ISL9237EVAL2Z datasheet(33/40 Pages) RENESAS

33 / 40 page

ISL9237

FN8723 Rev.5.00

Page 33 of 40

Nov 29, 2017

Adapter Overvoltage Protection

If the ADP pin voltage exceeds 23.4V for more than 10µs, the

ISL9237 will consider an adapter overvoltage condition has

occurred. It will turn off the ASGATE MOSFETs to isolate the

adapter from the system, deassert the ACOK signal by pulling it

low and stop switching. BGATE will turn on for the battery to

support the system load. Once ADP voltage drops below 23.04V

from more than 100µs, it will start to turn on ASGATE and start

switching.

System Overvoltage Protection

The ISL9237 provides system rail overvoltage protection. If the

system voltage VSYS is 600mV higher than MaxSystemVoltage

switching. It will resume switching without the 1.3s or 150ms

debounce once VSYS drops 300mV below the system

overvoltage threshold.

Way Overcurrent Protection (WOCP)

In the case that the system bus is shorted, either a MOSFET short

or an inductor short, the input current could be high. ISL9237

includes input overcurrent protection to turn off the ASGATE and

stop switching.

The ISL9237 provides adapter current and battery discharging

current WOCP (Way Overcurrent Protection) function against the

MOSFET short, system bus short and inductor short scenarios.

ISL9237 monitors the CSIP-CSIN voltage and CSON-CSOP

voltage, compares them with the WOCP threshold 12A for

adapter current and 16A for battery discharge current.

When the WOC comparator is tripped, ISL9237 counts one time

within each 20µs. Whenever ISL9237 counts WOC to 7 times in

656ms, it turns off ASGATE, deasserts ACOK and stops switching

immediately. After the 1.3s or 150ms debounce time set by

Control2 register Bit<11>, it goes through the start-up sequence

to retry.

The WOCP function can be disabled through Control2 register

Bit<1>.

Over-Temperature Protection

The ISL9237 turns off the internal LDO for self protection when

the junction temperature exceeds +140°C. The internal LDO

stays off until the junction temperature falls below +120°C.

The ISL9237 stops switching after declaring over-temperature

protection.

Once the temperature falls below +120°C, and after a 100µs

delay, the ISL9237 will enable the internal LDO and the ISL9237

will resume operation.

Switching Power MOSFET Gate Capacitance

The ISL9237 includes an internal 5V LDO output at VDD pin,

which can be used to provide the switching MOSFET gate driver

power through VDDP pin with an R-C filter. The 5V LDO output

overcurrent protection threshold is 70mA nominal. When

selecting the switching power MOSFET, the MOSFET gate

capacitance should be considered carefully to avoid overloading

the 5V LDO, specially in Buck-boost mode when four MOSFETs

switching at the same time. For one MOSFET, the gate drive

current can be estimated by Equation 2:

Where:

•Qg is the total gate charge, which can be found in the MOSFET

datasheet

•fSW is switching frequency

Adapter Input Filter

The adapter cable parasitic inductance and capacitance could

cause some voltage ringing or an overshoot spike at the adapter

connector node when the adapter is hot plugged in. This voltage

spike could damage the ASGATE MOSFET or the ISL9237 pins

connecting to the adapter connector node. One low cost solution

is to add an RC snubber circuit at the adapter connector node to

clamp the voltage spike as shown in Figure 34. A practical value

of the RC snubber is 2.2Ω to 2.2µF while the appropriate values

and power rating should be carefully characterized based on the

actual design. Meanwhile, it is not recommended to add a pure

capacitor at the adapter connector node, which can cause an

even bigger voltage spike due to the adapter cable or the adapter

current path parasitic inductance.

Idriver

Qg f



(EQ. 2)

FIGURE 34. ADAPTER INPUT RC SNUBBER CIRCUIT

IS L 9237

AC IN

AS G A T E

AD AP T E R

CO NN E C T O R

R i

C i

2.2

2.2µ F

R C SN UB BER

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