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参数资料
| 型号： | TPS54226PW |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 稳压器 |
| 封装： | PACKAGE-14 |
| 文件页数： | 18/20页 |
| 文件大小： | 501K |
| 代理商： | TPS54226PW |
I
=
OUT(LL)
1
-
=
(V
-V
) V
IN
OUT
2 L
fws
V
IN
-
Tss(ms)=
C6(nF) Vref
Iss( A)
=
C6(nF) 0.765
2
www.ti.com
SLVSA14B – OCTOBER 2009 – REVISED JUNE 2010
At the beginning of each cycle, the high-side MOSFET is turned on. This MOSFET is turned off after internal one
shot timer expires. This one shot is set by the converter input voltage, VIN, and the output voltage, VO, to
maintain a pseudo-fixed frequency over the input voltage range, hence it is called adaptive on-time control. The
one-shot timer is reset and the high-side MOSFET is turned on again when the feedback voltage falls below the
reference voltage. An internal ramp is added to reference voltage to simulate output ripple, eliminating the need
for ESR induced output ripple from D-CAP2 mode control.
PWM Frequency and Adaptive On-Time Control
TPS54226 uses an adaptive on-time control scheme and does not have a dedicated on board oscillator. The
TPS54226 runs with a pseudo-constant frequency of 700 kHz by using the input voltage and output voltage to
set the on-time one-shot timer. The on-time is inversely proportional to the input voltage and proportional to the
output voltage, therefore, when the duty ratio is VOUT/VIN, the frequency is constant.
Light Load Eco-Mode Control
The TPS54226 is designed with Eco-Mode to increase light load efficiency . As the output current decreases
from heavy load condition, the inductor current is also reduced and eventually comes to point that its rippled
valley touches zero level, which is the boundary between continuous conduction and discontinuous conduction
modes. The rectifying MOSFET is turned off when its zero inductor current is detected. As the load current
further decreases the converter run into discontinuous conduction mode. The on-time is kept almost the same as
is was in the continuous conduction mode so that it takes longer time to discharge the output capacitor with
smaller load current to the level of the reference voltage. The transition point to the light load operation IOUT(LL)
current can be calculated in Equation 1.
(1)
Soft Start and Pre-Biased Soft Start
The soft start function is adjustable. When the EN pin becomes high, 2-mA current begins charging the capacitor
which is connected from the SS pin to GND. Smooth control of the output voltage is maintained during start up.
The equation for the slow start time is shown in Equation 2. VFB voltage is 0.765 V and SS pin source current is
2 mA.
(2)
A unique circuit to prevent current from being pulled from the output during startup if the output is pre-biased.
When the soft-start commands a voltage higher than the pre-bias level (internal soft start becomes greater than
feedback voltage VFB), the controller slowly activates synchronous rectification by starting the first low side FET
gate driver pulses with a narrow on-time. It then increments that on-time on a cycle-by-cycle basis until it
coincides with the time dictated by (1-D), where D is the duty cycle of the converter. This scheme prevents the
initial sinking of the pre-bias output, and ensure that the out voltage (VO) starts and ramps up smoothly into
regulation and the control loop is given time to transition from pre-biased start-up to normal mode operation.
Power Good
The power good function is activated after soft start has finished. The power good function becomes active after
1.7 times soft-start time. When the output voltage is within -10% of the target value, internal comparators detect
power good state and the power good signal becomes high. The power good output, PG, is an open drain
output. If the feedback voltage goes under 15% of the target value, the power good signal becomes low after a
10 ms internal delay.
Output Discharge Control
TPS54226 discharges the output when EN is low, or the controller is turned off by the protection functions (OVP,
UVP, UVLO and thermal shutdown). The output is discharged by an internal 50-
MOSFET which is connected
from VO to PGND. The internal low-side MOSFET is not turned on during the output discharge operation to
avoid the possibility of causing negative voltage at the output.
Copyright 2009–2010, Texas Instruments Incorporated
7
Product Folder Link(s): TPS54226
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| TPS54226RGTR | 功能描述:直流/直流开关转换器 4.5-18V Inp,2A Synch Step Down Converter RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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