uP1537

5

uP1537-DS-F0000, Feb. 2018

www.upi-semi.com

Functional Description

POK

The uP1537 has POK output that indicates high when

switcher output is within the target. The POK function is

activated after soft-start has finished. If the output voltage

becomes within 90% of the target value, internal

comparators detect POK state and the POK signal

becomes high after a 1ms internal delay. If the output

voltage goes outside of 55% of the target value, the POK

signal becomes low. The POK output is an open-drain

output and should be pulled up externally if used.

Output Discharge Control

When EN is low, the uP1537 discharges the output

capacitor using internal MOSFET connected between

PHASE and GND while high side and low side MOSFETs

are kept off. The current capability of this MOSFET is

limited to discharge slowly.

Over Current Limit

The uP1537 monitors the inductor valley current by low

side MOSFET R

limit is triggered once the sensing current level is higher

than V

high side MOSFET off even the voltage loop commands

it to turn on.

The output voltage will decrease if the load continuously

demands more current than current limit level. The current

limit level is set at I

90% of its target level, letting V

UVP occurs and shuts down the uP1537.

The current limit threshold is set by connecting a resistor

from CS to GND. The CS pin will sink a 10µA current

source and create a voltage drop across R

V

low side MOSFET equals the voltage across the setting

resistor, the current limit will be activated.

The voltage across PHASE and GND pins is compared

with V

calculated as:

2

I

R

8

V

I

RIPPLE

)

ON

(

DS

OCSET

LIM

+

×

=

where I

steady state.

Over Voltage/Under Voltage Protection

The uP1537 monitors feedback voltage to detect

overvoltage and undervoltage. When the feedback voltage

becomes higher than 125% of the target voltage, the OVP

is triggered, high side MOSFET is off and low side

MOSFET is on. When the feedback voltage is lower than

55% of the target voltage, the UVP is triggered, then high

side MOSFET and low side MOSFET are latched. This

function is enabled after 1ms following EN has becomes

high.

VCC5 UVLO

The uP1537 has VCC5 under voltage lockout protection

(UVLO) that inhibits switching and resets the protection

faults.

When the VCC5 voltage is lower than UVLO threshold

voltage, all functions are turned off. This is the non-latch

protection.

Over Temperature Protection

The uP1537 monitors the temperature of itself. If the

turned off. This is the non-latch protection. It will be