参数资料
| 型号： | TPS81256SIPR |
| 厂商： | Texas Instruments |
| 文件页数： | 13/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST SYNC 5V 0.6A 9USIP |
| 标准包装： | 1 |
| 类型： | 升压（升压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 5V |
| 输入电压： | 2.5 V ~ 5.5 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 4MHz |
| 电流 - 输出： | 600mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 9-VBGA |
| 包装： | 标准包装 |
| 供应商设备封装： | 9-uSIP（2.6x2.9） |
| 其它名称： | 296-30558-6 |
SLVSAZ9A – JUNE 2012 – REVISED AUGUST 2013
CURRENT LIMIT OPERATION, MAXIMUM OUTPUT CURRENT
The TPS8125x directly and accurately controls the average input current through intelligent adjustment of the
valley current limit. The current limit circuit employs a valley current sensing scheme. Current limit detection
occurs during the off-time by sensing of the voltage drop across the synchronous rectifier.
The output voltage is reduced as the power stage of the device operates in a constant current mode. The
maximum continuous output current (I OUT(CL) ), before entering current limit (CL) operation, can be defined by
I OUT(DC) =I IN(CL) g
V OUT
V IN
g h
(1)
The output current, I OUT(DC) , is the average of the rectifier ripple current waveform. When the load current is
increased such that the lower peak is above the current limit threshold, the off-time is increased to allow the
current to decrease to this threshold before the next on-time begins (so called frequency fold-back mechanism).
When the current limit is reached the output voltage decreases during further load increase.
SOFTSTART, ENABLE
The TPS8125x device starts operation when EN is set high and starts up with the soft-start sequence. For proper
operation, the EN pin must be terminated and must not be left floating.
The TPS8125x device has an internal softstart circuit that limits the inrush current during start-up. The first step
in the start-up cycle is the pre-charge phase. During pre-charge, the rectifying switch is turned on until the output
capacitor is charged to a value close to the input voltage. The rectifying switch is current limited (approx. 200mA)
during this phase. This mechanism is used to limit the output current under short-circuit condition.
Once the output capacitor has been biased to the input voltage, the converter starts switching. The soft-start
system progressively increases the on-time as a function of the input-to-output voltage ratio. As soon as the
output voltage is reached, the regulation loop takes control and full current operation is permitted.
Pulling the EN pin low forces the device in shutdown, with a shutdown current of typically 1μA. In this mode, true
load disconnect between the battery and load prevents current flow from V IN to V OUT , as well as reverse flow
from V OUT to V IN .
LOAD DISCONNECT AND REVERSE CURRENT PROTECTION
Regular boost converters do not disconnect the load from the input supply and therefore a connected battery will
be discharge during shutdown. The advantage of TPS8125x is that this converter is disconnecting the output
from the input of the power supply when it is disabled (so called true shutdown mode). In case of a connected
battery it prevents it from being discharge during shutdown of the converter.
UNDERVOLTAGE LOCKOUT
The under voltage lockout circuit prevents the device from malfunctioning at low input voltages and the battery
from excessive discharge. It disables the output stage of the converter once the falling V IN trips the under-voltage
lockout threshold V UVLO which is typically 2.0V. The device starts operation once the rising V IN trips V UVLO
threshold plus its hysteresis of 100 mV at typ. 2.1V.
THERMAL REGULATION
The TPS8125x device contains a thermal regulation loop that monitors the die temperature during the pre-charge
phase. If the die temperature rises to high values of about 110 °C, the device automatically reduces the current
to prevent the die temperature from increasing further. Once the die temperature drops about 10 °C below the
threshold, the device will automatically increase the current to the target value. This function also reduces the
current during a short-circuit condition.
THERMAL SHUTDOWN
As soon as the junction temperature, T J , exceeds 140°C (typ.) the device goes into thermal shutdown. In this
mode, the high-side and low-side MOSFETs are turned-off. When the junction temperature falls below the
thermal shutdown minus its hysteresis, the device continuous the operation.
Copyright ? 2012–2013, Texas Instruments Incorporated
Product Folder Links: TPS81256
13
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