MAX679C/D 데이터 시트보기 (PDF) - Maxim Integrated
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MAX679C/D Datasheet PDF : 6 Pages
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Regulated 3.3V Charge Pump
____________________________Typical Operating Characteristics (continued)
(Typical Operating Circuit with: VIN = V SHDN = 2V, CIN = 4.7µF, C1 = 0.33µF, COUT = 10µF, tested in-circuit, TA = +25°C, unless
otherwise noted.)
OUTPUT RIPPLE (2mA LOAD)
MAX679 TOC10
FSET = IN (1MHz)
VOUT
50mV/div
AC COUPLED
100µs/div
LOAD-TRANSIENT RESPONSE
(1mA TO 10mA LOAD, VIN = 3V)
MAX679 TOC11
VOUT
10mV/div
AC COUPLED
VIN = 3V
FSET = IN (1MHz)
100µs/div
IOUT
5mA/div
LOAD-TRANSIENT RESPONSE
(1mA TO 10mA LOAD, VIN = 2V)
MAX679 TOC12
VOUT
10mV/div
AC COUPLED
VIN = 2V
FSET = IN (1MHz)
50µs/div
IOUT
5mA/div
______________________________________________________________Pin Description
PIN NAME
FUNCTION
1
FSET
Set Charge-Pump Frequency Input. FSET = GND selects 330kHz and FSET = IN selects 1MHz. Do not leave
FSET unconnected.
2
SHDN
Shutdown Input. The device shuts down, the output disconnects from the input, and the supply current
decreases to 1µA when SHDN is a logic low. Connect SHDN to IN for normal operation.
3
IN
Supply Input. Connect to an input supply in the 1.8V to 3.6V range. Bypass IN to GND with a (COUT / 2)µF
capacitor.
4
GND Ground. Analog ground for internal reference and control circuitry.
5
PGND Power Ground. Charge-pump current flows through this pin.
6
C1-
Negative Terminal of the Charge-Pump Capacitor
7
C1+
Positive Terminal of the Charge-Pump Capacitor
8
OUT 3.3V Power Output. Bypass OUT to GND with an output filter capacitor (see the Design Procedure section).
_______________Detailed Description
The MAX679 regulated charge pump has a 50% duty-
cycle clock. In phase one (charge phase), the charge-
transfer capacitor (C1) charges to the input voltage,
and output current is delivered by the output filter
capacitor (COUT). In phase two (transfer phase), C1 is
placed in series with the input and connects to the out-
put, transferring its charge to COUT. If the clock were to
run continuously, this process would eventually gener-
ate an output voltage equal to two times the input volt-
age (hence the name “doubler”).
The charge pump regulates by gating the oscillator on
and off as needed to maintain output regulation. This
method has low quiescent current, but to achieve
acceptable output ripple, C1 must be significantly
lower in value than COUT.
Start-Up Sequence
The MAX679 soft-start circuitry prevents excessive cur-
rent from being drawn from the battery at start-up or
when the output is shorted. This is done by limiting the
charge pump to 1/10 the normal current until either the
output is in regulation or the first 4096 charge-pump
4 _______________________________________________________________________________________
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