参数资料
| 型号： | LT1680ISW#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM CM 16-SOIC |
| 标准包装： | 47 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 200kHz |
| 占空比： | 90% |
| 电源电压： | 4 V ~ 60 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 16-SOIC（0.295"，7.50mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1328 (CN2011-ZH PDF) |
LT1680
APPLICATIO S I FOR ATIO
I 2
? I
T1
S1 + S X
referred slope compensation. The LT1680, however, uses
a current limit scheme that is independent of the slope
I 1
S1
S2
S1
S2
compensation effects (Average Current Limiting). This
provides operation at any duty cycle with no reduction in
OSCILLATOR
current sourcing capability, provided ripple current peak
0
PERIOD
0
amplitude is less than 15% of the current limit value. For
5a
TIME
5b
1680 F05
example, if the converter is set up to average current limit
at 10A, as long as the peak inductor current is less than
Figure 5. Inductor Current at DC > 50% and
Slope Compensation Adjusted Signal
S1 + S X is greater than S2, this condition for subharmonic
oscillation no longer exists.
For boost topologies, the required additional current wave-
form slope, or “Slope Compensation,” follows the relation:
11.5A, duty cycles up to 90% can be achieved without
compromising the average current limit value.
1.45
1.40
1.35
S X ≥
( S1 )( 2 DC – 1 )
( 1 – DC )
1.30
1.25
For duty cycles less than 50% (DC < 0.5), S X is negative and
is not required. For duty cycles greater than 50%, S X takes
on values dependent on S1 and duty cycle. S1 is simply V IN /
1.20
1.15
L. This leads to a minimum inductance requirement for a
given V IN , duty cycle and slope compensation (S X ) of:
1.10
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
DUTY CYCLE
? ( )
? V IN ?
?
? S X ?
L MIN =
2 DC – 1
1 – DC
1680 F06
Figure 6. Maximum Peak Ripple Current (Normalized)
vs Duty Cycle for Average Current Limit
If an inductor smaller than the minimum required for
The LT1680 contains an internal slope compensation
ramp that has an equivalent current referred value of:
internal slope compensation (calculated above as L MIN ) is
desired, additional slope compensation is necessary. The
? R SENSE ?
? f O ?
S X = 0.084 ? ?
Amp/s
LT1680 provides this capability through the SL/ADJ pin.
This feature is implemented by referencing this pin via a
resistor divider from the 5V REF pin to ground. The addi-
where f O is oscillator frequency and R SENSE is the external
current sense resistor. This yields a minimum inductance
requirement of:
tional slope compensation will be affected at the point in
the oscillator waveform (at pin C T ) corresponding to the
voltage set by the resistor divider. Additional slope com-
pensation can be calculated using the relation:
( V IN )( R SENSE )( 2 DC – 1 )
[ ( 0 . 084 )( f O ) ( 1 ? DC ) ]
L MIN ≥
A down side of slope compensation is that, since the IC
S X =
( 2500 )( f O )
( R TH )( R SENSE )
Amp/s
servo loop senses an increase in perceived inductor cur-
rent, the internal current limit functions are affected such
that the maximum current capability of a regulator is
reduced by the same amount as the effective current
12
where R TH is the Thevenin resistance of the resistor
divider. Actual compensation will actually be somewhat
greater due to internal curvature correction circuitry that
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