A7442MP8VR [AITSEMI]
DC-DC CONVERTER/ BUCK HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS;
| 型号： | A7442MP8VR |
| 厂家： | 
AiT Semiconductor |
| 描述： | DC-DC CONVERTER/ BUCK HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS DC-DC转换器 |
| 文件： | 总20页 (文件大小：705K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
DESCRIPTION
FEATURES
AP7442 is a High Efficiency Synchronous DC-DC
Buck Converters with CV / CC modes, which can
output up to 4.2 A in a wide input range from 6 V to
36 V. The A7442 operates either in CV (Constant
Voltage) mode or CC (Constant Current) mode.
With the CV / CC mode, adjustable current limit and
output voltage, the A7442 is particularly suitable for
QC 2.0 / 3.0 (12V / 1.5A, 9V / 2A and 5V / 3A),
Type-C PD (5 V / 3 A) and Apple portable device
(5V / 2.4A) applications. The output voltage and CC
limit can be programed through the FB, CSP and
CSN pins respectively.
In order to achieve better EMI performance and
comply with Apple’s MFi standard, the switching
frequency was fixed at 130kHz. A7442 is capable to
operate in CC mode down to 3V output voltage to
protect the soft-short condition that is from the over
current of the portable device
A discharge circuitry is integrated to quickly and
reliably discharge output capacitors to avoid the
faulty voltage delivery in case of output over voltage
and ensure safe operation for QC 2.0 / 3.0
application. The hiccup mode output Under Voltage
Protection(UVP) can reduce the average input
current to 50mA. Features such as output cord
voltage drop compensation and low voltage drop
operation is especially suitable for car charger.
Wide Input Supply Voltage Range of 6V ~ 40V
Up to 4.2 A Output Current
Up to 95 % Efficiency
130kHz Fixed Switching Frequency
Internal Soft-start Circuitry
Compensation for Output Cord Voltage Drop
Input Under Voltage Lockout
Input Over Voltage Protection
Adjustable Constant Current Limit
Output Over Voltage Protection
Output Auto Discharge
Cycle by Cycle Peak Current Limit
Hiccup Mode Output UVP for Soft-short ≤ 3V
Thermal Shutdown
Available in PSOP8 Package
APPLICATION
Car Charger
Portable Charging Devices
CV / CC regulation DC / DC converter
TYPICAL APPLICATION
The A7442 is available in PSOP8 package.
ORDERING INFORMATION
Package Type
Part Number
A7442MP8R
A7442MP8VR
PSOP8
MP8
SPQ: 4,000pcs/Reel
V: Halogen free Package
R: Tape & Reel
Note
AiT provides all RoHS products
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
PIN DESCRIPTION
Top View
Pin #
1
Symbol
VIN
Function
Input Voltage Supply. Connect a decoupling capacitor between
VIN and GND pins with least distance.
Converter feedback input. Connect to the center point of the
output feedback resistors divider to program the output voltage.
Current Limit Negative Feedback pin. Kevin sensing from this pin
to the sensing resistor is recommended.
2
3
4
5
6
7
8
FB
CSN
CSP
CC
Current Limit Positive Feedback pin. Kevin sensing from this pin
to the sensing resistor is recommended.
Cable Compensation pin. Connect a resistor to output to adjust
wire compensation gain.
Internal 5V Power Supply. Connect a 100nF capacitor between
VCC
VCC and GND pins for stability and noise de-coupling;
Boot-Strap pin. Supply input for the gate drive circuit of high-side
NFET. Connect a 100nF capacitor between BST and SW pins.
Switch Node between high-side NFET and low-side NFET.
Connect this pin to the switching node of inductor.
Ground and Thermal Pad on the bottom of IC. Ground pin of
internal circuitry and Power Return Pin for Sync-NFET source
connection.
BST
SW
DAP(9)
GND
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
ABSOLUTE MAXIMUM RATINGS
VIN
-0.3V ~ 42V
-0.3V ~ (VIN + 0.2V) ≤ 42V
-0.3V ~ 6V
SW
BST to SW
CSP, CSN, CC
-0.3V ~ 14V
VCC, FB
-0.3V ~ 6V
ESD Rating (Human Body Model)
Package Thermal ResistanceNOTE2
θJA
±4kVNOTE1
50°C/W
-40°C
TJ, Min. Operating
TJ, Max. Operating
Storage Temperature
Lead Temperature (Soldering 10 sec.)
Internally Limited
-55°C ~ 150°C
260°C
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.
NOTE1: Tested and classified as Class 3A per ESDA/JEDEC JDS-001-2014.
NOTE2: Thermal Resistance is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test
board of JEDEC 51-3 thermal measurement standard.
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
ELECTRICAL CHARACTERISTICSNOTE3
VIN = 12V, TA = 25℃, unless otherwise noted.
Parameter
Input Supply Voltage
Input Voltage
Symbol
Conditions
Min.
6
Typ.
-
Max.
40
Unit
V
VIN
Input UVLO & OVP
Input UVLO Threshold
Input OVP Threshold
Input OVP Hysteresis NOTE4
Input Supply Current
Quiescent Current
VUVLO
VIN Rising
VIN Rising
4.0
36.5
-
4.4
39.5
2.5
4.8
V
V
V
VIN_OVP
-
-
VIN_OVPHYS VIN Falling
IQ
VFB = 1.5V
-
500
-
850
μA
(non-switching)
Output Voltage
Output Voltage Range
Feedback Voltage Threshold
Feedback Current
VOUT
VFB_TH
IFB
3.4
13.0
V
V
0.980 1.000 1.020
-
10
50
nA
V
CSP OVP Threshold
CSP OVP Hysteresis
Feedback OVP Threshold
Feedback OVP Threshold
Hysteresis
VCSP_OVP VCSP Rising
VCSP_HYS VCSP Falling
13.2
14.0
840
113
14.9
-
-
-
-
mV
%
VFB_OVP
VFB Rising, % of VFB_TH
VFB_HYS
VFB Falling, % of VFB_TH
VCSP Falling
-
2
-
%
CSP UVP Threshold
UVP Hiccup Interval NOTE4
VUVP
tUVP
2.62
-
3.00
0.7
3.31
-
V
s
R
CC = 18kΩ, ILOAD = 2.4A,
Cable Compensation Voltage
VCCOMP
-
200
-
mV
RS = 18mΩ
Auto Discharge Threshold
Auto Discharge Current
Oscillator
VTH_DIS
IDIS
% of VFB_TH
-
-
113
60
-
-
%
mA
Switching Frequency
Maximum Duty CycleNOTE4
fSW
ILOAD = 1A
109
-
130
99
160
-
kHz
%
DMAX
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
Parameter
Symbol
Conditions
Min.
Typ.
Max.
Unit
MOSFET
High Side MOSFET On
Resistance
RDS(ON)H
RDS(ON)L
ILEAK_H
-
-
-
-
52
52
-
-
-
mΩ
mΩ
μA
Low Side MOSFET On
Resistance
High-Side MOSFET Leakage
Current
VSW = 0 V
9
7
Low-Side MOSFET Leakage
Current
ILEAK_L
VSW = VIN
-
μA
Current Limit
High Side MOSFET Peak
Current LimitNOTE4
ILIM_HS
VOUT = 5V
-
7.5
-
A
RS = 15mΩ, VOUT = 5V
RS = 17mΩ, VOUT = 5V
RS = 17mΩ, VOUT = 9V
RS = 17mΩ, VOUT = 12V
3.832 4.067 4.265
3.381 3.588 3.763
2.262 2.442 2.633
1.572 1.769 1.951
A
A
A
A
Constant Current Limit
Threshold
ICS
Regulator
TA = 25°C,
VCC Regulator
VVCC_5
4.541 4.896 5.109
V
0 < ICC <5mA
VIN = 12V, VCC = 4.3 V,
TA = 25 °C
VCC Output Current
ICC_10
10
-
-
-
-
mA
Soft-start
Soft-start Time NOTE4
Thermal Shutdown
Thermal Shutdown
ThresholdNOTE4
tSS
1.6
ms
TSDN
-
-
165
40
-
-
°C
°C
Thermal Shutdown
HysteresisNOTE4
TSDNHYS
NOTE3: Specifications over temperature range are guaranteed by design and characterization.
NOTE4: Guaranteed by design and characterization only.
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
TYPICAL PERFORMANCE CHARACTERISTICS
All curves taken at VIN = 12 V, VOUT = 5 V, RS = 15mΩ with configuration in Typical Application Circuit for
High Current Output shown in this datasheet. TA = 25 °C, unless otherwise specified.
1.
3.
5.
Efficiency vs. Load Current, VOUT = 5V
Efficiency vs. Load Current, VOUT = 12V
VOUT Regulation vs. Load Current,
2.
4.
6.
Efficiency vs. Load Current, VOUT = 9V
Efficiency vs. Input Voltage
Cable Compensation Voltage vs. Load Current,
R
CC = 0, R1 = 100kΩ, RS = 0
RCC + R1 = 100kΩ
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
7.
CCM Switching Frequency vs. VIN, IOUT = 1A
8.
CCM Switching Frequency vs. Temperature
9.
Reference Voltage vs. Temperature
10. MOSFET RDS(ON) vs. Temperature
11. Constant Current Limit Threshold vs.
Temperature
12. Quiescent Current vs. VIN
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
13. Output CC/CV Curve, VIN = 24V, RCC = 0Ω
14. Power Up
15. Power Down
16. Load Transient
17. Continuous Mode Operation
18. Discontinuous Mode Operation
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
19. Short Circuit Protection
20. Short Circuit Protection
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
BLOCK DIAGRAM
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
DETAILED INFORMATION
Operation
The A7442 is a monolithic high efficiency synchronous buck converters with CV / CC modes. It utilizes
internal MOSFETs to achieve high efficiency and up to 4.2A output current in a wide input range from 6V to
36V. The output voltage and constant current limit can be programed through the FB, CSP and CSN pins
respectively. The A7442 is capable to operate in CC mode down to 3V output voltage to protect the soft-short
condition that is from the over current of the portable device.
With the slope compensated current mode PWM control, provides stable switching and cycle-by-cycle current
limit for excellent load and line responses and protection of the internal switches. During normal operation, the
internal main switch is turned on for a certain time to ramp up the inductor current at each rising edge of the
internal oscillator, and turned off when the peak inductor current is above the error voltage. The current
comparator limits the peak inductor current. Once the main switch is turned off, the synchronous rectifier will
be turned on immediately and stay on until either the inductor current decay to zero, as indicated by the zero
current comparator or the beginning of the next clock cycle.
Compensation for Output Cord Voltage Drop
In charger applications, the voltage drop across the output cord is significant in high current charging process.
In some cases, excessive voltage drop across the output cord will even extend the charging time if high
impedance output cord is used. The A7442 integrated a cable compensation function. When the output
current increases, the CC pin sinks current into the IC to increase the voltage drop across the resistor, RCC, in
order to increase the output voltage. The sinking current of the CC pin is proportional to the voltage across
CSP and CSN pins. Thus, the cable compensation function can increase the output voltage according to the
load. The increment of the voltage measured at CSP pin(VCSP) is called Cable Compensation
Voltage(VCCOMP). The value of RCC determines the gain of the cable compensation. After taking the
voltage drop across the sensing resistor, RS, the value of RCC can be calculated using Equation 1.
V
CCOMP
S -
RCC
=
(1)
(IOUT X
R
VOS)K
Where
RCC is the value of the resistor between CC pin and the node of the inductor.
CCOMP is the cable compensation voltage measured at the CSP pin.
OUT is the output current of the converter.
OS is the internal offset voltage which is equal to 3.3 mV
V
I
V
K is a constant which is equal to 279μ.
RS is the value of the sensing resistor.
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
Programmable CV / CC Mode Control
The A7442 features a CV / CC function. It operates either in CV mode or CC mode. The CV and the CC limits
can be programed through FB, CSP and CSN pins respectively. With the programmable output voltage and
constant current limit. The device is particularly suitable for QC 2.0, QC 3.0 Type-C PD and Apple portable
device applications.
The CC mode provides an accurate current limiting function which is programed through the sensing resistor,
RS. Output current can increase until it reaches the CC limit set by the sensing resistor. At this point, the
A7442 will transit from regulating output voltage to regulating output current, and the output voltage will drop
with increasing load. The A7442 can output up to 4.2A current at 5V output voltage. In general, 3A output
current is sufficient for charging purpose at 5 V output voltage. Figure 1 shows the CC limit verse sensing
resistor, RS. In this case, the CC limit should be set at a level which is about 10% higher than 3A. A 18mΩ
sensing resistor should be selected for ensuring 3A continuous output current. The CC limit is adaptive at
different output voltages which is particularly useful in QC 2.0 / 3.0 application.
Figure 1. Constant Current Limit vs. Sensing Resistor
In CV mode, the feedback voltage is regulated at 1V and the output voltage is programed by the feedback
divider RCC, R1 and R2. RCC and R1 together form the upper feedback resistor and R2 is the lower feedback
resistor. The output voltage at no load can be calculated using Equation 2.
(RCC + R
1
) + R
2
VOUT
=
(2)
R2
where
V
OUT is the output voltage at no load.
R
CC is the value of the resistor between CC pin and the node of the inductor.
R1 is the value of the resistor between CC and FB pins.
R2 is the value of the resistor between FB and GND pins.
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
Cycle by Cycle Peak Current Limit
The peak current limit prevents the A7442 from high inductor current and drawing excessive current from the
input voltage rail. Excessive current might occur with a shorted or saturated inductor or a heavy load or a
shorted output circuit condition. If the inductor current reaches the peak limit threshold, the high-side
MOSFET is turned off and the low-side MOSFET is turned on to ramp down the inductor current.
Output Auto Discharge
The A7442 is designed for working with USB Interface IC (QC 2.0 / 3.0). Regarding to the output voltage
changing capability of this application, the A7442 integrates an output auto discharge path to discharge the
output capacitor at 60mA typically once the voltage at the FB pin raise above 113% of feedback voltage
threshold. The function is crucial in high voltage charging scheme.
For instant, the output capacitor is charged-up by the high voltage which is set by the portable device. After
the portable device is unplugged, the output capacitor takes time to be discharged if there is no high current
discharge path. There is a chance that a conventional 5V portable device is damaged by a high voltage once
it is connected to the power supply immediately after the detachment of QC 2.0 / 3.0 portable device.
Input Under-voltage Lockout(UVLO)
An input UVLO circuit prevents the converter from starting the operation until the input voltage rises above the
typical UVLO threshold of 4.4V.
Input Over Voltage Protection(OVP)
The input OVP is an additional function to protect the device from damage in a condition which is above the
specified input voltage range. Once the input voltage is raising above input OVP threshold, 39.5V typically,
the A7442 stops switching to reduce the chance of damage by the voltage spike at SW pin. The device goes
back to normal operation until the input voltage falls a hysteresis about 2.5V below the input OVP threshold.
Output Over Voltage Protection(OVP)
There are two individual output OVP functions in the A7442. Those are CSP OVP and FB OVP. The CSP
OVP senses the output voltage directly. If the voltage at CSP pin is detected above CSP OVP threshold of
14V(typ.), the device stops switching immediately until the voltage at the CSP pin drops the hysteresis voltage
lower than CSP OVP threshold. This function prevents the device as well as the output capacitors from
damage by high voltage on the output even though the feedback resistors are faulty opened.
The operation of FB OVP is very similar to the CSP OVP except that it detects the voltage of the FB pin(VFB).
Once VFB raises above 113% of the feedback voltage threshold, the FB OVP will be triggered immediately
and stop switching. This OVP condition will be remove until VFB drop 2% lower than FB OVP threshold.
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
Hiccup Mode Output Under Voltage Protection(UVP)
There is a CSP UVP threshold. If the threshold is hit, the hiccup mode output UVP will be triggered by
disabling the converter and restarts soft-start after a predefined interval about 0.7s. The A7442 repeats this
mode until the under voltage condition is removed. This function prevents the damage of the system from
hard-short condition and a soft-short condition from the over current of portable device.
Soft-start
The A7442 implements the soft-start function to reduce the inrush current during startup. The soft-start begins
once the input voltage raises above typical UVLO threshold of 4.4V. The soft-start time is typically 1.6ms.
Thermal Shutdown
A thermal shutdown is implemented to prevent the damage due to excessive heat and power dissipation.
Typically, the thermal shutdown happens at the junction temperature of 165°C. When the thermal shutdown is
triggered, the device stops switching until the junction temperature drops the hysteresis temperature lower
than thermal shutdown threshold, then the device starts switching again.
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
APPLICATIONS INFORMATION
Design Requirement
Design Parameters
Input Voltage Range
Typical Input Voltage
Output Voltage
Target Values
6V to 40V
24V
5V
Output Current Rating
VCCOMP at Full Load
3.5A
250mV
Table 1. Design Parameters
Setting the CC Limit
The simplified application circuit is showed on the front page. Figure 1 shows the CC Limit at 5V output verse
RS. According to this figure, RS should be set at around 15mΩ to output 3.5A continuous current.
Setting the Cable Compensation Resistor
The cable compensation resistor, RCC, determines the gain of the cable compensation. By subtitling VCCOMP
OUT, RS, VOS and K into the Equation 1, RCC = 18.21kΩ. 18kΩ is the closest E24 standard value. Table 2.
Shows the cable compensation voltage at different load with RCC = 18kΩ and RS = 15mΩ.
,
I
ILOAD (A)
VCCOMP (mV)
0
0.5
1
0
21
59
1.5
2
96
134
164
209
247
2.4
3
3.5
Table 2. Cable Compensation Voltage at Different Load
Setting the Output Voltage
The feedback resistors, R1 and R2, together with the cable compensation resistor, RCC, program the output
voltage at no load condition according to the Equation 2.
For QC 2.0 / 3.0 applications, the upper feedback resistor(RCC + R1) is fixed at 100kΩ generally for
compatibility. Thus, R1 = 100kΩ - 18kΩ = 82kΩ. By subtitling RCC, R1 and VOUT into the Equation 2, R2 = 25kΩ
(24.9kΩ is the closest standard value).
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A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
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40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
Inductor Selection
Since the selection of the inductor affects the power supply’s steady state operation, transient behavior, loop
stability, and overall efficiency, the inductor is the most important component in switch power regulator design.
Three most important specifications to the performance of the inductor are the inductor value, DC resistance,
and saturation current.
The A7442 designed to work with inductor values between 15μH to 47μH. A 15μH inductor is typically
available in a smaller or lower-profile package, while a 47μH inductor produces lower inductor current ripple. If
the output current is limited by the peak current limit of the IC, using a 47μH inductor can maximize the
converter’s output current capability.
The tolerance of inductors can be ranging from 10% to 30%. The inductance will further decrease 20% to
35% from the value of zero bias current depending on the definition of saturation by inductor manufacturers.
The basic requirements of selecting an inductor are the saturation current must be higher than the peak
switching current and the DC rated current is higher than the average inductor current in normal operation. In
buck converter, the average inductor current is equal to the output current. The inductor value can be derived
from the Equation 3.
(VOUT + VCCOMP) x (VIN - VOUT - VCCOMP
)
L=
(3)
V
IN X ∆
I x FSW
L
where
ΔIL is the inductor peak-to-peak ripple current.
V
OUT is the output voltage at no load.
CCOMP is the cable compensation voltage measured at the CSP pin.
V
VIN is the input voltage.
SW is the switching frequency
F
Lower inductor value results in higher ripple current and vice versa. Choose inductor ripple current
approximately 30% of the maximum load current, 3.5A, or ΔIL = 1.05A. By subtitling VIN(typ.), VOUT, ΔIL and
VCCOMP, ΔIL and FSW(typ.) into the above equation, the inductor value, L, is 31.3μH.
The common inductor value is 33μH.
The saturation current of the inductor must be higher than the maximum output current, 3.5A, plus half of the
inductor ripple current in the worst case, i.e. highest operating VIN(36V) lowest FSW(109kHz), lowest inductor
value(-10 ~ -30% from nominal value), to prevent the core from saturation. Table 3 lists a typical toroid
inductor specification that meets target application for the design requirement.
Core
Core Part
Number
No. of Wire Ø
AL
(nH/N2)
Size[ODxIDxH]
(mm)
L(μH)
μ
Manufacturer
KDM Magnetic
Powder Cores
Turns
(mm)
KS040-125A 33 ±10%
23
0.7
125
66
10.20x5.08x3.96
Table 3. Recommended Toroid Inductor
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DC-DC CONVERTER/ BUCK (STEP-DOWN)
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40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and the switching noise from the converter.
The input capacitor impedance at the switching frequency should be less than the input source impedance to
prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum
RMS current must be used. Multilayer Ceramic Capacitor(MLCC) with X5R or X7R dielectric is highly
recommended because of their low ESR, low temperature coefficients and compact size characteristics. A
22μF MLCC is sufficient for most of applications.
Output Capacitor Selection
The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability.
The output capacitor must have low impedance at the switching frequency. MLCC with X5R or X7R dielectric
Is recommended due to their low ESR, low temperature coefficients and compact size characteristics. The
output ripple, ΔVOUT, is determined by:
VOUTx (VIN - VOUT)
VIN X FSW X L
1
ΔVOUT
≤
x ESR +
(4)
8 x FSW x COUT
Layout Considerations
When doing the PCB layout, the following suggestions should be taken into consideration to ensure proper
operation of the A7442. These suggestions are also illustrated graphically in Figure 2 and Figure 3.
1. The power path including the GND trace, the SW trace and the VIN trace should be as short as possible,
direct and wide.
2. The FB pin should be connected directly to the center point of the output feedback resistors divider.
3. The resistor divider must be connected to the output capacitor and GND pin directly.
4. The input decoupling MLCC should be placed as close to the VIN and GND pins as possible and
connected to input power plane and ground plane directly. This capacitor provides the AC current to the
internal power MOSFET.
5. The power path between the output MLCC, C5, and the power inductor should be kept short and the other
terminal of the capacitor should connect to the ground plane directly to reduce noise emission.
6. Keep the switching node, SW, away from the sensitive FB node.
7. Keep the negative terminals of input capacitor and output capacitor as close as possible.
8. Use Kelvin sense connection techniques from the sensing resistor, Rs, pads directly to the CSP and CSN
pins to achieve accurate CC limit.
9. Use large copper plane and thermal vias for GND for the best heat dissipation and noise immunity.
REV1.0
- JUL 2017 RELEASED -
- 17 -
A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
Figure 2. Top Layer
Figure 3. Bottom Layer
Typical Application Circuit with USB Interface IC
Typical Application Circuit for High Current Output
REV1.0
- JUL 2017 RELEASED -
- 18 -
A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
PACKAGE INFORMATION
Dimension in PSOP8 (Unit: mm)
Millimeters
Inches
Symbol
Min
Max
Min
Max
A
A1
A2
b
1.300
0.000
1.350
0.330
0.170
4.700
3.050
3.800
5.800
2.160
1.700
0.100
1.550
0.051
0.000
0.053
0.013
0.007
0.185
0.120
0.150
0.228
0.085
0.067
0.004
0.061
0.020
0.010
0.201
0.132
0.157
0.244
0.093
0.510
0.250
5.100
3.350
4.000
6.200
2.360
c
D
D1
E
E1
E2
e
1.270 BSC
0.050 BSC
L
0.400
0°
1.270
8°
0.016
0°
0.050
8°
θ
REV1.0
- JUL 2017 RELEASED -
- 19 -
A7442
DC-DC CONVERTER/ BUCK (STEP-DOWN)
AiT Semiconductor Inc.
www.ait-ic.com
40V, 4.2A HIGH PERFORMANCE CV/CC QUICK CHARGER SYNCHRONOUS
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 server 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
- JUL 2017 RELEASED -
- 20 -
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