MIC2660 Datasheet, PDF (5/8 Pages) Micrel Semiconductor – IttyBitty Charge Pump

MIC2660
Applications Information
Electromagnetic Interference
The 18MHz oscillator may cause interference to radio cir-
cuits. 0.01µF 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.
+3V to +5V
Load
Supply
100k
Enable
Disable
0.1µF
MIC2660
1
IN
3
OUT
5
EN
2
GND
R_LOAD
1µF
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.
Micrel
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 1000µF Capacitor can be
charged from 2V to approximately 12V in less than 3 seconds
by a 5V powered MIC2660. (i = C dv/dt).
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 68Ω resistor in series
with the output limits short-circuit current to 30mA.
+5V
100k
0.1µF
MIC2660
1
3 ^68Ω
IN
OUT
5
EN
2
GND
+12V
1000µF
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.
+5V
R_S 470k
R_T1MΩ
C_T
0.68µF
MIC1557
4 _VS
CS ³
1 _T/T
2 _GND
OUT ⁵
MIC2660
5V lamp
1 _IN
OUT ³
5 _EN
GND ²
2k
IRL3103
N-channel
FET
0.1µF
Figure 3. 5-Volt Lamp Flasher
August 1999
5
MIC2660