Data Sheet

LT83203/LT83205

analog.com

Rev. B

36 of 44

(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

1

49.9

49.9

1.2

69.8

49.9

1.8

130

49.9

3.3

280

49.9

5

453

49.9

Shorted and Reversed Input Protection

The LT83203/LT83205 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

LT83203/LT83205 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 LT83203/LT83205’s output. If the VIN pin is allowed to float and

the EN/UVLO pin is held high, then the LT83203/LT83205’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 ~50μA.

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

the LT83203/LT83205 can pull current from the output through the SW pin and the VIN pin.

Figure 57 shows a connection of the VIN and EN/UVLO pins, which allows the LT83203/LT83205 to run only when the

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

Figure 57. Reverse VIN Protection

VIN

VIN

D1

LT83203/

LT83205

EN/UVLO

GND