MP8869 datasheet(20/37 Pages) MPS

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MP8869

– 17V, 12A, SYNCHRONOUS STEP-DOWN CONVERTER

PRELIMINARY SPECIFICATIONS SUBJECT TO CHANGE

MP8869 Rev.1.0

www.MonolithicPower.com

6/8/2016

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

PG implements an adjustable deglitch time via

the I

2C whenever VOUT crosses the UV/OV

rising and falling threshold. This guarantees the

correct indication when the output voltage is

scaled through the I

2C.

The PG output is pulled low immediately when

either EN UVLO, input UVLO, OCP, or OTP are

triggered.

Input Over-Voltage Protection (VIN OVP)

The MP8869 monitors VIN to detect an input

over-voltage event. This function is active only

when the output is in OV or soft-stop condition.

When the output is in 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 MP8869 monitors both FB and VOUT to

detect an over-voltage event. When setting the

V_BOOT bit to 1, an internal comparator

monitors FB. When setting the V_BOOT bit to 0,

the internal comparator monitors VOUT. When

the FB or VOUT voltage becomes higher than

125% of the internal reference voltage, the

controller enters dynamic regulation mode, and

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 I

2C, the IC begins switching once the input

voltage drops below the VIN OVP recover

threshold. Otherwise, the MP8869 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)

The MP8869 monitors the VOUT voltage to

detect absolute over-voltage protection. When

VOUT is larger than 6.5V, the controller enters

dynamic regulation mode if the OVP retry bit is

set to 1 in the I

2C register 01. Otherwise, the

MP8869 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 5). If VBST - VSW exceeds

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

voltage across C4.

VIN

3.3V

BST

VOUT

Figure 5: Internal Bootstrap Charging Circuit

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