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MPQ9842 Datasheet(PDF) 26 Page - MPS Industries, Inc.

Part # MPQ9842
Description  36V, 2A, Low IQ,Step-Down Converter AEC-Q100 Qualified
PDF  37 Pages
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Manufacturer  MPSIND [MPS Industries, Inc.]
Direct Link  http://www.mpsind.com/index.html
Logo MPSIND - MPS Industries, Inc.

MPQ9842 Datasheet(HTML) 26 Page - MPS Industries, Inc.

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MPQ9842
– 36V, 2A, LOW IQ, SYNCHRONOUS STEP-DOWN CONVERTER
MPQ9842 Rev. 1.1
www.MonolithicPower.com
26
7/29/2022
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2022 MPS. All Rights Reserved.
ensure that they have enough capacitance to
provide a sufficient charge to prevent excessive
voltage ripple at the input.
The input voltage ripple caused by capacitance
can be estimated with Equation (8):
=
 −
LOAD
OUT
OUT
IN
SW
IN
IN
IN
I
V
V
V
(1
)
f
C
V
V
(8)
Selecting the Output Capacitor
The output capacitor maintains the DC output
voltage.
Ceramic,
tantalum,
or
low
ESR
electrolytic capacitors are recommended. For
best results, use low ESR capacitors to keep
the output voltage ripple low. The output
voltage ripple can be estimated with Equation
(9):
=
 −
+

OUT
OUT
OUT
ESR
SW
IN
SW
OUT
VV
1
V
(1
) (R
)
f
L
V
8f
C
(9)
Where L is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
For
ceramic
capacitors,
the
capacitance
dominates the impedance at the switching
frequency and causes the majority of the output
voltage ripple. For simplification, the output
voltage ripple can be estimated with Equation
(10):
=
 −
 
OUT
OUT
OUT
2
SW
OUT
IN
VV
V
(1
)
8 f
L C
V
(10)
For tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching
frequency. For simplification, the output ripple
can be approximated with Equation (11):
=
 −
OUT
OUT
OUT
ESR
SW
IN
VV
V
(1
) R
f
L
V
(11)
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MPQ9842 can be optimized for a wide range of
capacitance and ESR values.
VIN UVLO Setting
The MPQ9842 has an internal, fixed, UVLO
threshold. The rising threshold is 2.8V, while
the
falling threshold is
about 2.65V. For
applications that need a higher UVLO point, the
external resistor divider between VIN and EN
can be used to achieve a higher equivalent
UVLO threshold (see Figure 5).
Figure 5: Adjustable UVLO Using EN Divider
The UVLO threshold can be calculated with
Equation (12) and Equation (13):
EN_RISING
DOWN
UP
RISING
V
R
R
(1
INUV
+
=
)
(12)
EN_FALLING
DOWN
UP
FALLING
V
R
R
(1
INUV
+
=
)
(13)
Where VEN_RISING is 1.05V, and VEN_FALLING is
0.93V.
External BST Diode and Resistor
An external BST diode can enhance the
efficiency of the regulator when the duty cycle is
high. A power supply between 2.5V and 5V can
be used to power the external bootstrap diode.
VCC or VOUT is recommended to be this power
supply in the circuit (see Figure 6).
CBST
COUT
L
BST
SW
External BST diode
IN4148
VCC / VOUT
VCC
VOUT
RBST
Figure 6: Optional External Bootstrap Diode to
Enhance Efficiency
The recommended external BST diode is
IN4148, and the recommended BST capacitor
value is 0.1µF to 1μF.
A resistor in series with BST capacitor (RBST)
can reduce the SW rising rate and voltage
spikes. This helps enhance EMI performance
and reduce voltage stress at a high VIN. A
higher
resistance is better for SW spike
reduction but compromises efficiency. To make
VIN
EN
VIN
RUP
RDOWN



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