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參數(shù)資料
| 型號(hào)： | UC1914 |
| 廠商： | Texas Instruments, Inc. |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | 5V to 35V Hot Swap Power Manager |
| 中文描述： | 5V至35V的熱插拔電源管理器 |
| 文件頁(yè)數(shù)： | 12/14頁(yè) |
| 文件大?。?/td> | 652K |
| 代理商： | UC1914 |
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12
UC1914
On each complete cycle, CP1 is charged to approxi-
mately V
CC
– V
DIODE
(unless V
CC
is greater than 15V
causing internal clamping to limit this charging voltage to
about 13V) when the output Q of the toggle flip flop is
low. When Q is transitioned low (and Q correspondingly
is brought high), the negative side of CP2 is pulled to
ground, and CP1 charges CP2 up to about (2 V
CC
– 3
V
DIODE
). When Q is toggled high, the negative side of
CP2 is brought to (V
CC
–V
DIODE
). Since the voltage
across a capacitor cannot change instantaneously with
time, the positive side of the capacitor swings up to (3
V
CC
– 4 V
DIODE
). This charges C
PUMP
up to (3 V
CC
–
5 V
DIODE
).
The maximum output voltage of the linear amplifier is ac-
tually less than this because of the ability of the amplifier
to swing to within approximately 1V of V
PUMP
. Due to in-
efficiencies of the charge pump, the UC3914 may not
have sufficient gate drive to fully enhance a standard
power MOSFET when operating at input voltages below
7V. Logic Level MOSFETs could be used depending on
the application but are limited by their lower current capa-
bility. For applications requiring operation below 7V there
are two ways to increase the charge pump output volt-
age. Fig. 7 shows the typical tripler of Fig. 6 enhanced
with three external schottky diodes. Placing the schottky
diodes in parallel with the internal charge pump diodes
decreases the voltage drop across each diode thereby
increasing the overall efficiency and output voltage of the
charge pump.
Fig. 8 shows a way to use the existing drivers with exter-
nal diodes (or Schottky diodes for even higher pump
voltages but with additional cost) and capacitors to make
a voltage quadrupler. The additional charge pump stage
will provide a sufficient pump voltage (V
PUMP
= 4 V
CC
–
7 V
DIODE
) to generate the maximum V
GS
. Operation is
similar to the case described above. This additional cir-
cuitry is not necessary for higher input voltages because
the UC3914 has internal clamping which only allows
V
PUMP
to be 10V greater than V
OUTS
.
Input
Voltage
(VCC)
Internal
Diodes
(V
GS
)
External
Schottky
Diodes (V
GS
)
6.8
7.9
8.6
8.8
8.8
9
9.4
9.4
Quadrupler
(V
GS
)
4.5
5
5.5
6
6.5
7
9
10
4.57
5.8
6.6
7.6
8.7
8.8
9.2
9.3
8.7
8.8
8.9
9
9
9
9.1
9.3
Table 1. UC3914 charge pump characteristics.
Table 1 characterizes the UC3914 charge pump in its
standard configuration, with external schottky diodes,
and configured as a voltage quadrupler. Please note:
The voltage quadrupler is unnecessary for input voltages
above 7.0V due the internal clamping action.
ICC Specification
The ICC operating measurement is actually a mathe-
matical calculation. The charge pump voltage is con-
stantly being monitored with respect to both V
CC
and
V
OUTS
to determine whether the pump requires servic-
ing. If there is insufficient voltage on this pin, the charge
pump drivers are alternately switched to raise the volt-
age of the pump (see Fig. 9). Once the voltage on the
pump is high enough, the drivers and other charge pump
related circuitry are shutdown to conserve current. The
pump voltage will decay due to internal loading until it
reaches a low enough level to turn the drivers back on.
The chip requires significantly different amounts of cur-
rent during these two modes of operation and the follow-
ing mathematical calculation is used to figure out the
average current:
ICC
T
DRIVERS on
ON
=
ICC
ICC
T
T
T
DRIVERS off
OFF
ON
OF
+
+
(
)
(
)
F
APPLICATION INFORMATION (cont.)
8
7
5
6
CP2
Q
Q
250kHz
OSCILLATOR
TOGGLE
FLIP FLOP
9
2
D1
D2
D3
C
PUMP
TO VOUT
VPUMP
OSCB
CP1
OSC
T
VCC
PMP
PMPB
Figure 7. Enhanced charge pump block diagram.
UDG-98204
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