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參數資料
| 型號： | TPS2551DRVR |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 電源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO6 |
| 封裝： | GREEN, PLASTIC, SON-6 |
| 文件頁數： | 9/32頁 |
| 文件大小： | 1402K |
| 代理商： | TPS2551DRVR |
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APPLICATION INFORMATION
INPUT AND OUTPUT CAPACITANCE
PROGRAMMING THE CURRENT-LIMIT THRESHOLD
www.ti.com ........................................................................................................................................ SLVS736B – FEBRUARY 2008 – REVISED NOVEMBER 2008
Input and output capacitance improve the performance of the device; the actual capacitance should be optimized
for the particular application. For all applications, a 0.01
F to 0.1F ceramic bypass capacitor between IN and
GND is recommended as close to the device as possible for local noise de-coupling. This precaution reduces
ringing on the input due to power-supply transients. Additional input capacitance may be needed on the input to
reduce voltage overshoot from exceeding the absolute maximum voltage of the device during heavy transients.
This is especially important during bench testing when long, inductive cables are used to connect the evaluation
board to the bench power-supply.
Placing a high-value electrolytic capacitor on the output pin is recommended when the large transient currents
are expected on the output. Additionally, bypassing the output with a 0.01
F to 0.1 F ceramic capacitor
improves the immunity of the device to short-circuit transients.
The overcurrent threshold is user programmable via an external resistor. Many applications require that the
minimum current-limit is above a certain current level or that the maximum current-limit is below a certain current
level, so it is important to consider the tolerance of the overcurrent threshold when selecting a value for RILIM.
The following equations and Figure 21 can be used to calculate the resulting overcurrent threshold for a given
external resistor value ILIM). Figure 21 includes current-limit tolerance due to variations caused by temperature
and process. The traces routing the RILIM resistor to the TPS2550/51should be as short as possible to reduce
parasitic effects on the current-limit accuracy.
There are two important current-limit thresholds for the device and are related by Figure 4. The first threshold is
the short-circuit current threshold IOS. IOS is the current delivered to the load if the part is enabled into a
short-circuit or a short-circuit is applied during normal operation. The second threshold is the overcurrent
threshold IOC. IOC is the peak DC current that can be delivered to the load before the device begins to limit
current. IOC is important if ramped loads or slow transients are common to the application. It is important to
consider both IOS and IOC when choosing RILIM. RILIM can be selected to provide a current-limit threshold that
occurs 1) above a minimum load current or 2) below a maximum load current.
To design above a minimum current-limit threshold, find the intersection of RILIM and the maximum desired load
current on the IOS(min) curve and choose a value of RILIM below this value. Programming the current-limit above a
minimum threshold is important to ensure start-up into full-load or heavy capacitive loads. The resulting
maximum DC load current is the intersection of the selected value of RILIM and the IOC(max) curve.
To design below a maximum DC current level, find the intersection of RILIM and the maximum desired load
current on the IOC(max) curve and choose a value of RILIM above this value. Programming the current-limit below a
maximum threshold is important to avoid current-limiting upstream power supplies causing the input voltage bus
to droop. The resulting minimum short-circuit current is the intersection of the selected value of RILIM and the
IOS(min) curve.
Overcurrent Threshold Equations (IOC):
I
OC(max) (mA) = (24500 V) / ILIM k)
0.975
I
OC(typ) (mA) = (23800 V) / ILIM k)
0.985
I
OC(min) (mA) = (23100 V) / ILIM k)
0.996
Short-Circuit Current Equations (IOS):
I
OS(max) (mA) = (25500 V) / ILIM k)
1.013
I
OS(typ) (mA) = (28700 V) / ILIM k)
1.114
I
OS(min) (mA) = (39700 V) / ILIM k)
1.342
where 14.3 k
≤ RILIM ≤ 80.6 k. IOS(typ) and IOS(max) are not plotted to improve graph clarity.
Copyright 2008, Texas Instruments Incorporated
17
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