A7801 [AITSEMI]
DC-DC CONVERTER LOW NOISE, REGULATED CHARGE PUMP;
| 型号： | A7801 |
| 厂家： | 
AiT Semiconductor |
| 描述： | DC-DC CONVERTER LOW NOISE, REGULATED CHARGE PUMP DC-DC转换器 |
| 文件： | 总10页 (文件大小：266K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
DESCRIPTION
FEATURES
The A7801 is a low noise, constant frequency
(400kHz) switched capacitor voltage doubler. It
produce a regulated output voltage from a 2.5V to
5.5V input with up to 250mA of output current. Low
external parts count (one flying capacitor and two
small bypass capacitors at VIN and VOUT) make the
A7801 ideally suited for small, battery-powered
applications.
Fixed 5V ± 4% Output
VIN Range: 2.5V to 5.5V
Output Current: Up to 250mA
Constant Frequency Operation at All Loads
Low Noise Constant Frequency (400kHz)
Operation
Automatic Soft-Start Reduces Inrush Current
Shutdown Current <1uA
A
new charge-pump architecture maintains
Short-Circuit Protection
constant switching frequency to zero load and
reduces both output and input ripple. The A7801
have thermal shutdown capability and can survive a
continuous short circuit from VOUT to GND. Built-in
soft-start circuitry prevents excessive inrush current
during start-up.
No Inductors
Available in SOT-26 Package
APPLICATION
White LED Backlighting
Li-Ion Battery Backup Supplies
Local 3V to 5V Conversion
Smart Card Readers
High switching frequency enables the use of small
ceramic capacitors. A low current shutdown feature
disconnects the load from VIN and reduces
quiescent current to <1uA.
PCMCIA Local 5V Supplies
TYPICAL APPLICATION
The A7801 is available in SOT-26 package.
ORDERING INFORMATION
Package Type
SOT-26
Part Number
A7801E6R
E6
A7801E6VR
Figure 1. Basic Application Circuit with A7801
V: Halogen free Package
R: Tape & Reel
Note
AiT provides all RoHS products
Suffix “ V “ means Halogen free Package
REV1.0
- JAN 2015 RELEASED -
- 1 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
PIN DESCRIPTION
Top View
Pin #
1
Symbol
VOUT
Function
Regulated Output Voltage. VOUT should be bypassed with a low ESR ceramic
capacitor providing at least 2.2uF of capacitance as close to the pin as possible
for best performance.
2
3
4
GND
EN
Ground Pin.
Active Low Shutdown Input. This pin must not be allowed to float.
Flying Capacitor Negative Terminal.
C-
Input Supply Voltage. VIN should be bypassed with a low ESR ceramic capacitor
providing at least 2.2uF of capacitance as close to the pin as possible for best
performance.
5
6
VIN
C+
Flying Capacitor Positive Terminal.
REV1.0
- JAN 2015 RELEASED -
- 2 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
ABSOLUTE MAXIMUM RATINGS
VIN
-0.3V~+6V
-0.3V~5.5V
Indefinite
VOUT
VOUT Short-circuit Duration
VEN
-0.3V~+6V
300mA
NOTE1
IOUT
Operating Temperature Range NOTE2
Lead Temperature (Soldering 10 sec.)
Storage Temperature Range
-40°C~85°C
300°C
-65°C~125°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.
NOTE 1: Based on long term current density limitations.
NOTE 2: The A7801 are guaranteed to meet performance specifications from 0℃ to 70℃ Specifications over the –40℃ to 85 operating
temperature range are assured by design, characterization and correlation with statistical process controls.
ELECTRICAL CHARACTERISTICS
EN= VIN, CIN=COUT=10uF, TA = 25°C, Test Circuit of Figure 1, unless otherwise noted.
Parameter
Conditions
Min.
Typ.
Max.
5.5
Unit
V
Symbol
VIN
Input Voltage Range
2.5
2.7V <VIN < 5.5V,
Output Voltage Range
VOUT
4.7
5.0
5.2
V
IOUT < 65mA
Shutdown Current
No Load Input Current
Output Current Limit
Output Ripple
EN=0V,VOUT = 0V
0.3
0.65
250
150
81
μA
mA
VIN = 2.7V ,IOUT = 0mA
mA
VR
VIN = 2.7V , IOUT = 100mA
VIN = 2.7V , IOUT = 100mA
mVP-P
%
Efficiency
Open-Loop Output Resistance
ROL= (2VIN-VOUT)/IOUT
Switching Frequency
VIN = 2.7V , IOUT = 100mA
4.0
Ω
fOSC
400
kHz
REV1.0
- JAN 2015 RELEASED -
- 3 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
TYPICAL PERFORMANCE CHARACTERISTICS
Test Figure 1 above unless otherwise specified
1.
Output Voltage vs. Supply Voltage
2.
No Load Supply Current vs. Supply Voltage
3.
Oscillator Frequency vs. Supply Voltage
4.
η vs. IO
REV1.0
- JAN 2015 RELEASED -
- 4 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
BLOCK DIAGRAM
REV1.0
- JAN 2015 RELEASED -
- 5 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
DETAILED INFORMATION
Operation
The A7801 use a switched capacitor charge pump to boost VIN to a regulated output voltage. Regulation is
achieved by sensing the output voltage through an internal resistor divider and modulating the charge pump
output current based on the error signal. A 2-phase non overlapping clock activates the charge pump
switches. The flying capacitor is charged from VIN on the first phase of the clock. On the second phase of the
clock it is stacked in series with VIN and connected to VOUT. This sequence of charging and discharging the
flying capacitor continues at a free running frequency of 0.4MHz (typ). In shutdown mode all circuitry is turned
off and the A7801 draw only leakage current from the VIN supply. Furthermore, VOUT is disconnected from VIN.
The EN pin is a CMOS input with a threshold voltage of approximately 0.8V. The A7801 is in shutdown when
a logic low is applied to the EN pin. Since the EN pin is a high impedance CMOS input it should never be
allowed to float. To ensure that its state is defined it must always be driven with a valid logic level.
Short-Circuit Protection
The A7801 have built-in short-circuit current limiting. During short-circuit conditions, they will automatically
limit their output current to approximately 300mA.
Soft-Start
The A7801 have built-in soft-start circuitry to prevent excessive current flow at VIN during start-up. The
soft-start time is preprogrammed to approximately 1ms, so the start-up current will be primarily dependent
upon the output capacitor.
VIN, VOUT Capacitor Selection
The style and value of capacitors used with the A7801 determine several important parameters such as
regulator control loop stability, output ripple, charge pump strength and minimum start-up time. To reduce
noise and ripple, it is recommended that low ESR (< 0.1Ω) ceramic capacitors be used for both CIN and COUT
.
These capacitors should be 2.2uF or greater. Tantalum and aluminum capacitors are not recommended
because of their high ESR. The value of COUT directly controls the amount of output ripple for a given load
current. Increasing the size of COUT will reduce the output ripple at the expense of higher minimum turn on
time and higher start-up current. The peak-to-peak output ripple is approximately given by the expression:
REV1.0
- JAN 2015 RELEASED -
- 6 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
Where fOSC is the A7801 oscillator frequency (typically 0.4MHz) and COUT is the output charge storage
capacitor.
Both the style and value of the output capacitor can significantly affect the stability of the A7801. The A7801
use a linear control loop to adjust the strength of the charge pump to match the current required at the output.
The error signal of this loop is stored directly on the output charge storage capacitor.
The charge storage capacitor also serves to form the dominant pole for the control loop. To prevent ringing or
instability on the A7801 it is important for the output capacitor to maintain at least 2.2uF of capacitance over
all conditions.
Likewise excessive ESR on the output capacitor will tend to degrade the loop stability of the A7801.
Ceramic capacitors typically have exceptional ESR performance and combined with a tight board layout
should yield very good stability and load transient performance.
As the value of COUT controls the amount of output ripple, the value of CIN controls the amount of ripple
present at the input pin (VIN). The input current to the A7801 will be relatively constant while the charge pump
is on either the input charging phase or the output charging phase but will drop to zero during the clock non
overlap times. Since the non overlap time is small (~25ns), these missing “notches” will result in only a small
perturbation on the input power supply line. Note that a higher ESR capacitor such as tantalum will have
higher input noise due to the input current change times the ESR. Therefore ceramic capacitors are again
recommended for their exceptional ESR performance.
Flying Capacitor Selection
Warning: A polarized capacitor such as tantalum or aluminum should never be used for the flying capacitor
since its voltage can reverse upon start-up of the A7801. Low ESR ceramic capacitors should always be used
for the flying capacitor.
The flying capacitor controls the strength of the charge pump. In order to achieve the rated output current it is
necessary to have at least 2.2uF of capacitance for the flying capacitor.
For very light load applications the flying capacitor may be reduced to save space or cost. The theoretical
minimum output resistance of a voltage doubling charge pump is given by:
Where fOSC is the switching frequency (0.4MHz typ) and CFLY is the value of the flying capacitor. The charge
pump will typically be weaker than the theoretical limit due to additional switch resistance, however for very
REV1.0
- JAN 2015 RELEASED -
- 7 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
light load applications the above expression can be used as a guideline in determining a starting capacitor
value.
Power Efficiency
The power efficiency of the A7801 is similar to that of a linear regulator with an effective output voltage of
twice the actual input voltage. This occurs because the input current for a voltage doubling charge pump is
approximately twice the output current. In an ideal regulating voltage doubler the power efficiency would be
given by:
At moderate to high output power the switching losses and quiescent current of the A7801 are negligible and
the expression above is valid. For example with VIN = 3V, IOUT = 50mA and VOUT =5V the measured efficiency
is 80% which is in close agreement with the theoretical 83.3% calculation.
Layout Considerations
Due to its high switching frequency and the high transient currents produced by the A7801, careful board
layout is necessary. A true ground plane and short connections to all capacitors will improve performance and
ensure proper regulation under all conditions.
REV1.0
- JAN 2015 RELEASED -
- 8 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
PACKAGE INFORMATION
Dimension in SOT-26 (Unit: mm)
Symbol
Min
Max
A
A1
A2
b
1.050
0.000
1.050
0.300
0.100
2.820
1.500
2.650
1.250
0.100
1.150
0.500
0.200
3.020
1.700
2.950
c
D
E
E1
e
0.950(BSC)
e1
L
1.800
0.300
0°
2.000
0.600
8°
θ
REV1.0
- JAN 2015 RELEASED -
- 9 -
A7801
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
LOW NOISE, REGULATED CHARGE PUMP
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
- JAN 2015 RELEASED -
- 10 -
相关型号：
©2020 ICPDF网 联系我们和版权申明