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MPQ8634B Datasheet(HTML) 16 Page - Monolithic Power Systems

Part No. MPQ8634B
Description  16V, 20A, Sync, Step-Down Converter with Adjustable Current Limit, Programmable Frequency, and Voltage Tracking
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Maker  MPS [Monolithic Power Systems]
Homepage  http://www.monolithicpower.com
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MPQ8634B Datasheet(HTML) 16 Page - Monolithic Power Systems

 
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MPQ8634B – 16V, 20A, SYNC, STEP-DOWN CONVERTER W/ ADJUSTABLE CURRENT LIMIT,
PROGRAMMBALE FREQUENCY, AND VOLTAGE TRACKING
MPQ8634B Rev. 1.02
www.MonolithicPower.com
16
11/16/2018
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2018 MPS. All Rights Reserved.
If VFB exceeds 116% of VREF, the device enters
latch-off OVP mode. The HS-FET latches off
and PGOOD latches low until the power of VCC
or EN is recycled. Meanwhile, the LS-FET
remains on until it reaches the low-side
negative current limit (NOCP). Once it hits
NOCP, the LS-FET is momentarily turned off for
200ns and is then turned on again. The
MPQ8634B maintains this operation to bring
down the output voltage. When VFB drops below
50% of VREF, the LS-FET is turned off for pulse-
skip mode and keeps turning on for forced CCM
operation. If VFB rises back to more than 116%
of VREF, the LS-FET turns on again with NOCP
until VFB drops back below 50% of VREF. The
power of EN or VIN must be recycled to clear
the OVP fault.
The OVP function is enabled after TRK/REF
reaches 900mV.
Over-Temperature Protection (OTP)
The MPQ8634B has an over-temperature
protection (OTP). The IC monitors the junction
temperature
internally.
If
the
junction
temperature exceeds the threshold value
(typically 160°C ), the converter shuts off. This
is a latch-off protection. Enable the part by
recycling the power of VCC or EN.
The OTP function is effective once the
MPQ8634B is enabled.
Output Voltage Setting and Remote Output
Voltage Sensing
First choose a value for R1. Then R2 can be
determined with Equation (5):
REF
21
OREF
V
R (k)
R (k)
VV

(5)
Where VREF is 900mV.
To optimize the load transient response, a feed-
forward capacitor (CFF) is recommended in
parallel with R1. R1 and CFF add an extra zero
to the system, which improves loop response.
R1 and CFF are selected so that the zero
formed by R1 and CFF is located around
20kHz ~ 60kHz. See Equation (6):
Z
FF
1
f
2R1 C

(6)
Power Good (PGOOD)
The MPQ8634B has a power good (PGOOD)
output. PGOOD is the open-drain of a MOSFET.
Connect PGOOD to VCC or another external
voltage source (less than 3.6V) through a pull-
up resistor (typically 10kΩ). After applying the
input voltage, the MOSFET turns on, so
PGOOD is pulled to GND before TRK/REF is
ready. After VFB reaches 92.5% of VREF,
PGOOD is pulled high after 0.8ms of delay.
When VFB drops to 80% of VREF or exceeds
116% of the nominal VREF, PGOOD is latched
low. PGOOD can only be pulled high again
after a new soft start.
If the input supply fails to power the MPQ8634B,
PGOOD is clamped low, even though PGOOD
is tied to an external DC source through a pull-
up resistor. The relationship between the
PGOOD voltage and the pull-up current is
shown in Figure 5.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0.60.7
0.80.9
V_PG(V)
Figure 5: PGOOD Clamped Voltage vs. Pull-Up
Current
Enable (EN) Configuration
The MPQ8634B turns on when EN goes high.
The MPQ8634B turns off when EN goes low.
EN cannot be left floating for proper operation.
EN can be driven by an analog or digital control
logic signal to enable or disable the MPQ8634B.


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