Rainbow Electronics MAX8719 - Manual (Page 7)

MAX8718/MAX8719
High-Voltage, Low-Power Linear Regulators for
Notebook Computers
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Detailed Description
The MAX8718/MAX8719 low-quiescent-current linear
regulators are designed primarily for high-input-voltage
applications. The MAX8718 supplies a preselected
3.3V or 5.0V output for loads up to 100mA (Figure 1).
The MAX8719 provides an adjustable voltage from
1.24V to 28V (Figure 2). The maximum output current is
a function of the package’s maximum power dissipation
for a given temperature. A 5µA load is required to main-
tain output regulation.
The MAX8718’s output voltage is fed back through an
internal resistive voltage-divider connected to OUT. Set
the output voltage to either 5.0V or 3.3V with the 5/3
pin. Select the 5V output by connecting 5/3 to OUT, or
the 3.3V output by connecting 5/3 to GND.
The MAX8719’s output is adjustable with an external
resistive voltage-divider. The typical feedback thresh-
old is 1.24V (see the
Setting the MAX8719 Output
Voltage section). See Figure 3 for the MAX8718/
MAX8719 Functional Diagram.
Shutdown
The device enters shutdown mode when SHDN is low.
In shutdown mode, the internal pnp power transistor,
control circuit, reference, and all biases turn off, reduc-
ing the supply current to below 3µA. Connect SHDN to
IN for automatic startup.
Pin Description
PIN
MAX8718 MAX8719
NAME FUNCTION
1 1 IN Positive Supply Input. Connect to a +4V to +28V supply.
2 2 GND Ground
3 — 5/3 P r eset Outp ut- V ol tag e S el ect Inp ut. C onnect 5/3 to GN D for 3.3V outp ut, or to OU T for 5V outp ut.
— 3 FB Feedback Input. Regulates to 1.24V nominally.
4 4 V CC PGOOD Sense Input
5 5 PGOOD Power-Good Output
6 6 SHDN Shutdown Control Input
7 7 I.C.
Internal Connection. This pin is internally connected for test purposes; leave it unconnected
in the application.
8 8 OUT 100mA Regulator Output
MAX8718
GND
I.C.
6V TO
28V
1 µF
IN
SHDN
OUT
V
CC
PGOOD
5/3
100k Ω
10 µF
OUTPUT
3.3V
PGOOD
MAX8719
GND
I.C.
6V TO
28V
1 µF
IN
SHDN
OUT
V CC
PGOOD
FB
100k Ω
10 µF
OUTPUT
PGOOD
R1
R2
Figure 1. Typical Operating Circuit of the MAX8718 Figure 2. Typical Operating Circuit of the MAX8719