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| 型号： | LTC1929IG-PG#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 28-SSOP |
| 标准包装： | 47 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 360kHz |
| 占空比： | 99.5% |
| 电源电压： | 4 V ~ 36 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 ~ 85°C |
| 封装/外壳： | 28-SSOP（0.209"，5.30mm 宽） |
| 包装： | 管件 |
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LTC1929/LTC1929-PG
APPLICATIO S I FOR ATIO
EXTV CC Connection
The LTC1929 contains an internal P-channel MOSFET
switch connected between the EXTV CC and INTV CC pins.
When the voltage applied to EXTV CC rises above 4.7V, the
internal regulator is turned off and the switch closes,
connecting the EXTV CC pin to the INTV CC pin thereby
supplying internal and MOSFET gate driving power. The
switch remains closed as long as the voltage applied to
EXTV CC remains above 4.5V. This allows the MOSFET
driver and control power to be derived from the output
during normal operation (4.7V < V EXTVCC < 7V) and from
the internal regulator when the output is out of regulation
(start-up, short-circuit). Do not apply greater than 7V to
the EXTV CC pin and ensure that EXTV CC < V IN + 0.3V when
using the application circuits shown. If an external voltage
source is applied to the EXTV CC pin when the V IN supply is
not present, a diode can be placed in series with the
LTC1929’s V IN pin and a Schottky diode between the
EXTV CC and the V IN pin, to prevent current from backfeeding
V IN .
Significant efficiency gains can be realized by powering
INTV CC from the output, since the V IN current resulting
from the driver and control currents will be scaled by the
ratio: (Duty Factor)/(Efficiency). For 5V regulators this
means connecting the EXTV CC pin directly to V OUT . How-
ever, for 3.3V and other lower voltage regulators, addi-
tional circuitry is required to derive INTV CC power from the
output.
The following list summarizes the four possible connec-
tions for EXTV CC:
1. EXTV CC left open (or grounded). This will cause INTV CC
to be powered from the internal 5V regulator resulting in
a significant efficiency penalty at high input voltages.
2. EXTV CC connected directly to V OUT . This is the normal
connection for a 5V regulator and provides the highest
efficiency.
3. EXTV CC connected to an external supply. If an external
supply is available in the 5V to 7V range, it may be used to
power EXTV CC providing it is compatible with the MOSFET
gate drive requirements.
4. EXTV CC connected to an output-derived boost network.
For 3.3V and other low voltage regulators, efficiency gains
can still be realized by connecting EXTV CC to an output-
derived voltage which has been boosted to greater than
4.7V but less than 7V. This can be done with either the
inductive boost winding as shown in Figure 5a or the
capacitive charge pump shown in Figure 5b. The charge
pump has the advantage of simple magnetics.
Topside MOSFET Driver Supply (C B ,D B ) (Refer to
Functional Diagram)
External bootstrap capacitors C B1 and C B2 connected to
the BOOST1 and BOOST2 pins supply the gate drive
voltages for the topside MOSFETs. Capacitor C B in the
Functional Diagram is charged though diode D B from
INTV CC when the SW pin is low. When the topside MOSFET
turns on, the driver places the C B voltage across the gate-
source of the desired MOSFET. This enhances the MOSFET
and turns on the topside switch. The switch node voltage,
OPTIONAL EXTV CC CONNECTION
5V < V SEC < 7V +
V IN
C IN
+
V IN
+
C IN
V IN
1N4148
V SEC
V IN
TG1
BAT85
0.22 μ F
BAT85
LTC1929
TG1
N-CH
+
1 μ F
LTC1929
N-CH
VN2222LL
BAT85
EXTV CC
SW1
BG1
T1
R SENSE
+
V OUT
C OUT
EXTV CC
SW1
BG1
L1
R SENSE
+
V OUT
C OUT
N-CH
PGND
1929 F05a
Figure 5a. Secondary Output Loop with EXTV CC Connection
16
N-CH
PGND
Figure 5b. Capacitive Charge Pump for EXTV CC
1929 F05b
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