IN

OUT

OUT

OUT _ MAX

LS _ LIMIT

SW

IN

V

V

V

I

I

2 f

L

V

u

u

u

Z _ESR

OUT

1

f

2

C

ESR

S u

u

16

LMR23625-Q1

SNVSAR5B – DECEMBER 2016 – REVISED MARCH 2018

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Copyright © 2016–2018, Texas Instruments Incorporated

Feature Description (continued)

(8)

on the tolerance of the chosen component. This may reduce its impedance and ease noise coupling on the FB

8.3.8 Bootstrap Voltage (BOOT)

The LMR23625-Q1 provides an integrated bootstrap voltage regulator. A small capacitor between the BOOT and

SW pins provides the gate-drive voltage for the high-side MOSFET. The BOOT capacitor is refreshed when the

high-side MOSFET is off and the low-side switch conducts. The recommended value of the BOOT capacitor is

0.1 μF. TI recommends a ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 16V or

higher for stable performance over temperature and voltage.

8.3.9 Overcurrent and Short-Circuit Protection

The LMR23625-Q1 is protected from overcurrent conditions by cycle-by-cycle current limit on both the peak and

valley of the inductor current. Hiccup mode is activated if a fault condition persists to prevent overheating.

High-side MOSFET overcurrent protection is implemented by the nature of the peak-current-mode control. The

HS switch current is sensed when the HS is turned on after a set blanking time. The HS switch current is

compared to the output of the error amplifier (EA) minus slope compensation every switching cycle. See the

Functional Block Diagram for more details. The peak current of HS switch is limited by a clamped maximum-

by the slope compensation and remains constant over the full duty-cycle range.

The current going through LS MOSFET is also sensed and monitored. When the LS switch turns on, the inductor

current begins to ramp down. The LS switch is not turned OFF at the end of a switching cycle if its current is

switch is turned on after a dead time. This is somewhat different than the more typical peak-current limit and

results in Equation 9 for the maximum load current.

(9)

If the current of the LS switch is higher than the LS current limit for 64 consecutive cycles, hiccup current

protection mode is activated. In hiccup mode the regulator is shut down and kept off for 5 ms typically before the

LMR23625-Q1 tries to start again. If overcurrent or short-circuit fault condition still exists, hiccup repeats until the

fault condition is removed. Hiccup mode reduces power dissipation under severe overcurrent conditions,

prevents overheating and potential damage to the device.

turned off until the next clock cycle. This is used to protect the LS switch from excessive negative current.

8.3.10 Thermal Shutdown

The LMR23625-Q1 provides an internal thermal shutdown to protect the device when the junction temperature

exceeds 170°C (typical). The device is turned off when thermal shutdown activates. Once the die temperature

falls below 155°C (typical), the device reinitiates the power-up sequence controlled by the internal soft-start

circuitry.