MAX682ESA Maxim Integrated Products, MAX682ESA Datasheet - Page 6
MAX682ESA
Manufacturer Part Number
MAX682ESA
Description
Charge Pumps 3.3VIn to Reg 5Vout Charge Pump
Manufacturer
Maxim Integrated Products
Datasheet
1.MAX682ESA.pdf
(12 pages)
Specifications of MAX682ESA
Function
Step Up
Output Voltage
5.05 V
Output Current
250 mA
Maximum Operating Temperature
+ 85 C
Package / Case
SOIC-8 Narrow
Minimum Operating Temperature
- 40 C
Mounting Style
SMD/SMT
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3.3V-Input to Regulated 5V-Output
Charge Pumps
The MAX682/MAX683/MAX684 charge pumps provide
a regulated 5V output from a 2.7V to 5.5V input. They
deliver a maximum of 250mA, 100mA, or 50mA load
current, respectively. Designed specifically for com-
pact applications, a complete regulator circuit requires
only three small external capacitors and one resistor.
An externally adjustable switching frequency and inno-
vative control scheme allow the circuit to be optimized
for efficiency, size, or output noise. The devices also
contain a shutdown feature.
The MAX682/MAX683/MAX684 consist of an error
amplifier, a 1.23V bandgap reference, an internal resis-
tive feedback network, an oscillator, high-current MOS-
FET switches, and shutdown and control logic (Figure
1). Figure 2 shows an idealized unregulated charge-
pump voltage doubler. The oscillator runs at a 50%
duty cycle. During one half of the period, the transfer
capacitor (C
other half, the doubler stacks the voltage across C
and the input voltage, and transfers the sum of the two
voltages to the output filter capacitor (C
than simply doubling the input voltage, the
MAX682/MAX683/MAX684 provide a regulated fixed
output voltage (5V) using either skip mode or constant-
frequency mode. Skip mode and constant-frequency
mode are externally selected via the SKIP input pin.
Figure 1. Functional Block Diagram
6
_______________________________________________________________________________________
SHDN
SKIP
IN
X
) charges to the input voltage. During the
SHDN
Detailed Description
CONTROL
LOGIC
OSC
EN
1.23V
SWITCHES
PGND
OUT
). Rather
OUT
CXP
CXN
X
In skip mode (SKIP = low), the error amplifier disables
switching when it detects an output higher than 5V. The
device then skips switching cycles until the output volt-
age drops. Then the error amplifier reactivates the
oscillator. Figure 3 illustrates the regulation scheme.
This regulation method minimizes operating current
because the device does not switch continuously. SKIP
is a logic input and should not remain floating.
When SKIP is high, the charge pump runs continuously
at the selected frequency. Figure 4 shows a block dia-
gram of the device in constant-frequency mode. The
error amplifier controls the charge on C
gate of the N-channel FET. When the output voltage
falls, the gate drive increases, resulting in a larger volt-
age across C
put ripple. Since the device switches continuously, the
Figure 2. Unregulated Voltage Doubler
Figure 3. Skip-Mode Regulation
C
IN
IN
IN
C
IN
S1
S1
X
. This regulation scheme minimizes out-
C
X
Constant-Frequency Mode
S2
OSCILLATOR
C
X
EN
OSC
S2
X
by driving the
Skip Mode
C
OUT
OUT
OUT