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参数资料
| 型号： | LTC1698EGN#TR |
| 厂商： | Linear Technology |
| 文件页数： | 15/24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： | 400kHz |
| 电源电压： | 6 V ~ 12.6 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： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | LTC1698EGNTR |
LTC1698
APPLICATIO S I FOR ATIO
P MAX ( Q 3 ) = I MAX ? R DS ( ON ) Q 3 ? DC ( Q 3 )
Iftheapplicationgeneratesabiggercurrentsensevoltage,
a potential divider can be easily obtained by adding a
resistor across C2. With this additional resistor, the volt-
age sensed by the current comparator becomes:
The R DS(ON) required for a given conduction loss can now
be calculated by rearranging the relation P = I 2 R.
2
R DIV
R DIV + ( 2 ? R 6 )
? V RSENSE
? R DS ( ON ) Q 3 =
P MAX ( Q 3 )
2
I MAX ? DC ( Q 3 )
P MAX ( Q 4 ) = I MAX DS ( ON ) Q 4 ? DC ( Q 4 )
? R DS ( ON ) Q 4 =
DC ( Q 3 ) =
V OUT N P
DC ( Q 4 ) = 1 – ? OUT ? P ?
AnRCnetworkformedbyR CILM andC CILM betweenI COMP
and V OUT can be used to stabilize the current limit loop.
Connecting the compensation network to V OUT minimizes
output overshoot during start-up or short-circuit recov-
ery. The R CILM and C CILM zero should be chosen to be well
within the closed-loop crossover frequency. This pin can
be left floating if current loop compensation is not re-
quired. The forward converter secondary current limit func-
tion can be disabled by shorting I SNS and I SNSGND to ground.
Auxiliary 3.3V Logic Power Supply
An internal P-channel LDO (low dropout regulator) pro-
duces the 3.3V auxiliary supply that can power external
devices or drive the MARGIN pin. This supply can source
up to 10mA of current and the current limit is provided
internally. The pin requires at least a 0.1 μ F bypass
capacitor.
MOSFET Selection
Two logic-level N-channel power MOSFETs (Q3 and Q4 in
Figure 1) are required for most LTC1698 circuits. They are
selected based primarily on the on-resistance and body
diode considerations. The required MOSFET R DS(ON) should
be determined based on input and output voltage, allow-
able power dissipation and maximum required output
current.
The average inductor (L1) current is equal to the output
load current. This current is always flowing through either
Q3 or Q4 with the power dissipation split up according to
the duty cycle:
?
V IN N S
? V N ?
? V IN N S ?
where N P /N S is the turns ratio of the transformer T1.
2
? R
P MAX ( Q 4 )
2
I MAX ? DC ( Q 4 )
where I MAX is the maximum load current and P MAX is the
allowable conduction loss.
In a typical 2-transistor forward converter circuit, the duty
cycle is less than 50% to prevent the transformer core
from saturating. This results in the duty cycle of Q4 being
greater than that of Q3. Q4 will dissipate more power due
to the higher duty cycle. A lower R DS(ON) MOSFET can be
used for Q4. This will slow down the turn-on time of Q4
since a lower R DS(ON) MOSFET will have a larger gate
capacitance.
The next consideration for the MOSFET is the characteris-
tic of the body diode. The body diodes conduct during the
power-up phase, when the LTC1698 V DD supply is ramp-
ing up and the time-out circuit is adapting to the SYNC
input frequency. The CG and FG signals terminate prema-
turely and the inductor current flows through the body
diodes. The body diodes must be able to take the compa-
rable amount of current as the MOSFETs. Most power
MOSFETs have the same current rating for the body diode
and the MOSFET itself.
The LTC1698 CG and FG MOSFET drivers will dissipate
power. This will increase with higher switching frequency,
higher V DD or larger MOSFETs. To calculate the driver
dissipation, the total gate charge Qg is used. This param-
eter is found on the MOSFET manufacturers data sheet.
The power dissipated in each LTC1698 MOSFET driver is:
P DRIVER = Qg ? V DD ? f SW
where f SW is the switching frequency of the converter.
1698f
15
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC1698ES | 功能描述:IC REG CTRLR ISO PWM CM 16-SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,000 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:50% 电源电压:9 V ~ 10 V 降压:无 升压:是 回扫:是 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:8-TSSOP（0.173"，4.40mm 宽） 包装:带卷 (TR) |
| LTC1698ES#PBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SOIC 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:2,000 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:50% 电源电压:9 V ~ 10 V 降压:无 升压:是 回扫:是 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:8-TSSOP（0.173"，4.40mm 宽） 包装:带卷 (TR) |
| LTC1698ES#TR | 功能描述:IC REG CTRLR ISO PWM CM 16-SOIC RoHS:否 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 |
| LTC1698ES#TRPBF | 功能描述:IC REG CTRLR ISO PWM CM 16-SOIC 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 |
| LTC1698IGN | 功能描述:IC REG CTRLR ISO PWM CM 16-SSOP RoHS:否 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 |
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