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參數(shù)資料
| 型號(hào)： | TCL1585 |
| 廠商： | TelCom Semiconductor, Inc. |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | 7A / 5A / 4.6A / 3A, FAST RESPONSE, LOW DROPOUT POSITIVE LINEAR VOLTAGE REGULATORS |
| 中文描述： | 第7A / 5A條/ 4.6a進(jìn)入/ 3A條，響應(yīng)速度快，低壓降線性穩(wěn)壓器陽性 |
| 文件頁數(shù)： | 5/13頁 |
| 文件大?。?/td> | 144K |
| 代理商： | TCL1585 |
5
TCL1584
TCL1585
TCL1587
PRELIMINARY INFORMATION
7A / 5A / 4.6A / 3A, FAST RESPONSE,
LOW DROPOUT POSITIVE LINEAR
VOLTAGE REGULATORS
TCL1584/1585/1587-04 6/6/97
APPLICATIONS
General
The TCL158x family of devices combine high current
output (up to 7A) with low dropout voltage and built-in fault
protection in a traditional three-terminal LDO format. All
three device types are available in fixed output voltage and
adjustable output versions. Fault protection includes short-
circuit current limit, over-temperature limit, and safe-operat-
ing-area (SOA) governing.
These devices are pin-compatible upgrades for the
1083/1084/1085 family of LDO’s. However, the TCL158x
family delivers lower dropout voltage, faster load transient
response and improved internal frequency compensation.
Maximum supply voltage rating is 7.0V.
Modern processors cycle load current from near zero to
several amps in a time period measured in tens of nanosec-
onds. Load step response requirements are worsened by
tighter output voltage tolerances. The TCL1584/85/87 fam-
ily of regulators meets these stringent requirements without
an obnoxious amount of output capacitance, saving both
board space and cost.
Stability and Transient Response
Like most low dropout voltage regulators, the TCL158x
devices require the use of output capacitors to maintain
stability. Normally a 22
μ
F solid tantalum or a 100
μ
F alumi-
num electrolytic unit will ensure stability over all operating
conditions. Keep in mind that commercially available ca-
pacitors can have significant non-ideal
effects such as
capacitance value tolerance, temperature coefficient, ESR,
ESL. The TCL158x devices are optimized for use with low
ESR (<1
) capacitors.
On the adjustable voltage versions, bypassing the ADJ
pin will improve ripple rejection and transient response. This
is discussed in the Ripple Rejectionsection. This bypassing
increases the required output capacitance value. The previ-
ously suggested minimum values (22
μ
F and 100
μ
F) take
this into account. If no bypassing is used, lower values of
output capacitance may be used.
Transient regulation is directly related to output capaci-
tance value. For applications which require large load cur-
rent step changes, it is recommended that large output
capacitors (>100
μ
F) be used. The value of the output
capacitor can be increased without limit and will only im-
prove transient regulation.
In a typical high-performance microprocessor applica-
tion, the sudden transients can be so fast that the output
decoupling network must handle the sudden current de-
mand until the internal voltage regulator is able to respond.
In this case the non-ideal effects of the output capacitor are
critical in determining the regulator’s response. Output volt-
age response to step load current change is illustrated in
Figure 1. The capacitor’s ESR and ESL cause immediate
step changes in the output voltage. These are calculated as
follows:
V
ESR
=
I x ESR
DV
ESL
= DI/Dt x ESL
To reduce the initial voltage droop, one should select
low ESR and ESL capacitors. It should also be noted that the
ESR effect is multiplied by absolute change in load current
while the ESL effect is multiplied by the rate of changein load
current. After the initial voltage drop, the capacitor value
dominates the rate of change in voltage. This rate is calcu-
lated as follows:
V =
t x
I/C
Figure 1. Transient Load Voltage Response
ESR
EFFECTS
ESL
EFFECTS
POINT AT WHICH REGULATOR
TAKES CONTROL
CAPACITANCE
EFFECTS
SLOPE, t C
I
Typically high quality ceramic and tantalum capacitors
must be used in combination to minimize ESR and maximize
C. This decoupling network must also be placed close to the
microprocessor to reduce ESL (parasitic board trace induc-
tance). If possible, the capacitors should be placed inside
the microprocessor socket cavity. Of course, robust power
and ground planes will also improve performance by reduc-
ing parasitic voltage drops.
The TCL1584 has an adaptive current limiting scheme
where to ensure SOA for the output transistor, the current
limit is reduced for increasing input to output differential. This
means that the TCL1584 exhibits a negative resistance
characteristicunder certain conditions. This is a common
technique in LDO design to ensure SOA - especially LDO’s
with high maximum input voltage ratings. This negative
resistance can interact with the external capacitance and
inductance and cause oscillations during current limit. This
effect is highly dependent on system parameters and is
difficult to predict. However this oscillation, if it occurs, will
not damage the regulator and can be ignored if the system
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| TCL1585-3.3CAB | 7A / 5A / 4.6A / 3A, FAST RESPONSE, LOW DROPOUT POSITIVE LINEAR VOLTAGE REGULATORS |
| TCL1585-3.3CEB | 7A / 5A / 4.6A / 3A, FAST RESPONSE, LOW DROPOUT POSITIVE LINEAR VOLTAGE REGULATORS |
| TCL1587 | 7A / 5A / 4.6A / 3A, FAST RESPONSE, LOW DROPOUT POSITIVE LINEAR VOLTAGE REGULATORS |
| TCL1587-3.3CAB | 7A / 5A / 4.6A / 3A, FAST RESPONSE, LOW DROPOUT POSITIVE LINEAR VOLTAGE REGULATORS |
| TCL1587-3.3CEB | 7A / 5A / 4.6A / 3A, FAST RESPONSE, LOW DROPOUT POSITIVE LINEAR VOLTAGE REGULATORS |
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