LTC4365 データシートの表示（PDF） - Linear Technology

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LTC4365

UV and OV and Reverse Supply Protection Controller

Linear Technology 

LTC4365

APPLICATIONS INFORMATION

Figure 4 shows the timing associated with the UV pin.

Once a UV fault propagates through the UV comparator

(tFAULT), the FAULT output is asserted low and a 50mA

current sink discharges the GATE pin. As VOUT falls, the

GATE pin tracks VOUT.

UV

VUV

VUV + VUVHYST

FAULT

GATE

tFAULT

tFAULT

tGATE(FAST)

tRECOVERY

EXTERNAL N-CHANNEL MOSFET

TURNS OFF

4365 F04

Figure 4. UV Timing (OV < (VOV – VOVHYST), SHDN > 1.2V)

Figure 5 shows the timing associated with the OV pin.

Once an OV fault propagates through the OV comparator

(tFAULT), the FAULT output is asserted low and a 50mA

current sink discharges the GATE pin. As VOUT falls, the

GATE pin tracks VOUT.

OV

VOV

VOV – VOVHYST

tFAULT

tFAULT

FAULT

GATE

tGATE(FAST)

tRECOVERY

EXTERNAL N-CHANNEL MOSFET

TURNS OFF

4365 F05

Figure 5. OV Timing (UV > (VUV + VUVHYST), SHDN > 1.2V)

When both the UV and OV faults are removed, the external

MOSFET is not immediately turned on. The input supply

must remain within the user selected power good window

for at least 36ms (tRECOVERY) before the load is again

connected to the supply. This recovery timeout period

filters noise (including line noise) at the input supply and

prevents chattering of power at the load.

Procedure for Selecting UV/OV External Resistor Values

The following 3-step procedure helps select the resistor

values for the resistive divider of Figure 3. This procedure

minimizes UV and OV offset errors caused by leakage

currents at the respective pins.

1. Choose maximum tolerable offset at the UV pin,

VOS(UV). Divide by the worst case leakage current at

the UV pin, IUV (10nA). Set the sum of R1 + R2 equal

to VOS(UV) divided by 10nA. Note that due to the

presence of R3, the actual offset at UV will be slightly

lower:

R1+ R2 = VOS(UV)

IUV

2. Select the desired VIN UV trip threshold, UVTH. Find

the value of R3:

( ) R3 = 2 •

VOS(UV )

IUV

•

UVTH – 0.5V

3. Select the desired VIN OV trip threshold, OVTH. Find

the values of R1 and R2:

VOS(UV) +R3

R1= IUV

2 • OVTH

R2 = VOS(UV) – R1

IUV

The example of Figure 3 uses standard 1% resistor values.

The following parameters were selected:

VOS(UV) = 3mV

IUV = 10nA

UVTH = 3.5V

OVTH = 18V

4365f

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