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| 型号： | LT1952IGN#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 24/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR ISO PWM CM 16-SSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 560kHz |
| 占空比： | 90% |
| 电源电压： | 9.25 V ~ 25 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 ~ 125°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
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LT1952/LT1952-1
APPLICATIONS INFORMATION
Bus Converter: Optimum Output Voltage Tolerance
The Bus Converter applications shown on page 1 and in
Figure 16, provide semi-regulated isolated outputs without
the need for an optocoupler, optocoupler driver, reference or
feedback network. The LT1952/LT1952-1Volt-Second clamp
adjusts switch duty cycle inversely proportional to input
voltage to provide an output voltage that is regulated against
input line variations. Some bus converters use a switch duty
cycle limit which causes output voltage variation of typically
± 33% over a 2:1 input voltage range. The LT1952/LT1952-1
typically provide a ± 10% output variation for the same input
variation. Typical output tolerance is further improved for the
LT1952 by inserting a resistor from the system input voltage
to the SS_MAXDC pin (Rx in Figure 19).
The LT1952/LT1952-1 electrical specifications for the OUT
Max Duty Cycle Clamp show typical switch duty cycle to
move from 72% to 33% for a 2x change of input voltage
(SS_MAXDC pin = 1.84V). Since output voltage regulation
follows V IN ? Duty Cycle, a switch duty cycle change of
72% to 36% (for a 2x input voltage change) provides
minimal output voltage variation for the LT1952/LT1952-1
bus converter. To achieve this, an SS_MAXDC pin voltage
increase of 1.09x (36/33) would be required at high input
line. A resistor Rx inserted between the SS_MAXDC pin
and system input voltage (Figure 19) increases SS_MAXDC
voltage as input voltage increases, minimizing output
voltage variation over a 2:1 input voltage change.
The following steps determine values for Rx, R T and R B :
(1)Program switch duty cycle at minimum system input
voltage (V S(MIN) )
(a)R T(1) = 10k (minimum allowed to still guarantee soft-
start pull-down)
SYSTEM
INPUT VOLTAGE
(b)Select switch duty cycle for the Bus Converter for a
given output voltage at V S(MIN) and calculate SS_MAXDC
voltage (SS1) (See Applications Information “Program-
ming Maximum Duty Cycle Clamp”)
(c)Calculate R B(1) = [SS1/(2.5 – SS1)] ? R T(1)
(2)Calculate Rx:
Rx = ([V S(MAX) – V S(MIN) ]/[SS1 ? (X – 1)]) ? R THEV(1)
R THEV(1) = R B(1) ? R T(1) /(R B(1) + R T(1) ), X = ideal duty
cycle (V S(MAX) )/actual duty cycle (V S(MAX) )
(3)The addition of Rx causes an increase in the original
programmed SS_MAXDC voltage SS1. A new value for
R B(1) should be calculated to provide a lower SS_MAXDC
voltage (SS2) to correct for this offset:
(a)SS2 = SS1 – [(V S(MIN) – SS1) ? R THEV(1) /Rx]
(b)R B(2) = [SS2/(2.5 – SS2)] ? R T(1)
(4)The thevinin resistance R THEV(1) used to calculate Rx
should be re-established for R T and R B :
(a) R B (final value) = R B(2) ? (R THEV(1) /R THEV(2) )
(b) R T (final value) = R T(1) ? (R THEV(1) /R THEV(2) )
where R THEV(2) = R B(2) ? R T(1) /(R B(2) + R T(1) )
Example:
For a Bus Converter running from 36V to 72V input,
V S(MIN) = 36V, V S(MAX) = 72V.
choose R T(1) = 10k, SS_MAXDC = SS1 = 1.84V (for 72%
duty cycle at V S(MIN ) = 36V)
R B(1) = [1.84V/(2.5V – 1.84V)] ? 10k = 28k
R THEV(1) = [28k ? 10k/(28k + 10k)] = 7.4k
SS_MAXDC correction = 36%/33% = 1.09
Rx = [(72V – 36V)/(1.84 ? 0.09)] ? 7.4k = 1.6M
VOLT-SECOND
CLAMP INPUT
VOLT-SECOND
CLAMP ADJUST INPUT
R1
R2
Rx
R T
R B
LT1952/
LT1952-1
SD_V SEC
SS_MAXDC
V REF
1952 F19
SS2 = 1.84 – [(36V – 1.84) ? 7.4k/1.6M] = 1.682V
R B(2) = [1.682/(2.5 – 1.682)] ? 10k = 20.6k
R THEV(2) = [20.6k ? 10k/(20.6k + 10k)] = 6.7k
R THEV(1) /R THEV(2) = 7.4k/6.7k = 1.104
Figure 19. Optimal Programming of Maximum Duty
Cycle Clamp for Bus Converter Applications (Adding Rx)
R B (final value) = 20.6k ? 1.104 = 22.7k (choose 22.6k)
R T (final value) = 10k ? 1.104 = 11k
19521fe
24
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1952MPGN#PBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT1952MPGN#TRPBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT1952MPGN-1#PBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT1952MPGN-1#TRPBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 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 ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT1956 | 制造商:LINEAR 制造商全称:LINEAR 功能描述:100V Synchronous Switching Regulator Controller |
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