LT3045 datasheet(36/45 Pages) AD

36 / 45 page

Data Sheet

LT83201

analog.com

Rev. A 36 of 45

(IPGFB) from the Electrical Characteristics table must be considered when determining the resistor divider network.

Note that the programmable power good and fast start-up capabilities are disabled when PGFB is tied to 0.5V or

when the device is in shutdown.

The PGFB pin current (IPGFB) can be ignored if RPGFB(BOT) is less than 50kΩ. Table 8 suggests some 1% PGFB resistor

divider values for common VOUT configurations.

Table 8. Suggested PGFB Resistor Divider Values

VOUT (V)

RPGFB(TOP) (kΩ)

RPGFB(BOT) (kΩ)

0.8

29.4

48.7

0.9

39.2

48.7

49.9

1.2

69.8

49.9

1.8

130

49.9

3.3

280

49.9

453

49.9

Shorted and Reversed Input Protection

The LT83201 tolerates a shorted output. The bottom switch current is monitored such that if the inductor current is

beyond safe levels, switching on of the top switch is delayed until the inductor current falls to safe levels.

There is another situation to consider in systems where the output is held high when the input to the LT83201 is

absent. This occurs in battery charging applications or in battery backup systems where a battery or some other

supply is diode ORed with the LT83201’s output. If the VIN pin is allowed to float and the EN/UVLO pin is held high,

then the LT83201’s internal circuitry pulls its quiescent current through its SW pin. This is acceptable if the system

can tolerate current draw in this state. If the EN/UVLO pin is grounded, the SW pin current drops to ~40µA.

However, if the VIN pin is grounded while the output is held high, regardless of EN/UVLO, parasitic body diodes inside

the LT83201 can pull current from the output through the SW pin and the VIN pin.

Figure 59 shows a connection of the VIN and EN/UVLO pins, which allows the LT83201 to run only when the input

voltage is present and protects against a shorted or reversed input.

Figure 59. Reverse VIN Protection

VIN

LT83201

EN/UVLO

GND

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