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| 型号： | ISL6742AAZA |
| 厂商： | Intersil |
| 文件页数： | 14/18页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR PWM CM/VM 16-QSOP |
| 标准包装： | 98 |
| PWM 型： | 电流/电压模式 |
| 输出数： | 4 |
| 频率 - 最大： | 2MHz |
| 占空比： | 100% |
| 电源电压： | 9 V ~ 16 V |
| 降压： | 无 |
| 升压： | 无 |
| 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 ~ 105°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1243 (CN2011-ZH PDF) |
ISL6742
Slope Compensation
Peak current-mode control requires slope compensation to
V n can be solved for in terms of input voltage, current
transducer components, and output inductance yielding
V e = ---------------------------------------- ? -------- ? --- + D – 0.5 ?
N P ? π
N CT ? L O
improve noise immunity, particularly at lighter loads, and to
prevent current loop instability, particularly for duty cycles
greater than 50%. Slope compensation may be accomplished
Equation 16:
t SW ? V O ? R CS N S 1
?
V
(EQ. 16)
by summing an external ramp with the current feedback signal
or by subtracting the external ramp from the voltage feedback
error signal. Adding the external ramp to the current feedback
signal is the more popular method.
From the small signal current-mode model [1] it can be
shown that the naturally-sampled modulator gain, F m ,
without slope compensation, is expressed in Equation 10:
where R CS is the current sense burden resistor, N CT is the
current transformer turns ratio, L O is the output inductance,
V O is the output voltage, and N S and N P are the secondary
and primary turns, respectively.
The current sense signal, which represents the inductor
current after it has been reflected through the isolation and
F m = --------------
1
S n S n
(EQ. 10)
current sense transformers, and passed through the current
sense burden resistor, is expressed in Equation 17:
N S ? R CS ? D ? t SW ? N S ? ?
N P ? N CT ?
V CS = ------------------------ ? I O + ------------------- ? V IN ? -------- – V O ? ?
where S n is the slope of the sawtooth signal and t SW is the
duration of the half-cycle. When an external ramp is added,
2L O ? N P ? ?
V
(EQ. 17)
the modulator gain becomes Equation 11:
F m = ------------------------------------ = --------------------------
m c = 1 + -------
1 1
( S n + S e ) t SW m c S n t SW
where S e is slope of the external ramp and:
S e
S n
(EQ. 11)
(EQ. 12)
where V CS is the voltage across the current sense resistor
and I O is the output current at current limit.
Since the peak current limit threshold is 1V, the total current
feedback signal plus the external ramp voltage must sum to
this value when the output load is at the current limit
threshold.
The criteria for determining the correct amount of external
ramp can be determined by appropriately setting the
V e + V CS = 1
(EQ. 18)
damping factor of the double-pole located at half the
oscillator frequency. The double-pole will be critically
Substituting Equations 16 and 17 into Equation 18 and
solving for R CS yields Equation 19:
R CS = ------------------------ ? ----------------------------------------------------
I O + -------- t SW ? --- + ---- ?
L ? π 2 ?
damped if the Q-factor is set to 1, over-damped for Q > 1,
and under-damped for Q < 1. An under-damped condition
may result in current loop instability.
N P ? N CT 1
N S V O 1 D
O
Ω
(EQ. 19)
Q = -------------------------------------------------
1
π ( m c ( 1 – D ) – 0.5 )
(EQ. 13)
For simplicity, idealized components have been used for this
discussion, but the effect of magnetizing inductance must be
where D is the percent of on-time during a half cycle (half
period duty cycle). Setting Q = 1 and solving for S e yields
Equation 14:
considered when determining the amount of external ramp
to add. Magnetizing inductance provides a degree of slope
compensation and reduces the amount of external ramp
required. The magnetizing inductance adds primary current
S e = S n ? ? --- + 0.5 ? ------------- – 1 ?
1 1
? ? π ? 1 – D ?
(EQ. 14)
in excess of what is reflected from the inductor current in the
secondary.
V IN ? Dt SW
Δ I P = -----------------------------
Since S n and S e are the on-time slopes of the current ramp
and the external ramp, respectively, they can be multiplied
L m
A
(EQ. 20)
by t ON to obtain the voltage change that occurs during t ON .
where V IN is the input voltage that corresponds to the duty
V e = V n ? ? --- + 0.5 ? ------------- – 1 ?
1 1
? ? π ? 1 – D ?
(EQ. 15)
cycle D and Lm is the primary magnetizing inductance. The
effect of the magnetizing current at the current sense
resistor, R CS , is expressed in Equation 21:
Δ I P ? R CS
Δ V CS = --------------------------
where V n is the change in the current feedback signal during
the on time and V e is the voltage that must be added by the
external ramp.
14
N CT
V
(EQ. 21)
FN9183.2
October 31, 2008
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| ISL6742AAZA-T | 功能描述:IC REG CTRLR PWM CM/VM 16-QSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:275kHz 占空比:50% 电源电压:18 V ~ 110 V 降压:无 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:是 工作温度:-40°C ~ 85°C 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) |
| ISL6744AABZ | 功能描述:IC REG CTRLR PWM VM 8-SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:275kHz 占空比:50% 电源电压:18 V ~ 110 V 降压:无 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:是 工作温度:-40°C ~ 85°C 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) |
| ISL6744AABZ-T | 功能描述:IC REG CTRLR PWM VM 8-SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:275kHz 占空比:50% 电源电压:18 V ~ 110 V 降压:无 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:是 工作温度:-40°C ~ 85°C 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) |
| ISL6744AAUZ | 功能描述:IC REG CTRLR PWM VM 8-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:275kHz 占空比:50% 电源电压:18 V ~ 110 V 降压:无 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:是 工作温度:-40°C ~ 85°C 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) |
| ISL6744AAUZ-T | 功能描述:IC REG CTRLR PWM VM 8-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:275kHz 占空比:50% 电源电压:18 V ~ 110 V 降压:无 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:是 工作温度:-40°C ~ 85°C 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) |
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