes high. When this happens or when
Oscillator clock output goes low, the High-Side Power Switch turns off.
At this point, the SW side of the inductor swings to a diode voltage below ground, causing the inductor current
to decrease and magnetic energy to be transferred to output. This state continues until the cycle starts again.
The High-Side Power Switch is driven by logic using BS as the positive rail. This pin is charged to VSW + 5V
when the Low-Side Power Switch turns on. The COMP voltage is the integration of the error between FB input
and the internal 0.808V reference. If FB is lower than the reference voltage, COMP tends to go higher to
increase current to the output. Output current will increase until it reaches the CC limit set by the ISET resistor.
At this point, the device will transition from regulating output voltage to regulating output current, and the
output voltage will drop with increasing load.
The Oscillator normally switches at 230kHz. However, if FB voltage is less than 0.6V, then the switching
frequency decreases to 50kHz gradually.
Enable Pin
The A7431A has an enable input EN for turning the IC on or off. The EN pin contains a precision 1.6V
comparator with 125mV hysteresis and a 10μA pull-up current source. The comparator can be used with a
resistor divider from VIN to program a startup voltage higher than the normal UVLO value. It can be used with
a resistor divider from VOUT to disable charging of a deeply discharged battery, or it can be used with a resistor
divider containing a thermistor to provide a temperature-dependent shutoff protection for over temperature
battery. The thermistor should be thermally coupled to the battery pack for this usage.
If left floating, the EN pin will be pulled up to roughly 5V by the internal 10μA current source. It can be driven
from standard logic signals greater than 1.6V, or driven with open-drain logic to provide digital on/off control.
Thermal Shutdown
The A7431A disables switching when its junction temperature exceeds 160°C and resumes when the
temperature has dropped by 40°C.
REV1.0
- SEP 2016 RELEASED -
- 6 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
APPLICATIONS INFORMATION
Output Voltage Setting
Figure 1: Output Voltage Setting
Figure 1 shows the connections for setting the output voltage. Select the proper ratio of the two feedback
resistors RFB1 and RFB2 based on the output voltage. Adding a capacitor in parallel with RFB1 helps the system
stability. Typically, use RFB2 ≈10kΩ and determine RFB1 from the following equation:
VOUT
0.808V
RFB1 = RFB2
−1
CC Current Setting
A7431A constant current value is set by a resistor connected between the ISET pin and GND. The CC output
current is approximating linearly proportional to the current flowing out of the ISET pin. The voltage at ISET is
roughly 1V and the current gain from ISET to output is roughly 27500 (27.5mA/1μA). To determine the proper
resistor for a desired current, please refer to Figure 2 below.
Figure 2: Curve for Programming Output CC Current
REV1.0
- SEP 2016 RELEASED -
- 7 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
Figure 3: CC/CV Curve（R3=11.5k, R8=52.3k, R2=10k）
Inductor Selection
The inductor maintains a continuous current to the output load. This inductor current has a ripple that is
dependent on the inductance value:
Higher inductance reduces the peak-to-peak ripple current. The trade off for high inductance value is the
increase in inductor core size and series resistance, and the reduction in current handling capability. In
general, select an inductance value L based on ripple current requirement:
V
OUT x (VIN − VOUT)
L =
V
IN
f
SW
I
LOADMAX RIPPLE
K
where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, ILOADMAX is the
maximum load current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 30% to correspond to the
peak-to-peak ripple current being 30% of the maximum load current.
With a selected inductor value the peak-to-peak inductor current is estimated as:
V
OUT x (VIN − VOUT)
L x VIN x fSW
ILPK-PK
The peak inductor current is estimated as:
=
1
ILPK = ILOADMAX
+
ILPK-PK
2
The selected inductor should not saturate at ILPK. The maximum output current is calculated as:
1
IOUTMAX = ILIM
-
ILPK-PK
2
ILIM is the internal current limit, which is typically 4.5A, as shown in Electrical Characteristics Table.
External High Voltage Bias Diode
REV1.0
- SEP 2016 RELEASED -
- 8 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
It is recommended that an external High Voltage Bias diode be added when the system has a 5V fixed input
or the power supply generates a 5V output. This helps improve the efficiency of the regulator. The High
Voltage Bias diode can be a low cost one such as IN4148 or BAT54.
Figure 4: External High Voltage Bias Diode
This diode is also recommended for high duty cycle operation and high output voltage applications.
Input Capacitor
The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the
converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor
during switching, its ESR also affects efficiency.
The input capacitance needs to be higher than 10μF. The best choice is the ceramic type, however, low ESR
tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50%
of the output current. The input capacitor should be placed close to the IN and GND pins of the IC, with the
shortest traces possible. In the case of tantalum or electrolytic types, they can be further away if a small
parallel 10μF ceramic capacitor is placed right next to the IC.
Output Capacitor
The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is:
VIN
VRIPPLE = IOUTMAXKRIPPLERESR
+
28 x fS2WLCOUT
Where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output
capacitor, fSW is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the
case of ceramic output capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower
capacitance value can be used for ceramic type. In the case of tantalum or electrolytic capacitors, the ripple is
dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have
sufficiently low ESR.
For ceramic output capacitor, typically choose a capacitance of about 22μF. For tantalum or electrolytic
capacitors, choose a capacitor with less than 50mΩ ESR.
Rectifier Diode
Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The Schottky
REV1.0
- SEP 2016 RELEASED -
- 9 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
diode must have current rating higher than the maximum output current and a reverse voltage rating higher
than the maximum input voltage.
STABILITY COMPENSATION
Figure 5: Stability Compensation
CCOMP2 is needed only for high ESR output capacitor The feedback loop of the IC is stabilized by the
components at the COMP pin, as shown in Figure 5.
The DC loop gain of the system is determined by the following equation:
0.808V
AVDC
=
AVEAGCOMP
I
OUT
The dominant pole P1 is due to CCOMP
:
G
EA
∫
=
P1
2πAVEA
C
COMP
The second pole P2 is the output pole:
I
OUT
∫
P2
=
2πVOUT
C
OUT
The first zero Z1 is due to RCOMP and CCOMP
:
1
∫
=
Z1
2πRCOMP
CCOMP
And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used):
1
∫
=
P3
2πRCOMPCCOMP2
The following steps should be used to compensate the IC:
STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP
:
REV1.0
- SEP 2016 RELEASED -
- 10 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
2πVOUT
C
OUT
f
SW
RCOMP
=
10GEA COMP x 0.808V
G
=5.12 x 107VOUTCOUT
(Ω)
STEP 2. Set the zero fZ1 at 1/4 of the cross over frequency. If RCOMP is less than 15kΩ, the equation for
COMP is:
C
2.83 x 105
RCOMP
CCOMP
=
(F)
If RCOMP is limited to 15kΩ, then the actual cross over frequency is 6.58 / (VOUTCOUT). Therefore:
CCOMP = 6.45 x 10-6VOUTCOUT
(F)
STEP 3. If the output capacitor’s ESR is high enough to cause a zero at lower than 4 times the cross over
frequency, an additional compensation capacitor CCOMP2 is required. The condition for using CCOMP2 is:
1.77x10−6
,0.006xVOUT
RESRCOUT
≥
Min
(Ω)
COUT
And the proper value for CCOMP2 is:
C
OUT
R
COMP
ESRCOUT
COMP2
=
R
Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 such
as 100pF may improve stability against PCB layout parasitic effects.
Table 1 shows some calculated results based on the compensation method above.
①
VOUT
COUT
RCOMP CCOMP CCOMP2
2.5V 47uF Ceramic CAP 5.6kΩ
3.3V 47uF Ceramic CAP 6.2kΩ
5.0V 47uF Ceramic CAP 12kΩ
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
None
None
None
47pF
47pF
47pF
2.5V 220uF/10V/30mΩ
3.3V 220uF/10V/30mΩ
5.0V 220uF/10V/30mΩ
20kΩ
20kΩ
20kΩ
CCOMP2 is needed for high ESR output capacitor.
COMP2 ≤ 47pF is recommended.
Table 1: Typical Compensation for Different Output Voltages and Output Capacitors
C
CC Loop Stability
The constant-current control loop is internally compensated over the 1500mA-3000mA output range. No
additional external compensation is required to stabilize the CC current.
REV1.0
- SEP 2016 RELEASED -
- 11 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
Output Cable Resistance Compensation
To compensate for resistive voltage drop across the charger's output cable, the A7431A integrates a simple,
user-programmable cable voltage drop compensation using the impedance at the FB pin. Use the curve in
Figure 6 to choose the proper feedback resistance values for cable compensation. RFB1 is the high side
resistor of voltage divider.
In the case of high RFB1 used, the frequency compensation needs to be adjusted correspondingly. As show in
Figure 7, adding a capacitor in paralleled with RFB1 or increasing the compensation capacitance at COMP pin
helps the system stability.
Figure 6: Cable Compensation at Various Resistor Divider Values
Figure 7: Frequency Compensation for High RFB1
REV1.0
- SEP 2016 RELEASED -
- 12 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
PC Board Layout Guidance
Figure8 showed the example of components placement and PCB layout. When laying out the printed circuit
board, the following checklist should be used to ensure proper operation of the IC.
1) Arrange the power components to reduce the AC loop size，consisting of input ceramic capacitor C1, VIN
pin, SW pin and the schottky diode D1.
2) Place input decoupling ceramic capacitor C1 as close to VIN pin as possible. C1 is connected power GND
with vias or short and wide path.
3) Return FB, COMP and ISET to signal GND pin, and connect the signal GND to power GND at a single
point for best noise immunity. Connect exposed pad to power ground copper area with copper and vias.
4) Use copper plane for power GND for best heat dissipation and noise immunity.
5) Place feedback resistor close to FB pin.
6) Use short trace connecting BS-C5-SW loop.
Figure 8: Example of PCB Layout
Figure 9. Typical Efficiency Curve
REV1.0
- SEP 2016 RELEASED -
- 13 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
PACKAGE INFORMATION
Dimension in PSOP8 (Unit: mm)
Symbol
Min
Max
A
A1
A2
b
1.400
0.050
1.350
0.330
0.170
4.700
3.202
3.800
5.800
2.313
1.700
0.150
1.550
0.510
0.250
5.100
3.402
4.000
6.200
2.513
c
D
D1
E
E1
E2
e
1.270(BSC)
L
0.400
0°
1.270
8°
θ
REV1.0
- SEP 2016 RELEASED -
- 14 -
A7431A
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
IMPORTANT NOTICE
AiT Semiconductor Inc. (AiT) reserves the right to make changes to any its product, specifications, to
discontinue any integrated circuit product or service without notice, and advises its customers to obtain the
latest version of relevant information to verify, before placing orders, that the information being relied on is
current.
AiT Semiconductor Inc.'s integrated circuit products are not designed, intended, authorized, or warranted to
be suitable for use in life support applications, devices or systems or other critical applications. Use of AiT
products in such applications is understood to be fully at the risk of the customer. As used herein may involve
potential risks of death, personal injury, or servere property, or environmental damage. In order to minimize
risks associated with the customer's applications, the customer should provide adequate design and
operating safeguards.
AiT Semiconductor Inc. assumes to no liability to customer product design or application support. AiT
warrants the performance of its products of the specifications applicable at the time of sale.
REV1.0
- SEP 2016 RELEASED -
- 15 -
相关型号：
©2020 ICPDF网 联系我们和版权申明