LM25069PMMX-2SLASHNOPB datasheet(13/29 Pages) TI1

13 / 29 page

RS =

50 mV

ILIM

Shutdown

Control

VIN

UVLO/EN

OVLO

GND

LM25069

VSYS

LM25069

www.ti.com

SNVS607E – FEBRUARY 2011 – REVISED MARCH 2013

Shutdown Control

The load current can be remotely switched off by taking the UVLO pin below its threshold with an open collector

or open drain device, as shown in Figure 26. Upon releasing the UVLO pin the LM25069 switches on the load

current with in-rush current and power limiting.

Figure 26. Shutdown Control

Power Good Pin

The Power Good indicator pin (PGD) is connected to the drain of an internal N-channel MOSFET capable of

sustaining 17V in the off-state, and transients up to 20V. An external pull-up resistor is required at PGD to an

appropriate voltage to indicate the status to downstream circuitry. The off-state voltage at the PGD pin can be

higher or lower than the voltages at VIN and OUT. PGD is switched high when the voltage from SENSE to OUT

(the external MOSFET’s VDS) decreases below 1.3V. PGD switches low when the MOSFET’s VDS is increased

past 1.9V. If the UVLO pin is taken below its threshold or the OVLO pin taken above its threshold, to disable the

LM25069, PGD switches low within 10 µs without waiting for the voltage at OUT to fall. The PGD output pin is

high when the voltage at VIN is less than 1.6V.

Application Information (Refer to Figure 21)

CURRENT LIMIT, RS

The LM25069 monitors the current in the external MOSFET (Q1) by measuring the voltage across the sense

resistor (RS), connected from VIN to SENSE. The required resistor value is calculated from:

where

•

ILIM is the desired current limit threshold

(1)

If the voltage across RS reaches 50 mV, the current limit circuit modulates the gate of Q1 to regulate the current

at ILIM. While the current limiting circuit is active, the fault timer is active as described in the Fault Timer & Restart

section. For proper operation, RS must be no larger than 200 mΩ.

While the maximum load current in normal operation can be used to determine the required power rating for

resistor RS, basing it on the current limit value provides a more reliable design since the circuit can operate near

the current limit threshold continuously. The resistor’s surge capability must also be considered since the circuit

breaker threshold is approximately twice the current limit threshold. Connections from RS to the LM25069 should

be made using Kelvin techniques. In the suggested layout of Figure 27 the small pads at the lower corners of the

sense resistor connect only to the sense resistor terminals, and not to the traces carrying the high current. With

this technique, only the voltage across the sense resistor is applied to VIN and SENSE, eliminating the voltage

drop across the high current solder connections.

Submit Documentation Feedback

Product Folder Links: LM25069

LM25069PMMX-2/NOPB bảng dữ liệu(PDF) 13 Page - Texas Instruments

LM25069PMMX-2/NOPB bảng dữ liệu(HTML) 13 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

bảng dữ liệu tải về

Link URL