ISL85001 查看數據表（PDF） - Renesas Electronics

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ISL85001

1A Standard Buck PWM Regulator

Renesas Electronics 

ISL85001

voltage, VOUT, of the regulator; see Equation 2. The value for the

feedback resistor is typically between 1kΩ and 10kΩ.

R4 = V-----O-R---U-1---T-----0–---.--60---.V--6---V---

(EQ. 2)

If the output voltage desired is 0.6V, then RP is left unpopulated.

VOUT

R1

EA

R4

0.6V

REFERENCE

FIGURE 21. EXTERNAL RESISTOR DIVIDER

The buck output can be programmed as high as 19V. Proper

heatsinking must be provided to insure that the junction

temperature does not exceed +125°C.

When the output is set greater than 2.7V, it is recommended to

preload at least 10mA and make sure that the input rise time is

much faster than the VOUT1 rise time. This allows the BOOT

capacitor adequate time to charge for proper operation.

Protection Features

The ISL85001 limits current in the power devices to limit on-chip

power dissipation. Overcurrent limits on the regulator protect the

internal power device from excessive thermal damage.

Undervoltage protection circuitry on the buck regulator provides

a second layer of protection for the internal power device under

high current condition.

Buck Regulator Overcurrent Protection

During the PWM on-time, the current through the internal

switching MOSFET is sampled and scaled through an internal

pilot device. The sampled current is compared to a nominal 1.7A

overcurrent limit. If the sampled current exceeds the overcurrent

limit reference level, an internal overcurrent fault counter is set

to 1 and an internal flag is set. The internal power MOSFET is

immediately turned off and will not be turned on again until the

next switching cycle.

The protection circuitry continues to monitor the current and

turns off the internal MOSFET as described. If the overcurrent

condition persists for eight sequential clock cycles, the

overcurrent fault counter overflows, indicating an overcurrent

fault condition exists. The regulator is shut down and power-good

goes low. If the overcurrent condition clears prior to the counter

reaching four consecutive cycles, the internal flag and counter

are reset.

The protection circuitry attempts to recover from the overcurrent

condition after waiting 4 soft-start cycles. The internal

overcurrent flag and counter are reset. A normal soft-start cycle

is attempted and normal operation continues if the fault

condition has cleared. If the overcurrent fault counter overflows

during soft-start, the converter shuts down and this hiccup mode

operation repeats.

There is 100ns blanking time for noise immunity. It is

recommended to operate the duty cycle higher than the blanking

time to insure proper overcurrent protection.

Undervoltage Protection

If the voltage detected on the buck regulator FB pin falls 25%

below the internal reference voltage, the undervoltage fault

condition flag is set. The regulator is shut down. The controller

enters a recovery mode similar to the overcurrent hiccup mode.

No action is taken for 4 soft-start cycles and the internal

undervoltage counter and fault condition flag are reset. A normal

soft-start cycle is attempted and normal operation continues if

the fault condition has cleared. If the undervoltage counter

overflows during soft-start, the converter is shut down and this

hiccup mode operation repeats.

Thermal Overload Protection

Thermal overload protection limits total power dissipation in the

ISL85001. There is a sensor on the chip to monitor the junction

temperature of the internal LDO and PWM switching power

N-channel MOSFET. When the junction temperature (TJ) of the

sensor exceeds +150°C, the thermal sensor sends a signal to the

fault monitor.

The fault monitor commands the buck regulator to shut down.

The buck regulator soft-starts turn on again after the IC’s junction

temperature cools by 20°C. The buck regulator experiences

hiccup mode operation during continuous thermal overload

conditions. For continuous operation, do not exceed the +125°C

junction temperature rating.

Application Guidelines

Operating Frequency

The ISL85001 operates at a fixed switching frequency of

500kHz.

Buck Regulator Output Capacitor Selection

An output capacitor is required to filter the inductor current and

supply the load transient current. The filtering requirements are a

function of the switching frequency and the ripple current. The

load transient requirements are a function of the slew rate (di/dt)

and the magnitude of the transient load current. These

requirements are generally met with a mix of capacitors and

careful layout.

Embedded processor systems are capable of producing transient

load rates above 1A/ns. High frequency capacitors initially supply

the transient and slow the current load rate seen by the bulk

capacitors. The bulk filter capacitor values are generally

determined by the ESR (Effective Series Resistance) and voltage

rating requirements rather than actual capacitance requirements.

FN6769 Rev.3.00

Apr 14, 2017

Page 11 of 16

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