LTC3589 datasheet(31/44 Pages) LINER

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LTC3589

3589p

If any enabled regulator output falls more than 8% low for

longer than 25μs PGOOD is pulled LOW and a status bit is

set in the PGSTAT register. The PGOOD pin and PGSTAT

status bit remain LOW for as long as the low voltage

condition persists plus 250μs.

An extended low output rail causing the PGOOD pin to

be LOW for longer than 14ms deﬁnes a PGOOD timeout

fault condition that triggers a hard reset if not masked in

I2C register bit SCR2[7].

During a dynamic voltage slew, PGOOD is pulled LOW

unless bit 5 in the dynamic target voltage register for each

regulator is set HIGH. When SCR2[7] is HIGH, PGOOD

remains in normal operation. The status register PGSTAT

is unaffected by a dynamic voltage slew.

Undervoltage Detection

The LTC3589 under voltage (UV) detection circuit will

output a fault condition, locking out regulator operation,

until VIN reaches 2.7V (typical). Once VIN is above the

fault threshold the LTC3589 will operate normally until VIN

drops to 2.6V (typical). When VIN drops below 2.6V, the

OPERATION

Figure 14 shows the PGOOD pin and PGSTAT status reg-

ister timing. When no regulator is enabled, the PGOOD

pin is pulled LOW and PGSTAT bits are LOW. PGOOD and

the PGSTAT bits are HIGH 250μs after the last enabled

regulator is within 7% of its target.

Figure 14. PGOOD Pin and PGSTAT Status Register Timing

VOUTx

PGOOD

IRQ

3589 F14

ENx

200μs

25μs

1sec

14ms

250μs

ENABLE

DISABLE

UNDERVOLTAGE

DISABLED IF

WAKE LOW

WAKE HIGH AFTER 1sec

IF PWR_ON HIGH

EXTENDED

UNDERVOLTAGE

(FAULT)

WAKE

250μs

fault condition initiates a hard shutdown reset. Figure 15

shows undervoltage warning and fault detection levels.

Figure 15. UV Detection Hard Reset and Warning Levels

VIN

UNDERVOLTAGE

VIN

FAULT

WARNING

3589 F15

2.55V

2.65V

2.9V

An undervoltage warning sets register bit IRQSTAT[4] and

pulls the IRQ pin LOW.

To minimize standby quiescent current the UVLO and

thermal sensor circuits are disabled when all the regula-

tors are off.

Thermal Shutdown Fault and Warning

Similar to the VIN undervoltage detection circuits the over

temperature detection circuits check for warning and fault

levels. An over temperature fault will initiate a fault induced

shutdown. An over temperature warning sets register bit

IRQSTAT[6] and pulls the IRQ pin LOW.

IRQ Pin and IRQSTAT Status Register Function

The IRQ pin and IRQSTAT status register report PGOOD

timeout fault, VIN undervoltage warning and fault, and

high temperature warning and fault. Table 15 shows the

meaning of the IRQSTAT read only status register bits.

Table 15. IRQSTAT Read Only Register Bit Deﬁnitions

IRQSTAT[BIT]

VALUE

SETTING

PGOOD Timeout Fault (PGOOD low >

14ms)

VIN Under Voltage Warning (VIN < 2.9V)

VIN Under Voltage Fault (VIN < 2.6V)

Thermal Limit Warning (TJ > 130°C)

Thermal Limit Fault (TJ > 150°C)

LTC3589 Datasheet(PDF) 31 Page - Linear Technology

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