LM46002PWPR datasheet(22/52 Pages) TI

22 / 52 page

LM46002

SNVSA13B – APRIL 2014 – REVISED SEPTEMBER 2014

www.ti.com

Feature Description (continued)

8.3.10 Bootstrap Voltage (BOOT)

The driver of the HS switch requires a bias voltage higher than VIN when the HS switch is ON. The capacitor

connected between CBOOT and SW pins works as a charge pump to boost voltage on the CBOOT pin to (VSW +

VCC). The boot diode is integrated on the LM46002 die to minimize the Bill-Of-Material (BOM). A synchronous

switch is also integrated in parallel with the boot diode to reduce voltage drop on CBOOT. A high quality ceramic

0.47 µF 6.3 V or higher capacitor is recommended for CBOOT.

8.3.11 Power Good (PGOOD)

The LM46002 has a built in power-good flag shown on PGOOD pin to indicate whether the output voltage is

within its regulation level. The PGOOD signal can be used for start-up sequencing of multiple rails or fault

protection. The PGOOD pin is an open-drain output that requires a pull-up resistor to an appropriate DC voltage.

Voltage seen by the PGOOD pin should never exceed 12 V. A resistor divider pair can be used to divide the

voltage down from a higher potential. A typical range of pull-up resistor value is 10 k

Ω to 100 kΩ.

When the FB voltage is within the power-good band, +4% above and -7% below the internal reference VREF

typically, the PGOOD switch will be turned off and the PGOOD voltage will be pulled up to the voltage level

defined by the pull up resistor or divider. When the FB voltage is outside of the tolerance band, +10 % above or -

13 % below VREF typically, the PGOOD switch will be turned on and the PGOOD pin voltage will be pulled low to

indicate power bad. Both rising and falling edges of the power-good flag have a built-in 220 µs (typical) deglitch

delay.

8.3.12 Over Current and Short Circuit Protection

The LM46002 is protected from over-current conditions by cycle-by-cycle current limiting on both peak and valley

of the inductor current. Hiccup mode will be activated if a fault condition persists to prevent over heating.

High-side MOSFET over-current 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. Please refer

to Functional Block Diagram for more details. The peak current of the HS switch is limited by the maximum EA

output voltage minus the slope compensation at every switching cycle. The slope compensation magnitude at the

peak current is proportional to the duty cycle.

When the LS switch is turned on, the current going through it is also sensed and monitored. The LS switch will

not be turned OFF at the end of a switching cycle if its current is above the LS current limit ILS-LIMIT. The LS

switch will be kept ON so that inductor current keeps ramping down, until the inductor current ramps below ILS-

LIMIT. Then the LS switch will be turned OFF and the HS switch will be turned on after a dead time. If the current

of the LS switch is higher than the LS current limit for 32 consecutive cycles and the power-good flag is low,

hiccup current protection mode will be activated. In hiccup mode, the regulator will be shutdown and kept off for

5.5 ms typically before the LM46002 tries to start again. If over-current or short-circuit fault condition still exist,

hiccup will repeat until the fault condition is removed. Hiccup mode reduces power dissipation under severe over-

current conditions, prevents over heating and potential damage to the device.

Hiccup is only activated when power-good flag is low. Under non-severe over-current conditions when VOUT has

not fallen outside of the PGOOD tolerance band, the LM46002 will reduce the switching frequency and keep the

inductor current valley clamped at the LS current limit level. This operation mode allows slight over current

operation during load transients without tripping hiccup. If the power-good flag becomes low, hiccup operation

will start after LS current limit is tripped 32 consecutive cycles.

8.3.13 Thermal Shutdown

Thermal shutdown is a built-in self protection to limit junction temperature and prevent damages due to over

heating. Thermal shutdown turns off the device when the junction temperature exceeds 160°C typically to

prevent further power dissipation and temperature rise. Junction temperature will reduce after thermal shutdown.

The LM46002 will attempt to restart when the junction temperature drops to 150°C.

Submit Documentation Feedback

Product Folder Links: LM46002

LM46002PWPR Datasheet(PDF) 22 Page - Texas Instruments

LM46002PWPR Datasheet(HTML) 22 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

Datasheet Download

Link URL