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参数资料
| 型号： | LTC3826IUH#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 21/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 32-QFN |
| 标准包装： | 73 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 585kHz |
| 占空比： | 99.4% |
| 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： | 32-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3826
APPLICATIONS INFORMATION
gate charge current, may be supplied by either the 5.25V
V IN LDO or the 7.5V EXTV CC LDO. When the voltage on
the EXTV CC pin is less than 4.7V, the V IN LDO is enabled.
Power dissipation for the IC in this case is highest and is
equal to V IN ? INTV CC . The gate charge current is depen-
dent on operating frequency as discussed in the Ef?ciency
Considerations section. The junction temperature can be
estimated by using the equations given in Note 2 of the
Electrical Characteristics. For example, the LTC3826 INTV CC
current is limited to less than 24mA from a 24V supply when
in the G package and not using the EXTV CC supply:
T J = 70°C + (24mA)(24V)(95°C/W) = 125°C
To prevent the maximum junction temperature from being
exceeded, the input supply current must be checked while
operating in continuous conduction mode (PLLIN/MODE
= INTV CC ) at maximum V IN .
When the voltage applied to EXTV CC rises above 4.7V, the
V IN LDO is turned off and the EXTV CC LDO is enabled. The
EXTV CC LDO remains on as long as the voltage applied to
EXTV CC remains above 4.5V. The EXTV CC LDO attempts
to regulate the INTV CC voltage to 7.5V, so while EXTV CC
is less than 7.5V, the LDO is in dropout and the INTV CC
voltage is approximately equal to EXTV CC . When EXTV CC
is greater than 7.5V up to an absolute maximum of 10V,
INTV CC is regulated to 7.5V.
Using the EXTV CC LDO allows the MOSFET driver and
control power to be derived from one of the LTC3826’s
supply reduces the junction temperature in the previous
example from 125°C to:
T J = 70°C + (24mA)(5V)(95°C/W) = 81°C
However, for 3.3V and other low voltage outputs, 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 5.25V regulator
resulting in an ef?ciency penalty of up to 10% at high
input voltages.
2. EXTV CC Connected directly to V OUT . This is the normal
connection for a 5V to 10V regulator and provides the
highest ef?ciency.
3. EXTV CC Connected to an External supply. If an external
supply is available in the 5V to 10V range, it may be
used to power EXTV CC providing it is compatible with
the MOSFET gate drive requirements.
4. EXTVCC Connected to an Output-Derived Boost Network.
For 3.3V and other low voltage regulators, ef?ciency
gains can still be realized by connecting EXTV CC to an
output-derived voltage that has been boosted to greater
than 4.7V. This can be done with the capacitive charge
pump shown in Figure 8.
switching regulator outputs (4.7V ≤ V OUT ≤ 10V) during
normal operation and from the V IN LDO when the output
is out of regulation (e.g., startup, short-circuit). If more
C IN
+
V IN
1μF
current is required through the EXTV CC LDO than is spec-
i?ed, an external Schottky diode can be added between the
LTC3826
V IN
BAT85
0.22μF
BAT85
EXTV CC and INTV CC pins. Do not apply more than 10V to
the EXTV CC pin and make sure than EXTV CC ≤ V IN .
Signi?cant ef?ciency and thermal gains can be realized
by powering INTV CC from the output, since the V IN cur-
rent resulting from the driver and control currents will be
EXTV CC
TG1
SW
BG1
N-CH
L1
VN2222LL
R SENSE
+
BAT85
V OUT
C OUT
scaled by a factor of (Duty Cycle)/(Switcher Ef?ciency). For
5V to 10V regulator outputs, this means connecting the
EXTV CC pin directly to V OUT . Tying the EXTV CC pin to a 5V
N-CH
PGND
Figure 8. Capacitive Charge Pump for EXTV CC
3826 F08
3826fc
21
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