MAX77505

16V Input, 4.6A Switching Current Low IQ Buck

Converter

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Analog Devices | 13

Output Voltage Selection with RSEL

Whenever the MAX77505 is enabled, it reads the resistance (RSEL) between the SEL and AGND and programs the output

voltage according to Table 1. Ensure that RSEL resistors have 1% or better tolerances.

Table 1. RSEL Selection Table

RSEL (Ω)

VOUT (V)

RSEL (Ω)

VOUT (V)

≤ 95.3

3.3

3.74k

3.0

200

0.8

8.06k

3.2

309

0.9

12.4k

3.4

422

1.0

16.9k

3.6

536

1.1

21.5k

3.7

649

1.2

26.1k

3.8

768

1.3

30.9k

4.0

909

1.5

36.5k

4.2

1.05k

1.8

42.2k

4.3

1.21k

1.9

48.7k

4.5

1.40k

2.2

56.2k

5.0

1.62k

2.3

64.9k

5.2

1.87k

2.5

75.0k

5.3

2.15k

2.7

86.6k

5.5

2.49k

2.8

100k

3.1

2.87k

2.9

≥ 115k

4.8

Switch Current Limit

The MAX77505 provides a cycle-by-cycle switch current limit (ILIM) at the high-side MOSFET. When the peak current

limit is triggered, the MAX77505 turns off the high-side MOSFET immediately and the low-side MOSFET starts to

discharge the inductor current and the high-side MOSFET stays off until the inductor current reaches 50% of the ILIM. In

case the MAX77505 detects peak current limit events more than 16 times consecutively, the MAX77505 enters hiccup

mode and keeps both high-side and low-side MOSFETs off for about 15ms before attempting startup again.

When the zero crossing is detected at the low-side MOSFET, both the high-side and the low-side MOSFETs are turned

off (Hi-Z state of LX node) until the voltage at the OUTS pin falls below its target output voltage.

Output Voltage Active Discharge

When the MAX77505 is disabled by the EN pin or the UVLO fault event, the active discharge circuit is engaged to

discharge the energy stored at the output capacitor. When the active discharge circuit is activated, a 120Ω (typ) resistor

is connected between the OUTS pin and AGND.

Undervoltage Lockout

When the input voltage falls below the UVLO falling threshold (VUVLO_F, 2.375V, typ) during the operation, the MAX77505

disables the buck output immediately. If the EN pin is kept high, the MAX77505 automatically reinitiates the startup

procedure when the input voltage rises above the UVLO rising threshold (VUVLO_R, 2.450V typ).

Thermal Shutdown

When the junction temperature exceeds 150⁰C (typ), the buck converter output is latched off and is not allowed to restart

until the junction temperature drops below the thermal shutdown hysteresis level (130⁰C, typ). Once the junction

temperature cools down, either power cycling of the input voltage or toggling the EN pin is required to restart the buck

converter from the latch-off state.