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参数资料
| 型号： | R1224N502F-TR |
| 英文描述： | Analog IC |
| 中文描述： | 模拟IC |
| 文件页数： | 6/36页 |
| 文件大小： | 503K |
| 代理商： | R1224N502F-TR |
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12345
Rev. 1.12 - 6 -
(2) Adjustable Output Type (R1224N102G/H/M) Example: Output Voltage=3.2V
C3
C2
L
C1
R1
SD
V
FB
V
IN
CE
CE CONTROL
LOAD
EXT
GND
C4
R2
R4
R3
PMOS
PMOS: HAT1044M (Hitachi) L: CR105-270MC (Sumida, 27
μ
H)
SD1: RB063L-30 (Rohm) C3: 47
μ
F (Tantalum Type)
C1: 10
μ
F (Ceramic Type) C2: 0.1
μ
F (Ceramic Type) C4: 1000pF(Ceramic Type)
R1: 10
, R2=22k
, R3=2.7k
, R4=33k
When you use these ICs, consider the following issues;
G
As shown in the block diagram, a parasitic diode is formed in each terminal, each of these diodes is not formed for
load current, therefore do not use it in such a way. When you control the CE pin by another power supply, do not
make its "H" level more than the voltage level of V
IN
pin.
G
Set external components as close as possible to the IC and minimize the connection between the components and
the IC. In particular, a capacitor should be connected to V
OUT
pin with the minimum connection. Make sufficient
ground and reinforce supplying. A large switching current could flow through the connection of power supply, an
inductor and the connection of V
OUT.
If the impedance of the connection of power supply is high, the voltage level of
power supply of the IC fluctuates with the switching current. This may cause unstable operation of the IC.
G
Protection circuit may work if the maximum duty cycle continue for the time defined in the electrical characteristics.
Once after stopping the output voltage, output will restart with soft-start operation. If the difference between input
voltage and output voltage is small, the protection circuit may work.
G
Use capacitors with a capacity of 22
μ
F or more for V
OUT
pin, and with good high frequency characteristics such as
tantalum capacitors. We recommend you to use output capacitors with an allowable voltage at least twice as much
as setting output voltage. This is because there may be a case where a spike-shaped high voltage is generated by
an inductor when an external transistor is on and off.
G
Choose an inductor that has sufficiently small D.C. resistance and large allowable current and is hard to reach
magnetic saturation. And if the value of inductance of an inductor is extremely small, the I
LX
may exceed the absolute
maximum rating at the maximum loading.
Use an inductor with appropriate inductance.
G
Use a diode of a Schottky type with high switching speed, and also pay attention to its current capacity.
G
Do not use this IC under the condition with V
IN
voltage at equal or less than minimum operating voltage.
G
When the threshold level of an external power MOSFET is rather low and the drive-ability of voltage supplier is
small, if the output pin is short circuit, input voltage may be equal or less than UVLO detector threshold. In this case,
the devise is reset with UVLO function that is different from the reset-protection function caused by maximum duty
cycle.
G
With the PWM/VFM alternative circuit, when the on duty cycle of switching is 35% or less, the R1225N alters from
PWM mode to VFM mode (Pulse skip mode). The purpose of this circuit is raising the efficiency with a light load by
skipping the frequency and suppressing the consumption current. However, the ratio of output voltage against input
voltage is 35% or less, (ex. Vin>8.6V and Vout=3.0V) even if the large current may be loaded, the IC keeps its VFM
mode. As a result, frequency might be decreased, and oscillation waveform might be unstable. These phenomena
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