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MAX1822ESA

High-Side Power Supply

Maxim Integrated 

High-Side Power Supply

4-CHANNEL LOAD SWITCH—NO PULLUP RESISTORS

+3.5V TO +16.5V

C4

1µF

C1

0.01µF

C2

0.01µF

1

C1+

C3 10µF

8

5

VCC VOUT

7 C1-

6

C2+

MAX1822

2

C2-

GND

4

NOTE 1: TRANSISTOR TYPE DEPENDS

ON LOAD-CURRENT REQUIREMENTS.

SW1

NOTE 2: 1µF CAPACITORS SUPRESS SWITCHING

SW2

TRANSIENTS—VALUE DEPENDS

ON LOAD CURRENT.

SW3

SW4

16

V+

2

N01

9

N02

12

N03

19

N04

4

NC1

7 NC2

14

NC3

17

NC4

5 V-

IN1

1

COM1 3

8

COM2

MAX333

13

COM3

COM4 18

IN2 IN3 IN4

10 11 20

ALL TRANSISTORS = IRF541 (NOTE 1)

TO LOAD

TO LOAD

TO LOAD

TO LOAD

ALL CAPACITORS = 1µF (NOTE 2)

Figure 5. MAX1822 Powering a MAX333 Quad Analog Switch, Realizing a 4-Channel Load Switch with No Pullup Resistors

4-Channel Load Switch with

No Pullup Resistors

Multiple high-side switches can be driven from a single

MAX1822 high-side power supply with no pullup resis-

tors on the FET gates. In Figure 5, a MAX1822 supplies

high-side voltage to a MAX333 quad analog switch to

control any one of four high-side switches. The FET

gates are normally connected to ground when the

MAX333 logic inputs are low.

Low-Dropout Regulator

In Figure 6, a MAX1822 high-side power supply powers

an LM10 reference and op-amp combination, providing

sufficient gate drive to turn on the FET. This allows the

regulator to achieve less than 70mV dropout at 1A load

using an IRF541, and just under 20mV for a

SMP60N06.

The 200mV reference section is configured for a gain of

25 (e.g., 200mV x 25 = 5V) and connects to the nonin-

verting input of the op amp; the regulator’s output con-

nects directly to the inverting input. The op amp

amplifies the error between its inputs and varies the

gate drive to the FET, regulating the output. Capacitor

C6 reduces transients due to load changes; its size

depends on the magnitude of the load change in the

application and can be reduced or eliminated if the

load remains relatively constant. With C6 = 1000µF, the

output transient to a 1A load pulsed at 20Hz is typically

less than 150mV. The regulator is turned on by apply-

ing VBATT to the Enable/Shutdown input and turned off

by pulling this input to ground.

The regulator output voltage, VOUT, is set by the ratio of

R1 to R2, calculated as follows:

R2

=

R1





VOUT

0.2

− 1

If the application does not require logic shutdown, con-

nect the MAX1822 VCC pin directly to the battery and

eliminate D2.

8 _______________________________________________________________________________________

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