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MP1494DJ-LF-Z

P1-P3P4-P6P7-P9P10-P12P13-P15
MP1494 – SYNCHRONOUS STEP-DOWN CONVERTER
MP1494 Rev. 1.04 www.MonolithicPower.com 10
12/26/2012 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
circuit current is greatly reduced to alleviate
thermal issues and to protect the regulator. The
MP1494 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 reaches temperatures that
exceed 150°C, it shuts down the whole chip.
When the temperature is less than 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. This
UVLO’s rising threshold is 2.2V with a
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 will regulate 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.
V
IN
V
OUT
D1
M1
BST
C4
R4
L1
SW
U1
5V
C2
Figure 3: Internal Bootstrap Charging Circuit,
Startup and Shutdown
If both V
IN
and EN exceed their respective
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 a 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.
MP1494 – SYNCHRONOUS STEP-DOWN CONVERTER
MP1494 Rev. 1.04 www.MonolithicPower.com 11
12/26/2012 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
APPLICATION INFORMATION
Setting the Output Voltage
The external resistor divider sets the output
voltage (see Typical Application on page 1). 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. R2 is then given by:
OUT
R1
R2
V
1
0.807V
=
−
The T-type network—as shown in Figure 4—is
highly recommended when V
OUT
is low.
FB
8
RT
R2
R1
VOUT
Figure 4: T-Type Network
Table 1 lists the recommended T-type resistors
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
Use a1µH-to-10µH inductor with a DC current
rating of at least 25% percent higher than the
maximum load current for most applications. For
highest efficiency, use an inductor with a DC
resistance less than 15m. 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 the 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 improved efficiency
under light-load conditions—below 100mA.
Setting the AAM Voltage
The AAM voltage sets the transition point from
AAM to CCM. Select a voltage to balance
efficiency, stability, ripple, and transient.
A low AAM voltage improves stability and ripple,
but degrades transient and efficiency during AAM.
Likewise, a high AAM voltage improves the
transient and efficiency during AAM, but
degrades stability and ripple.
The AAM voltage comes from the tap of a
resistor divider from V
CC
(5V) to GND, 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
MP1494 – SYNCHRONOUS STEP-DOWN CONVERTER
MP1494 Rev. 1.04 www.MonolithicPower.com 12
12/26/2012 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 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 Values for Common Output
Voltages (V
IN
= 4.5V to 16V)
Selecting the Input Capacitor
The input current to the step-down converter is
discontinuous, therefore requires a capacitor is to
supply the AC current to the step-down converter
while maintaining the DC input voltage. Use low ESR
capacitors for the best performance. Use ceramic
capacitors with X5R or X7R dielectrics for best
results because of their low ESR and small
temperature coefficients. For most applications,
use a 22µF capacitor.
Since C1 absorbs the input switching current, it
requires an adequate ripple current rating. The RMS
current in the input capacitor can be estimated by:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
−×=
IN
OUT
IN
OUT
LOAD1C
V
V
1
V
V
II
The worse case condition occurs at V
IN
= 2V
OUT
,
where:
2
I
I
LOAD
1C
=
For simplification, choose an input capacitor with
an 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, add a small, high quality ceramic
capacitor (e.g. 0.1F) placed 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 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 the capacitance 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
MP1494 can be optimized for a wide range of
capacitance and ESR values.
P1-P3P4-P6P7-P9P10-P12P13-P15

MP1494DJ-LF-Z

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