MP8869SGL datasheet(21/39 Pages) MPS

21 / 39 page

MP8869S

– 18V, 12A, SYNCHRONOUS, STEP-DOWN CONVERTER

MP8869S Rev. 1.03

www.MonolithicPower.com

1/18/2018

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

PG implements an adjustable deglitch time via

the I2C whenever VOUT crosses the under-

voltage and over-voltage (UV, OV) rising and

falling threshold. This guarantees the correct

indication when the output voltage is scaled

through the I2C.

The PG output is pulled low immediately when

UVLO,

input

UVLO,

OCP,

over-

temperature protection (OTP) are triggered.

Input Over-Voltage Protection (VIN OVP)

The MP8869S monitors VIN to detect an input

over-voltage event. This function is active only

when the output is in OV or a soft-stop

condition. When the output is in the over-

voltage protection (OVP) state or soft stop is

enabled, output discharge is enabled to charge

the input voltage high. When the input voltage

exceeds the input OVP threshold, both the HS-

FET and LS-FET stop switching.

Output Over-Voltage Protection (OVP)

The MP8869S monitors both FB and VOUT to

detect an over-voltage event. When the FB

voltage becomes higher than 125% of the

internal

reference

voltage,

internal

comparator monitors FB, and the controller

enters dynamic regulation mode. The input

voltage may be charged up during this time.

When input OVP is triggered, the IC stops

switching. If OVP mode is set to auto retry in

the I2C, the IC begins switching once the input

voltage drops below the VIN OVP recover

threshold. Otherwise, the MP8869S latches off.

OVP auto-retry mode or latch-off mode occurs

only if the soft start has finished.

Dynamic regulation mode can be operated by

turning on the low side until the low-side

negative current limit is triggered. Then the

body diode of the HS-FET free-wheels the

current.

The output power charges the input, which may

trigger the VIN OVP function. In VIN OVP,

neither the HS-FET or LS-FET turn on and stop

charging VIN. If the output is still over-voltage

and the input voltage drops below the VIN OVP

threshold, repeat the operation. If the output

voltage is below 110% of the internal reference

voltage, then output OVP is exited.

Output Absolute Over-Voltage Protection

(OVP_ABS)

he MP8869S’s VOUT can be adjusted by the

feedback reference voltage and the external

resistor dividers. But MP8869S’s output voltage

must be set lower than the absolute OVP

threshold (typically 6.5V).

The

MP8869S

monitors

VOUT

detect

absolute OVP. When VOUT is larger than 6.5V,

the controller enters dynamic regulation mode if

the OVP retry bit is set to 1 in the I2C register

01. Otherwise, the MP8869S latches off when

output OVP and input OVP are both triggered.

Absolute OVP works once both the input

voltage and EN are higher than their rising

thresholds. This means that this function can

work even during a soft start.

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the silicon die reaches temperatures that

exceed 160°C, the entire chip shuts down.

When the temperature is less than its lower

threshold (typically 140°C), the chip is enabled

again.

The D[1] and D[2] bits can be monitored in

silicon temperature.

Floating Driver and Bootstrap Charging

An external bootstrap capacitor powers the

floating power MOSFET driver. This floating

driver has its own UVLO protection. This

UVLO’s rising threshold is 2.4V with a 150mV

hysteresis. The bootstrap capacitor voltage is

regulated by VIN internally through D1, M1, C4,

L1, and C2 (see Figure 6). If VBST - VSW exceeds

3.3V, U1 regulates M1 to maintain a 3.3V BST

voltage across C4.

VIN

3.3V

BST

VOUT

Figure 6: Internal Bootstrap Charging Circuit

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