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MAX1822ESA
High-Side Power Supply
_______________General DescriptionThe MAX1822 high-side supply, using a regulated
charge pump, generates a regulated output voltage
11V greater than the input supply voltage to power
high-side switching and control circuits. The MAX1822
allows low-resistance N-channel MOSFETs (FETs) to be
used in circuits that normally require costly, less effi-
cient P-channel FETs and PNP transistors. The high-
side output also eliminates the need for logic FETs in
+5V and other low-voltage switching circuits.
A +3.5V to +16.5V input supply range and a typical qui-
escent current of only 150µA make the MAX1822 ideal
for a wide range of line- and battery-powered switching
and control applications where efficiency is crucial.
Also provided is a logic-level power-ready output (PR)
to indicate when the high-side voltage reaches the
proper level.
The MAX1822 comes in an 8-pin SO package and
requires three inexpensive external capacitors. The
MAX1822 is a pin-for-pin replacement to the MAX622.
________________________ApplicationsHigh-Side Power Control with N-Channel FETs
Low-Dropout Voltage Regulators
Power Switching from Low Supply Voltages
H-Switches
Stepper Motor Drivers
Battery-Load Management
Portable Computers
____________________________Features+3.5V to +16.5V Operating Supply Voltage RangeOutput Voltage Regulated to VCC+ 11V (typ)150µA (typ) Quiescent CurrentPower-Ready Output
MAX1822
High-Side Power Supply
Pin Configuration
Typical Operating Circuit19-1892; Rev 0; 1/01
MAX1822
High-Side Power Supply
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICSStresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 1:High-side voltage measured with respect to ground.
Note 2:For VCC> +13V on the MAX1822, use C1 = C2 = 0.01µF.
Note 3:Power-Ready Threshold is the voltage with respect to ground at VOUTwhen PR switches high (PR = VCC).
VCC......................................................................................+17V
VOUT....................................................................................+30V
IOUT...................……………………………………………….25mA
Continuous Total Power Dissipation (TA= +70°C)
8-pin SO (derate 5.88mW/°C above +70°C)...............471mW
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10s).................................+300°C
MAX1822
High-Side Power SupplyMAX1822
SUPPLY CURRENT
vs. C3 CAPACITOR VALUE
MAX1822 toc01
C3 CAPACITOR VALUE (µF)
SUPPLY CURRENT (
MAX1822 toc02
C3 CAPACITOR VALUE (µF)
SUPPLY CURRENT (
MAX1822
SUPPLY CURRENT
vs. C3 CAPACITOR VALUEMAX1822 toc03
VCC (V)
SUPPLY CURRENT (mA)
MAX1822
SUPPLY CURRENT
vs. SUPPLY VOLTAGE0.81.00.40.60.21.21.41.61.82.0
MAX1822 toc05
IOUT (mA)
OUT
(V)
MAX1822
OUTPUT VOLTAGE
vs. OUTPUT CURRENTMAX1822 toc04
C1 = C2 CAPACITANCE VALUE (µF)
MAXIMUM I
OUT
MAX1822
MAXIMUM OUTPUT CURRENT
vs. C1 = C2 CAPACITOR VALUE NOTE:
CURRENT AT THE POINT
WHERE VOUT BEGINS TO
LOSE REGULATION.3125678910
MAX1822 toc05
IOUT (mA)
OUT
(V)
MAX1822
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
__________________________________________Typical Operating Characteristics
MAX1822
High-Side Power Supply
Typical Operating Characteristics (continued)
MAX1822
High-Side Power Supply
Detailed Description
Charge-Pump OperationThe MAX1822 is a multistage charge-pump power sup-
ply. Although the charge pump is capable of multiply-
ing VCCup to four times, the output is regulated to VCC
+ 11V by an internal feedback circuit for inputs above
4V. The charge pump typically operates at 90kHz, but
regulates by pulse skipping. When VOUTexceeds VCC
+ 11V, the oscillator shuts off. As VOUTdips below VCC
+ 11V, the oscillator turns on.
Power-Ready OutputThe Power-Ready Output (PR) signals control circuitry
when the high-side voltage reaches a preset level. This
feature can be used to protect external FET switches
from excess dissipation and damage by preventing them
from turning on, except when adequate gate drive levels
are present. When power is applied, PR remains low until
VOUTreaches approximately VCC+ 8.5V. PR also goes
low if VOUTfalls below this level during operation, i.e., if
the output is overloaded. The PR high level is VCC.
Applications Information
Quiescent Supply CurrentMAX1822 quiescent supply current varies with VCCand
with the values of C1, C2, and C3 (Typical Operating
Characteristics). Even with no external load, the device
must still pump to overcome internal losses. Large ratios
between C3 and C1 or C2 require more charge-pump
cycles to restore VOUT. As VCCfalls below 5V, quiescent
current rises fairly rapidly to about 1mA at 4V (Typical
Operating Characteristics). This rise occurs because
VOUTno longer pulse skips to regulate at low input volt-
ages; the oscillator runs continuously, so supply current
is higher. Figure 2shows the test circuit for the
MAX1822 quiescent supply current.
MAX1822
Output RippleVOUTripple is typically 50mVp-p with VCC= +5V, C1
and C2 = 0.047µF, and C3 = 1µF (Typical Operating
Characteristics). Ripple can be reduced by increasing
the ratio between the output storage capacitors C3 and
C1 and C2. This is usually accomplished by increasing
C3 and keeping C1 and C2 in the 0.01µF to 0.047µF
range. For example, if C1 and C2 are 0.047µF (VCC
must not exceed 13V) and C3 is 10µF, output ripple
typically falls to 15mV (TypicalOperatingCharacter-
istics).
Capacitor SelectionCapacitor type is unimportant when selecting capaci-
tors for the MAX1822. However, when VCCexceeds
13V, C1 and C2 must be no greater than 0.01µF. Using
larger value capacitors with input voltages above 13V
causes excessive amounts of energy to pass through
High-Side Power Supply