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MP1495DJ-LF-P

P1-P3P4-P6P7-P9P10-P12P13-P15
MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER
MP1495 Rev. 1.05 www.MonolithicPower.com 10
4/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
This protection mode is especially useful when
the output is dead-shorted to ground. The
average short-circuit current is greatly reduced
to alleviate the thermal issue and to protect the
regulator. The MP1495 exits the hiccup mode
once the over-current condition is removed.
Thermal Shutdown
Thermal shutdown prevents the chip from
operating at exceedingly high temperatures.
When the silicon die temperature exceeds
150°C, it shuts down the whole chip. When the
temperature drops below its lower threshold
(typically 130°C) the chip is enabled again.
Floating Driver and Bootstrap Charging
An external bootstrap capacitor powers the
floating power MOSFET driver. This floating
driver has its own UVLO protection, with a
rising threshold of 2.2V and hysteresis of
150mV. The bootstrap capacitor voltage is
regulated internally by V
IN
through D1, M1, C4,
L1 and C2 (Figure 3). If (V
IN
-V
SW
) exceeds 5V,
U1 regulates M1 to maintain a 5V BST voltage
across C4.
A 10 resistor placed between SW and
BST cap is strongly recommended to reduce SW
spike voltage.
Figure 3: Internal Bootstrap Charging Circuit,
Startup and Shutdown
If both V
IN
and EN exceed their appropriate
thresholds, the chip starts: The reference block
starts first, generating stable reference voltage
and currents, and then the internal regulator is
enabled. The regulator provides stable supply
for the remaining circuitries.
Three events can shut down the chip: EN low,
V
IN
low, and thermal shutdown. In the shutdown
procedure, the signaling path is first blocked to
avoid any fault triggering. The COMP voltage
and the internal supply rail are then pulled down.
The floating driver is not subject to this
shutdown command.
MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER
MP1495 Rev. 1.05 www.MonolithicPower.com 11
4/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
APPLICATION INFORMATION
Setting the Output Voltage
The external resistor divider sets the output
voltage. The feedback resistor R1 also sets the
feedback loop bandwidth with the internal
compensation capacitor (see Typical Application
on page 1). Choose R1 around 40k, then R2 is:
OUT
R1
R2
V
1
0.807V
=
−
Use the T-type network when V
OUT
is low, as
shown in Figure 4.
FB
8
RT
R2
R1
VOUT
Figure 4: T-Type Network
Table 1 lists the recommended T-type resistor
value for common output voltages.
Table 1: Resistor Selection for Common Output
Voltages
V
OUT
(V) R1 (kΩ) R2 (kΩ) Rt (kΩ)
1.0 20.5(1%) 82(1%) 82(1%)
1.2 30.1(1%) 60.4(1%) 82(1%)
1.8 40.2(1%) 32.4(1%) 56(1%)
2.5 40.2(1%) 19.1(1%) 33(1%)
3.3 40.2(1%) 13(1%) 33(1%)
5 40.2(1%) 7.68(1%) 33(1%)
Selecting the Inductor
For most applications, use a 1µH-to-10µH
inductor with a DC current rating that is at least
25% percent higher than the maximum load
current. Select an inductor with a DC resistance
less than 15m for highest efficiency. For most
designs, the inductance value can be derived
from the following equation.
OUT IN OUT
1
IN L OSC
V(VV)
L
VIf
×−
=
×Δ ×
Where I
L
is the inductor ripple current.
Choose an inductor ripple current to be
approximately 30% of the maximum load current.
The maximum inductor peak current is:
2
I
II
L
LOAD)MAX(L
Δ
+=
Use a larger inductor for light-load conditions
(below 100mA) for improved efficiency.
Setting the AAM Voltage
The AAM voltage sets the transition point from
AAM to CCM. Select a voltage that balances
efficiency, stability, ripple, and transient: A
relatively low AAM voltage improves stability and
ripple, but degrades transient and efficiency
during AAM mode; a relatively high AAM voltage
improves the transient and efficiency during AAM,
but degrades stability and ripple.
AAM voltage is set from the tap of a resistor
divider from the V
CC
(5V) pin, as shown in Figure
5.
R3
AAM
VCC(5V)
R4
Figure 5: AAM Network
Generally, choose R4 to be around 10k, then
R3 is:
⎟
⎠
⎞
⎜
⎝
⎛
−= 1
AAM
VCC
R4R3
MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER
MP1495 Rev. 1.05 www.MonolithicPower.com 12
4/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
AAM(V)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
024681012
V
OUT
=1.05V
V
OUT
=1.8V
V
OUT
=2.5V
V
OUT
=5V
V
OUT
=3.3V
Figure 6: AAM Selection for Common Output
Voltages (V
IN
=4.5V to 16V)
Selecting the Input Capacitor
The input current to the step-down converter is
discontinuous and therefore requires a capacitor to
supply the AC current to the step-down converter
while maintaining the DC input voltage. Use low-ESR
capacitors for the best performance. For best results,
use ceramic capacitors with X5R or X7R
dielectrics because of their low ESR and small
temperature coefficients. Use a 22µF capacitor
for most applications.
C1 requires an adequate ripple current rating since it
absorbs the input switching current. Estimate the
RMS current in the input capacitor with:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
−×=
IN
OUT
IN
OUT
LOAD1C
V
V
1
V
V
II
The worst case condition occurs at V
IN
= 2V
OUT
,
where:
2
I
I
LOAD
1C
=
For simplification, choose an input capacitor
whose RMS current rating greater than half of the
maximum load current.
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, place a small, high-quality ceramic
capacitor (e.g. 0.1F) as close to the IC as
possible. When using ceramic capacitors, make
sure that they have enough capacitance to
provide sufficient charge to prevent excessive
voltage ripple at the input. The input voltage
ripple caused by capacitance can be estimated
by:
LOAD OUT OUT
IN
IN
SIN
IV V
V1
fC1V V
⎛⎞
Δ= × ×−
⎜⎟
×
⎝⎠
Selecting the Output Capacitor
The output capacitor (C2) maintains the DC
output voltage. Use ceramic, tantalum, or low-
ESR electrolytic capacitors. For best results, use
low-ESR capacitors to keep the output voltage
ripple low. The output voltage ripple can be
estimated by:
OUT OUT
OUT ESR
S1 IN S
VV
1
V1R
fL V 8fC2
⎛⎞
⎛⎞
Δ= ×− × +
⎜⎟
⎜⎟
×××
⎝⎠
⎝⎠
Where L
1
is the inductor value and R
ESR
is the
equivalent series resistance (ESR) value of the
output capacitor.
For ceramic capacitors, the capacitance
dominates the impedance at the switching
frequency, and thus causes the majority of the
output voltage ripple. For simplification, the
output voltage ripple can be estimated by:
OUT OUT
OUT
2
IN
S1
VV
V1
V
8f L C2
⎛⎞
=×−
⎜⎟
×××
⎝⎠
For tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching
frequency. For simplification, the output ripple
can be approximated to:
OUT OUT
OUT ESR
IN
S1
VV
V1R
fL V
⎛⎞
=×−×
⎜⎟
×
⎝⎠
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP1495 can be optimized for a wide range of
capacitance and ESR values.
P1-P3P4-P6P7-P9P10-P12P13-P15

MP1495DJ-LF-P

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Buy MP1495DJ-LF-P
Manufacturer:
Monolithic Power Systems (MPS)
Description:
Switching Voltage Regulators 2A 16V 500kHz Sync Step-Down Converter
Lifecycle:
New from this manufacturer.
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