YX605
NOUS STEP-UP CONVERTER FEATURES
?
Up to 0.9V Startup Voltage ?
Up to 94% Efficiency ?Internal Power Switch
? 3.3V and 5V Fixed or Adjustable Output Voltage
?Zero Supply Current Shutdown Mode ?
Tiny SOT 23-5 Package
APPLICATIONS
?Hand-Held Devices
?One to Three Cell Battery Operated Devices ?PDAs
?Cellular Phones ?Digital Cameras ?
GPS
GENERAL DESCRIPTION
The YX605 Low Input High Efficiency Synchronous Step-Up Converter is capable of delivering more than 400mA output current using only three external components.
Typical startup voltage is 0.95V and the device can operate down to a 0.6V input voltage.Incorporating an internal synchronous rectifier,the YX605 can achieve high efficiency of up to 94%. Variable switching frequency operation results in high efficiency for a wide range of loads.
The output voltage is selectable between 3.3V and 5V, or can be externally set to any voltage between 2V and 5V. The YX605 is available in the tiny SOT23-5 Package.
Figure 1. Typical Application Circuit
YX605LOW INPUT HIGH EFFICIENCY
SYNCHRONOUS STEP-UP CONVERTER
V1.0
华晶电子
手机：１８０ ０２５０ ８８５７，ＱＱ：１６６ ２５７ １９７３
ORDERING INFORMATION
PIN CONFIGURATION
PIN DESCRIPTION
OUT
LX
SOT23-5
ABSOLUTE MAXIMUM RATINGS
(Note: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.)
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V IN = 1.5V, V OUT = 3.3V, T A = 25°C unless otherwise specified.)
Figure 2. Functional Block Diagram
FUNCTIONAL DESCRIPTION
The YX605comprises a reference, feedback select error comparator, control logic and timers, internal power MOSFETs and current comparators. The Functional Block Diagram is shown in Figure 2.
MAIN CONTROL LOOP
The YX605uses the maximum ON time/minimum OFF time step-up architecture. An error comparator monitors the FB voltage. When FB is below the reference voltage and the 1μs minimum OFF time is exceeded, the latch is set and an ON cycle is initiated. During this period, the N-channel power switch is turned on to connect the LX node to ground. By doing so, the energy is transferred from supply to the inductor. Once the 5μs maximum ON time is exceeded or the 1A current limit is reached,the N-channel power switch is turned off and the OFF cycle begins. During OFF cycle the energy stored in the inductor is released into the load through the synchronous rectifier. After the minimum OFF time,if FB voltage drops below the reference voltage, the IC transitions to the ON cycle again. LIGHT LOAD OPERATION
At light load,the IC enters power-saving mode by extending the OFF time,resulting in high efficiency across a wide load range. START UP
The YX605uses a proprietary start-up scheme to ensure device start up at a very low supply voltage down to 0.95V. The device stays in the startup mode until V OUt passes 1.85V. During this start-up period,the maximum ON and minimum OFF times are extended. SHUTDOWN
In shutdown, all internal circuits are disabled. The power switch and the synchronous rectifier are turned off. A DC path from the input supply to the output still exists in shutdown due to the body diode of the synchronous rectifier when output is lower than input by one diode drop.
APPLICATION INFORMATION
OUTPUT VOLTAGE SELECTION
By connecting FB differently,three options are available for output voltages: fixed 3.3V, 5V or an adjustable voltage set by an external resistive divider. (Figure 3).
Figure 3.
OUTPUT CAPACITOR SELECTION
The output capacitor value should be in the range of22μF to100μ. A minimum value of capacitance is required to maintain loop stability and normal operation of the IC. To obtain small output ripple,use a large capacitor with low ESR.Ceramic capacitors should be used for highest performance. If a tantalum capacitor is used, choose only low ESR types. For a non-ceramic capacitors a smaller low ESR capacitor of about 1μF can be used in parallel to filter high frequency noise.
INDUCTOR SELECTION
The inductor value determines its ripple current. For most applications with this device, the inductor value should be in the range of 10μH to 47μH. Smaller inductors provide faster load transient response while having a smaller physical size.But they also generate higher ripple current,which reduces the maximum output current available to the load.Inductors with low series resistance are recommended to obtain highest efficiency.
BOARD LAYOUT
To reduce noise and increase efficiency, the traces for high current paths should be large and an extended ground plane used.
In order to reduce electromagnetic radiation, the switching current paths should be as short as possible.In other words,the input and output capacitors should be very close to the IC.
If the external resistor divider is used,it should be very close to the FB and G pins and the high switching current paths.
TYPICAL PERFORMANCE CHARACTERISTICS
NOUS STEP-UP CONVERTER YX605LOW INPUT HIGH EFFICIENCY
SYNCHRONOUS STEP-UP CONVERTER
V1.0
华晶电子
手机：１８０ ０２５０ ８８５７，ＱＱ：１６６ ２５７ １９７３
TYPICAL PERFORMANCE CHARACTERISTICS CONT'D
TYPICAL PERFORMANCE CHARACTERISTICS CONT'D
DCM Mode Connection
Low ESR Output Capacitor V OUT (50mV/Div)
V(LX) (2V/Div) Time: 5μs/Div V OUT
V(LX)
V OUT
= 3.3V V IN = 1.2V I LOAD
= 10mA
Current Limit Condition
Low ESR Output Capacitor V OUT (100mV/Div)
V(LX) (2V/Div) Time: 2.5μs/Div
V OUT
V(LX)
V OUT = 3.3V V IN = 2.4V I LOAD = 408mA Heavy Load Condition
Low ESR Output Capacitor V OUT (100mV/Div)
DCM Mode Connection
High ESR Output Capacitor V OUT (100mV/Div)
Heavy Load Condition
High ESR Output Capacitor V OUT (100mV/Div)
V OUT = 3.3V V IN
= 1.2V I LOAD = 10mA V OUT = 3.3V V IN = 2.4V I LOAD = 408mA
V(LX) (2V/Div) Time: 2.5μs/Div
V(LX) (2V/Div) Time: 25μs/Div
V(LX) (2V/Div) Time: 5μs/Div
V OUT
V(LX)
V OUT = 5.2V V IN = 3.6V I LOAD = 400mA
V OUT
V(LX)
V OUT = 3.3V V IN = 2.4V I LOAD = 340mA
V OUT
V(LX)
V OUT = 3.3V V IN = 2.4V I LOAD = 112mA
SOT23-5 PACKAGE OUTLINE AND DIMENSIONS