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參數(shù)資料
| 型號： | MAX1566-MAX1567 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Six-Channel, High-Efficiency, Digital Camera Power Supplies |
| 中文描述： | 六通道，高效率，數(shù)碼相機(jī)電源 |
| 文件頁數(shù)： | 28/35頁 |
| 文件大小： | 1134K |
| 代理商： | MAX1566-MAX1567 |
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M
Six-Channel, High-Efficiency, Digital
Camera Power Supplies
28
______________________________________________________________________________________
The inductor is typically selected to operate with contin-
uous current for best efficiency. An exception might be
if the step-up ratio, (V
OUT
/ V
IN
), is greater than 1 / (1 -
D
MAX
), where D
MAX
is the maximum PWM duty factor
of 80%.
When using the step-up channel to boost from a low
input voltage, loaded startup is aided by connecting a
Schottky diode from the battery to PVSU. See the
Minimum Startup Voltage vs. Load Current graph in the
Typical Operating Characteristics
.
Step-Up Inductor
In most step-up designs, a reasonable inductor value
(L
IDEAL
) can be derived from the following equation,
which sets continuous peak-to-peak inductor current at
1/2 the DC inductor current:
L
IDEAL
= [2V
IN(MAX)
x D(1 - D)] / (I
OUT
x f
OSC
)
where D is the duty factor given by:
D = 1 - (V
IN
/ V
OUT
)
Given L
IDEAL
, the consistent peak-to-peak inductor cur-
rent is 0.5 I
OUT
/ (1 - D). The peak inductor current,
I
IND(PK)
= 1.25 I
OUT
/ (1 - D).
Inductance values smaller than L
IDEAL
can be used to
reduce inductor size; however, if much smaller values
are used, inductor current rises and a larger output
capacitance may be required to suppress output ripple.
Step-Up Compensation
The inductor and output capacitor are usually chosen
first in consideration of performance, size, and cost. The
compensation resistor and capacitor are then chosen to
optimize control-loop stability. In some cases, it may
help to readjust the inductor or output-capacitor value to
get optimum results. For typical designs, the component
values in the circuit of Figure 1 yield good results.
The step-up converter employs current-mode control,
thereby simplifying the control-loop compensation.
When the converter operates with continuous inductor
current (typically the case), a right-half-plane zero
appears in the loop-gain frequency response. To
ensure stability, the control-loop gain should cross over
(drop below unity gain) at a frequency (f
C
) much less
than that of the right-half-plane zero.
The relevant characteristics for step-up channel com-
pensation are as follows:
Transconductance (from FB to CC), gm
EA
(135μS)
Current-sense amplifier transresistance, R
CS
(0.3V/A)
Feedback regulation voltage, V
FB
(1.25V)
Step-up output voltage, V
SU
, in V
Output load equivalent resistance, R
LOAD
, in
=
V
OUT
/ I
LOAD
The key steps for step-up compensation are as follows:
1) Place f
C
sufficiently below the right-half-plane zero
(RHPZ) and calculate C
C
.
2) Select R
C
based on the allowed load-step transient.
R
C
sets a voltage delta on the C
C
pin that corre-
sponds to load-current step.
3) Calculate the output-filter capacitor (C
OUT
) required
to allow the R
C
and C
C
selected.
4) Determine if C
P
is required (if calculated to be
>10pF).
For continuous conduction, the right-half-plane zero fre-
quency (f
RHPZ
) is given by the following:
f
RHPZ
= V
OUT
(1 - D)
2
/ (2
π
x L x I
LOAD
)
where D = the duty cycle = 1 - (V
IN
/ V
OUT
), L is the
inductor value, and I
LOAD
is the maximum output cur-
rent. Typically target crossover (f
C
) for 1/6 of the RHPZ.
For example, if we assume f
OSC
= 500kHz, V
IN
= 2.5V,
V
OUT
= 5V, and I
OUT
= 0.5A, then R
LOAD
= 10
. If we
select L = 4.7μH, then:
f
RHPZ
= 5 (2.5 / 5)
2
/ (2
π
x 4.7 x 10
-6
x 0.5) = 84.65kHz
Choose f
C
= 14kHz. Calculate C
C
:
C
C
= (V
FB
/ V
OUT
)(R
LOAD
/ R
CS
)(gm / 2
π
x f
C
)(1 - D)
= (1.25 / 5)(10 / 0.3) x [135μS / (6.28 x 14kHz)] (2/5)
= 6.4nF
Choose 6.8nF.
Now select R
C
so transient-droop requirements are
met. As an example, if 4% transient droop is allowed,
the input to the error amplifier moves 0.04 x 1.25V, or
50mV. The error-amp output drives 50mV x 135μS, or
6.75μA, across R
C
to provide transient gain. Since the
current-sense transresistance is 0.3V/A, the value of R
C
that allows the required load-step swing is as follows:
R
C
= 0.3 I
IND(PK)
/ 6.75μA
In a step-up DC-to-DC converter, if L
IDEAL
is used, out-
put current relates to inductor current by:
I
IND(PK)
= 1.25 I
OUT
/ (1 - D) = 1.25 I
OUT
x V
OUT
/ V
IN
So, for a 500mA output load step with V
IN
= 2.5V and
V
OUT
= 5V:
R
C
= [1.25(0.3 x 0.5 x 5) / 2)] / 6.75μA = 69.4k
Note that the inductor does not limit the response in this
case since it can ramp at 2.5V / 4.7μH, or 530mA/μs.
The output filter capacitor is then chosen so the C
OUT
R
LOAD
pole cancels the R
C
C
C
zero:
C
OUT
x R
LOAD
= R
C
x C
C
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1567ETL | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| MAX1567ETL+ | 功能描述:PMIC 解決方案 6Ch Digital Camera Power Supply RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| MAX1567ETL+T | 功能描述:PMIC 解決方案 6Ch Digital Camera Power Supply RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| MAX1567ETL-T | 功能描述:PMIC 解決方案 RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| MAX1567EVKIT | 制造商:Maxim Integrated Products 功能描述:6-CHANNEL HIGH EFFICIENCY DIGITAL CAMERA POWE - Bulk |
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