參數(shù)資料
型號: MIC2660
廠商: Micrel Semiconductor,Inc.
英文描述: IttyBitty Charge Pump
中文描述: IttyBitty電荷泵
文件頁數(shù): 5/8頁
文件大?。?/td> 93K
代理商: MIC2660
August 1999
5
MIC2660
MIC2660
Applications Information
Electromagnetic Interference
The 18MHz oscillator may cause interference to radio cir-
cuits. 0.01
μ
F bypass capacitors should be mounted close to
the IN and OUT terminals.
Low-Side MOSFET Charge-Pump Driver
A standard MOSFET requires approximately 15V to fully
enhance the gate for minimum R
DS
(on)
. Substituting a logic-
level MOSFET reduces the required gate voltage, allowing
an MIC2660 to be used as an low-side FET driver.
A 3V powered MIC2660 will fully enhance a
logic-level
N-channel MOSFET low-side switch, with a 5k gate pull-
down resistor, in less than 1ms after the enable pin rises
above 1.5V. The 1nF MOSFET gate capacitance will be
discharged to turn-off in less than 10ms after the enable pin
goes below 1.5V.
Micrel
Enable
IN
OUT
MIC2660
1
3
GND
2
+3V to +5V
EN
5
Load
Supply
R
LOAD
1μF
0.1μF
100k
Figure 1. Charge-Pump Driver
An MIC2660 boosts a 5V input to 9V–12V to fully enhance an
N-channel MOSFET, which may have its drain connected to
a higher voltage, through a high-side load. A TTL high signal
applied to CS enables the internal oscillator, which quickly
develops 9V–12V at the gate of the MOSFET, clamped by a
zener diode. A resistor from the gate to ground ensures that
the FET will turn off quickly when the MIC2660 is turned off.
Charge-Pump/Dump
A large capacitor can be charged to the
unloaded
tripled
voltage output after a time based on the maximum current
provided by the MIC2660. A 1000
μ
F Capacitor can be
charged from 2V to approximately 12V in less than 3 seconds
by a 5V powered MIC2660. (i = C dvdt).
Once charged, a maximum current of 3mA may be drawn
continuously at the 12V level. A high value bleeder resistor
(100k) is not needed to prevent spikes from exceeding the
capacitor voltage rating, since the MIC2660’s internal 15V
ESD zener limits maximum output. A 68
resistor in series
with the output limits short-circuit current to 30mA.
IN
OUT
MIC2660
1
3
GND
2
+5V
EN
5
+12V
1000μF
0.1μF
100k
68
Figure 2. Charge-Pump/Dump
5-Volt Lamp Flasher
An IttyBitty MIC1557 oscillator provides a short pulse once
per second, enabling the CS pin of an MIC2660, which
charges the gate-to-drain capacitance of a logic-level
N-channel MOSFET to approximately 9V, which turns on a
lamp. When the CS pin is low, a 2k resistor discharges the
gate capacitance, turning off the lamp. A resistor (R
S
) in
series with a diode determines the “on” time to approximately
R
S
||R
T
×
C
T
,while R
T
and C
T
set the “off” time to 1.1R
T
×
C
T
.
IN
OUT
MIC2660
1
3
GND
2
EN
5
VS
CS
MIC1557
4
3
GND
2
+5V
OUT
5
T/T
1
5V lamp
C
T
0.68μF
IRL3103
N-channel
FET
0.1μF
2k
R
S
470k
R
T
1M
Figure 3. 5-Volt Lamp Flasher
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