DATA SHEET
SKY87203: 3.5 A Constant On-Time, Step-Down DC-DC Converter
Applications
Description
Portable devices
The SKY87203 is a variable switching frequency, 3.5 A constant
on-time, synchronous step-down converter. The device provides
an output voltage from 0.9 V to 4.0 V from input voltage ranging
from 2.7 V to 6.0 V, while keeping excellent line and load
regulation and maximizing efficiency.
Access points
Set-top boxes
Input voltage range: 2.7 V to 6.0 V
The constant on-time control allows easy loop stabilization with
minimal external components while providing fast transient
response.
Output voltage range: 0.9 V to 4.0 V
Power sequencing is controlled by the EN and PG pins.
Variable switching frequency: 600 kHz to 1.5 MHz
The SKY87203 has cycle-by-cycle current limits and thermal
shutdown to protect against fault conditions.
Features
Up to 3.5 A continuous output current
95% peak efficiency
Typical switch on resistance: 50 m PMOS, 40 m NMOS
80% light load efficiency
Power sequencing
The SKY87203 is available in a 12-pin, 2 mm 2 mm Quad Flat
No-Lead (QFN) package. A typical application circuit is shown in
Figure 1. The pin configuration and packages are shown in
Figure 2. Signal pin assignments and functional pin descriptions
are provided in Table 1.
Cycle-by-cycle over-current protection
Auto-discharge at power-off
Over-temperature protection
Control loop stabilization with low ESR ceramic capacitors
Soft start
Low profile, QFN (12-pin, 2 mm 2 mm) package (MSL1,
260 C per JEDEC J-STD-020)
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
SKY87203
Input Voltage
2.7 V to 6 V
1
C1
22 μF
10
8
Power Good
9
VIN
OUT
FB
EN
PG
FSET
4
L1
2, 11
1 μH
6
C2
22 μF
Output Voltage
3.6 V
R1
294 kΩ
7
R2
57.6 kΩ
5
R3
300 kΩ
PGND
AGND
Enable
LX
PVIN
3, 12
t0282
VIN
Figure 1. Typical Application Circuit
PVIN 1
10
9
PG
8
EN
LX
LX 2
11
PGND
12
7
FB
AGND 4
5
6
OUT
FSET
PGND 3
S3203
Figure 2. SKY87203-11 Pinout – 12-Pin QFN Package
(Top View)
Table 1. SKY87203 Signal Descriptions
Pin
Name
Description
Pin
Name
Description
1
PVIN
Power supply.
7
FB
Feedback voltage pin. Used to control the converter
output voltage according to the ratio of the feedback
resistor.
2
LX
Switch node, connected to inductor.
8
EN
Enable pin, active high.
3
PGND
Power ground.
9
PG
Power good pin. Open drain with internal pull-up
resistor.
4
AGND
Analog ground.
10
VIN
Analog supply pin.
5
FSET
Switching frequency adjust pin. Connect with a resistor
to ground. If this pin is left floating, the switching
frequency is 1.2 MHz for an input voltage equal to 5 V
and an output voltage equal to 1.2 V.
11
LX
Switch node, connected to inductor.
6
OUT
Output voltage sensing pin.
12
PGND
Power ground.
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
Electrical and Mechanical Specifications
The absolute maximum ratings of the SKY87203 are provided in
Table 2. Recommended operating conditions are specified in
Table 3. Electrical specifications are provided in Table 4.
Table 2. SKY87203 Absolute Maximum Ratings (Note 1)
Parameter
Symbol
Minimum
Maximum
Units
VIN
0.3
+6.5
V
Switching voltage (LX to ground)
VLX
0.3
VIN + 0.3
V
Signal pins (FB, OUT, EN, PG to ground)
VFB, VOUT, VEN, VPG
0.3
+6.5
V
Maximum continuous current for load switch
IMAX
Junction temperature
TJ
Storage temperature
TSTG
Power pins (PVIN, VIN to ground)
65
3.5
A
+150
C
+150
C
Soldering temperature (at leads, 10 sec)
TLEAD
+260
C
Thermal resistance, junction-to-ambient
θJA
80
C/W
Thermal resistance, junction-to-case
θJC
16
C/W
Power dissipation @ 25 C
PD
1.6
W
Note 1: Exposure to maximum rating conditions for extended periods may reduce device reliability. There is no damage to device with only one parameter set at the limit and all other
parameters set at or below their nominal value. Exceeding any of the limits listed here may result in permanent damage to the device.
CAUTION: Although this device is designed to be as robust as possible, electrostatic discharge (ESD) can damage this device. This device
must be protected at all times from ESD. Static charges may easily produce potentials of several kilovolts on the human body
or equipment, which can discharge without detection. Industry-standard ESD precautions should be used at all times.
Table 3. SKY87203 Recommended Operating Conditions
Parameter
Symbol
Minimum
Typical
Maximum
Units
Input voltage range
VIN
2.7
6.0
V
Output voltage range
VOUT
0.9
4.0
V
Table 4. SKY87203 Electrical Specifications (1 of 2) (Note 1)
(VIN = 5.0 V, TA = –40 C to +85 C [Typical Values are TA = +25 C], Unless Otherwise Noted)
Parameter
Symbol
Test Condition
Min
Typical
Max
Units
Input shutdown current
ISHDN
VEN = 0 V
0
A
Quiescent supply current
IQ
VEN = 2 V, VFB = 0.63 V,
VIN = 3.6 V
40
A
Feedback voltage
VFB
2.7 V ≤ VIN ≤ 6.0 V
Feedback input bias current
IFB
VFB = 0.6 V
0.591
0.600
0.609
V
10
nA
High side switch on resistance (Note 2)
RDS(ON)_P
50
m
Low side switch on resistance (Note 2)
RDS(ON)_N
40
m
Switch leakage
VEN = 0 V, VIN = 6.0 V,
VLX = 0 V and 6.0 V
PFET current limit
3.6
Dampening resistor
RDAMP
0
2
A
4.5
6.0
A
200
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
Table 4. SKY87203 Electrical Specifications (2 of 2) (Note 1)
(VIN = 5.0 V, TA = –40 C to +85 C [Typical Values are TA = +25 C], Unless Otherwise Noted)
Parameter
On time
Symbol
tON
Test Condition
Min
Typical
Max
VIN = 5.0 V, VOUT = 1.2 V
RFSET = 600 k,
PWM Mode (0.6 MHz)
430
ns
VIN = 5.0 V, VOUT = 1.2 V
RFSET = 300 k,
PWM Mode (1.2 MHz)
220
ns
VIN = 3.6 V, VOUT = 1.2 V
RFSET = 300 k,
PWM Mode (1.2 MHz)
277
ns
VIN = 5.0 V, VOUT = 1.2 V
FSET = floating,
PWM Mode (1.2 MHz)
210
ns
VIN = 5.0 V, VOUT = 1.2 V
RFSET = 240 k,
PWM Mode (1.5 MHz)
170
ns
Minimum off time
tOFF
30
ns
Soft-start time
tSS_ON
1
ms
VIN discharge N-MOSFET switch on
resistance (Note 2)
RDSON_DSCHg
10
VIN discharge time
VIN_DSCHG
VIN (falling) = UVLO
UVLO VIN (falling) 1 V
90
PG pin upper trip threshold
VFB 0.66 V
+10
%
PG pin lower trip threshold
VFB 0.54 V
10
%
PG pin delay
200
ms
s
90
PG pin sink current capability
VPG_LO
0.4
PG pin logic high voltage
VPG_HI
PG pin internal pull-up resistor
RPG
500
k
Output voltage discharge resistor
RDSCHG
100
Under-Voltage Lock Out
UVLO
4.9
VIN rising
2.35
UVLO hysteresis
2.50
2.65
V
mV
0.4
VEN_L
VEN_H
V
V
400
EN pin input voltage:
Logic low
Logic high
1.2
V
V
2
0
A
A
Thermal shutdown
150
°C
Thermal hysteresis (Note 2)
30
°C
EN pin input current
VEN = 2 V
VEN = 0 V
Note 1: Performance is guaranteed only under the conditions listed in this table.
Note 2: Specification guaranteed by design.
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Units
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
Typical Performance Characteristics
Typical performance characteristics of the SKY87203 are
illustrated in Figures 3 through 21. The output voltage is 3.6 V.
80
60
85 ºC
25 ºC
40
–40 ºC
70
60
VIN = 4.2 V
50
VIN = 5.0 V
t0252
Quiescent Current (μA)
80
t0251
Quiescent Current (μA)
100
40
20
2.7
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.1
5.4
5.7
−40
6.0
−15
35
60
85
Temperature (ºC)
Supply Voltage (V)
Figure 3. Quiescent Current (Close Loop) vs Supply Voltage
Figure 4. Quiescent Current (Close Loop) vs Temperature
2
1.5
1.5
1
0.5
1
0.5
t0254
EN Off Threshold (V)
2
t0253
EN On Threshold (V)
10
0
0
−40
−15
10
35
60
−40
85
−15
35
60
85
Temperature (ºC)
Temperature (ºC)
Figure 6. EN Off Threshold vs Temperature
(VIN = 5 V, Load = 0 mA)
Figure 5. EN On Threshold vs Temperature
(VIN = 5 V, Load = 0 mA)
0.610
Feedback Voltage (V)
2
1.5
1
0.600
0.595
t0255
0.5
0.605
t0256
2.5
Frequency (MHz)
10
0.590
0
−40
−15
10
35
60
Temperature (ºC)
Figure 7. Frequency vs Temperature
(VIN = 5 V, Load = 500 mA)
85
−40
−15
10
35
60
85
Temperature (ºC)
Figure 8. Feedback Voltage vs Temperature
(VIN = 5 V, Load = 0 mA)
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70
70
65
65
NMOS RDS(ON) (mΩ)
PMOS RDS(ON) (mΩ)
DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
60
55
50
55
50
45
40
t0238
t0237
45
60
40
–40
–15
10
35
60
85
–40
–15
10
Temperature (ºC)
35
60
85
Temperature (ºC)
Figure 9. PMOS RDS(ON) vs Temperature
(VIN = 5 V)
Figure 10. NMOS RDS(ON) vs Temperature
(VIN = 5 V)
3.80
98
3.75
96
VOUT (V)
92
3.65
3.60
VIN = 4.2 V
VIN = 4.2 V
90
3.55
VIN = 5.0 V
VIN = 6.0 V
t0239
88
86
10
100
1000
3.50
VIN = 5.0 V
VIN = 6.0 V
t0240
Efficiency (%)
3.70
94
3.45
10
100
IOUT (mA)
IOUT (mA)
Figure 11. Efficiency vs IOUT
Figure 12. VOUT vs IOUT
VOUT (AC)
200 mV/div
ILOAD
1 A/div
0.7 A
t0241
0.2 A
t0242
VOUT (AC)
100 mV/div
ILOAD
1 A/div
1000
50 μs/div
Figure 13. Load Transient
(Load = 0.2 A to 2 A)
50 μs/div
Figure 14. Load Transient
(Load = 0.7 A to 3.5 A)
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
VOUT
2 V/div
0V
VEN
2 V/div
0V
PG
2 V/div
t0243
0V
200 μs/div
Figure 15. Power Good Delay
VOUT
2 V/div
VOUT
2 V/div
0V
VEN
2 V/div
VEN
2 V/div
0V
0A
ILX
2 A/div
VLX
5 V/div
0A
t0244
0V
VLX
5 V/div
0V
t0245
ILX
1 A/div
0V
0V
400 μs/div
1 ms/div
Figure 17. Shutdown Waveform
(Load = 2 A)
Figure 16. Shutdown Waveform
(Load = 0 A)
VEN
2 V/div
VEN
2 V/div
0V
0V
0A
ILX
1 A/div
0V
400 μs/div
Figure 18. Soft Start Waveform
(Load = 0 A)
VLX
5 V/div
0V
0A
t0247
VLX
5 V/div
VOUT
2 V/div
0V
t0246
VOUT
2 V/div
ILX
1 A/div
0V
400 μs/div
Figure 19. Soft Start Waveform
(Load = 2 A)
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
VOUT (AC)
50 mV/div
VOUT (AC)
50 mV/div
ILX (AC)
1 A/div
VLX
2 V/div
0V
1 μs/div
Figure 20. Typical Switching Waveform
(0 A Load)
VLX
2 V/div
t0249
0A
t0248
ILX
1 A/div
0V
1 μs/div
Figure 21. Typical Switching Waveform
(2 A Load)
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
VIN Auto Discharge
VIN
PVIN
+
EN
Voltage
References
and UVLO
–
VREF
COMP
+
FB
+
–
PWM
Control
and
Logic
Driver
Ramp
Circuit
LX
OUT
0.66 V
RDAMP
VOUT
Discharge
FSET
+
–
–
+
0.54 V
+
PGND
–
PG
t0283
Figure 22. SKY87203 Functional Block Diagram
Functional Description
The SKY87203 is an adaptive constant on-time, adjustable
voltage step-down DC-DC converter. A constant on-time control
architecture offers a simpler control loop and faster transient
response than a fixed-frequency Pulse Width Modulation (PWM)
control architecture.
The constant on-time converter maintains a constant output
frequency because the “on” time is inversely proportional to the
supply voltage. As the input voltage decreases, the “on” time is
increased, maintaining a relatively constant period.
The device is enabled using the EN input. When the EN pin is
pulled high, the converter starts up under the control of a 1 ms
soft start routine. Under light load conditions, the switch enters
pulse-skipping mode to ensure regulation is maintained. This
effectively changes the switching frequency.
To maintain a wide input voltage range, the switching period is
extended when either the minimum “off” or “on” time is reached.
The frequency is also affected when switching operates in
discontinuous mode. The “on” time of the switching pulses can
be estimated using the following equation:
t ON
VOUT
The minimum off time is fixed at 30 ns to prevent runaway
inductor current during load transients.
A functional block diagram of the SKY87203 is shown in
Figure 22.
Constant On-Time (COT) Operation
In normal continuous conduction mode, where the inductor
current (IL) never reaches zero, the high-side MOSFET is turned
on for a fixed interval (tON) determined by the COT sub-circuit (a
one-shot timer) within the PWM Control and Logic functional
block.
During that fixed interval, the inductor current starts to ramp up.
At the end of the tON period, the high-side MOSFET is turned off
and the low-side MOSFET is turned on causing the inductor
current to ramp down. Until this point, the voltage on the FB pin
(VFB) goes below the reference voltage (VREF) on the comparator,
which restarts the one-shot timer and initiates the next cycle.
The ideal tON time in continuous conduction mode is determined
by the following relationships:
Duty cycle (D) =
VOUT
V IN
0.833 s
V IN
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
On time (tON) = D
Light Load Operation
1
f SW
In discontinuous conduction mode, the SKY87203 uses a passive
damping scheme to reduce the amplitude and duration of ringing
that occurs at the switching node (LX).
If switching frequency (fSW) = 1.2 MHz, the on-time equation can
be rewritten as:
tON
VOUT
0.833 s
V IN
Enable and Soft Start
When the input voltage is greater than the Under-Voltage Lockout
(UVLO) threshold, the SKY87203 is enabled by pulling the EN pin
higher than 1.2 V. If the EN pin is left floating or pulled down to
ground, the regulator is disabled. There is an internal 1 M
resistor from the EN pin to ground.
The COT circuit generates an “on” time proportional to the ideal
duty cycle and holds the switching frequency constant. However,
due to nonlinearities in the COT circuit, propagation delays, and
non-ideal switch voltage drops due to output current loads, the
actual operating frequency can vary slightly.
When DC current loads are less than half of the peak-to-peak
current ripple in the inductor, the inductor current can drop to
zero or even become negative. When this happens, the SKY87203
operates in discontinuous conduction mode.
The SKY87203 step-down regulator soft-start control prevents
output voltage overshoot and limits inrush current when either the
input power or the enable input is applied. After the regulator is
enabled, the SKY87203 ramps up the internal target voltage with
a controlled slew rate of 1 ms.
During the “off” time, the low-side MOSFET is on and the
discontinuous conduction mode comparator monitors the current.
When the current is zero, the low-side MOSFET is turned off,
which prevents the current from going negative.
When the EN signal is pulled low, the regulator forces the
converter into a low-power, non-switching state, and forces the
switching node into a high-impedance shutdown state.
Both the high-side MOSFET and the low-side MOSFET remain off
with the output capacitor supplying the load current until the FB
pin voltage goes below the reference voltage, triggering a new
switching cycle. The switching frequency decreases in light load
conditions.
PG (Power Good) Pin
The SKY87203 has an open drain with a 500 k pull-up resistor
pin indicator (PG). When the FB pin is within ±10 percent of
regulation voltage, the PG pin is pulled up to VIN by the internal
resistor. If the FB pin voltage is not within ±10 percent of
regulation voltage, the PG pin is pulled down to ground by an
internal MOSFET. The MOSFET has a maximum RDS(ON) of less
than 100 .
Waveforms for both continuous conduction mode and
discontinuous conduction mode are shown in Figure 23.
VHSG
GND
VLSG
GND
IL
VSW
VOUT
tON
tOFF
VFB
GND
IOUT
ΔIL
VFB
tON
VFB(DC)
tOFF2
VHYS
VREF
tOFF1
Continuous
Discontinuous
Figure 23. Continuous and Discontinuous Mode Wave Forms
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
Current Limit and Short Circuit Protection
Table 5. Adjustable Resistor Values
The SKY87203 includes protection for overload condition and
short-circuit conditions by current-limiting the high-side
MOSFETs.
The SKY87203 enters over-load protection mode or short-circuit
protection mode when the inductor current hits the current limit
(4.5 A). The device will try to recover from the short circuit by
entering a “hiccup” mode, in which the regulator disables the
output power stage, discharges the soft-start capacitor, and
automatically tries a soft start again. If the overload or the shortcircuit condition still holds after a soft start ends, the SKY87203
repeats this protection operation cycle until the short circuit
disappears and the output rises back to the regulation level.
Flexible Switching Frequency Select Function
The SKY87203 has a flexible switching frequency select function
to satisfy the variable application requirement. If this pin is left
floating, the switching frequency is 1.2 MHz. A resistor (R3) is
connected between the FSET pin and ground to adjust the
switching frequency according to the following relationship:
Frequency = 1.2 MHz (300 k/R3)
Output Voltage
(V)
RFB2
(k 1%)
(RFB1 = 200 k 1%)
1.0
300
1.2
200
1.8
100
2.5
63.2
3.3
44.2
VIN Auto Discharge
The SKY87203 has a VIN auto-discharge function for USB
applications in which a large inrush current supplied by a large VIN
capacitor during a hot plugging operation exceeds the allowed
USB current limit. When VIN voltage falls below the UVLO
threshold, an N-MOSFET switch discharges the VIN to ground until
VIN is less than 1 V. The discharge time is typically 90 ms for the
condition UVLO VIN 1 V.
For example, a 500 F bulk input capacitor needs about 80 ms to
discharge an input voltage from 2.1 V to 1.0 V as illustrated in
Figure 25.
Application Information
RFB1
VOUT
0.6 V
1
As shown in Table 5, the values for both RFB1 and RFB2 are
rounded to the nearest 1 percent resistor value, and typically
selected to be between 10 k and 200 k. The lower resistance
value improves the noise immunity, but results in higher feedback
current (which reduces the efficiency).
VOUT
RFB1
FB
RFB2
Figure 24. Feedback Resistive Divider Circuit
VOUT
2 V/div
0V
ILX
20 mA/div
0 mA
t0250
The SKY87203 output voltage is adjustable from 0.9 V up to 4.0 V
by connecting the FB pin to the center tap of a resistor-divider
between the output and ground (see Figure 24). The resistive
feedback voltage divider sets the output voltage according to the
following relationship:
RFB 2
2.2 V
VIN
1 V/div
Setting the Output Voltage
20 ms/div
Figure 25. VIN Auto Discharge
Inductor Selection
Inductor values ranging from 0.82 H to 4.7 H are
recommended for most SKY87203 applications. Given the desired
input and output voltages, the inductor value and switching
frequency determine the ripple current:
V
V
I L OUT 1 OUT
VIN
f SW L
Lower ripple current reduces core losses in the inductor, Effective
Series Resistance (ESR) losses in the output capacitors, and
output voltage ripple. Highest efficiency operation is obtained at
low frequency with a small ripple current. However, achieving this
requires a large inductor. There is a trade-off between component
size, efficiency, and operating frequency.
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
to the capacitor’s ESL. Estimate the output voltage ripple due to
the output capacitance, ESR, and ESL as follows:
A reasonable starting point is to choose a ripple current that is
about 30 percent of the maximum output current, IOUT(MAX). The
largest ripple current occurs at the highest input voltage, Vin. To
guarantee that ripple current does not exceed a specified
maximum, the inductance should be chosen according to the
following relationship:
VOUT
L
f SW I L( MAX )
1 VOUT
VIN ( MAX )
VOUT ( RIPPLE ) VRIPPLE( C ) VRIPPLE( ESR ) VRIPPLE( ESL )
Where the output ripple due to output capacitance, ESR, and ESL
is:
V RIPPLE( C )
V RIPPLE( ESR ) I L ESR
The maximum inductor peak current is calculated according to:
I L( MAX ) I OUT
I L
8 C OUT f SW
I L( MAX )
VRIPPLE( ESL ) ( VIN VOUT )
2
ESL
ESL
VIN
L
L
The peak to peak inductor current, IL, is:
Manufacturer specifications list both the inductor DC current
rating, which is a thermal limitation, and the peak current rating,
which is determined by the saturation characteristics. The
inductor should not show any appreciable saturation under normal
load conditions.
I L
VIN
VOUT
VOUT
V IN
L f SW
The capacitive ripple and ESR ripple are phase shifted from each
other. Depending on the type of output capacitor chemistry, one
of them typically dominates. When ceramic capacitors are used
that generally have low ESR, VRIPPLE(C) dominates. When
electrolytic capacitors are used, VRIPPLE(ESR) dominates.
The saturation current is a very important parameter for inductor
selection. It must be more than the maximum peak current
through the inductor – an adequate margin is important for a safe
application.
Use ceramic capacitors for low ESR and low ESL at the switching
frequency of the converter. The ripple voltage due to ESL is
negligible when using ceramic capacitors.
Some inductors that meet the peak and average current rating
requirements still result in excessive losses due to a high Direct
Current Resistance (DCR). Always consider the losses associated
with DCR and their effect on the total regulator efficiency when
selecting an inductor.
After a load step occurs, the output capacitor must support the
difference between the load requirement and inductor current.
Once the average inductor current increases to the DC load level,
the output voltage recovers. Therefore, based on limitations in the
ability to discharge the inductor, a minimum output voltage
deviation may be determined by the following:
Recommended inductors are listed in Table 6.
Output Capacitor Selection
The output capacitor limits the output ripple and provides current
during large load transitions. A 22 F X5R or X7R ceramic
capacitor typically provides sufficient bulk capacitance to stabilize
the output during large load transitions and has the ESR and
Equivalent Series Inductance (ESL) characteristics necessary for
low output ripple.
V SOAR( C )
I 2 OUT L
2 C OUT VOUT
V SOAR( ESR ) I OUT ESR
Where VSOAR is the output voltage overshoot and undershoot
deviation.
The key parameters for selecting the output capacitors are
capacitance, ESR, ESL, and voltage ratings. Output ripple occurs
due to variations in the charge stored in the output capacitor, the
voltage drop due to the capacitor’s ESR, and the voltage drop due
Table 6. Recommended Inductor Selection
Manufacturer
Part Number
Inductance
(H)
Saturation Current
(A)
Temperature Current
(A)
Typical DCR
(m)
Size
W L H (mm)
Sumida
0520CDMCDS-1ROMC
1
8
5.9
17
5.75 5.45 2
Sumida
0420CDMCBDS-1R0MC
1
6.8
5.5
17
4.75 4.35 2
Wurth
74404063010
1
7.5
5.2
10
6 6 2.6
Toko
FDSD0515-H-1R0M
1
8.7
6.1
25
5.2 4.9 1.5
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
The ceramic output capacitor provides low ESR and low ESL,
which results in low output ripple dominated by capacitive ripple
voltage (VOUT(C)). However, due to the lower capacitance value,
the load transient response is significantly worse. Therefore,
ceramic output capacitors are generally recommended only for
designs with soft load transients (slow di/dt and/or small load
steps).
Tantalum and electrolytic capacitors can provide a high
capacitance, low-cost solution. The bulk capacitance provides
minimal output voltage drop/soar after load transients occur.
Input Capacitor Selection
Typically, the input impedance is so low (or has other input
capacitance distributed throughout the system) that a single
22 F (X7R or X5R) ceramic capacitor located near the SKY87203
is sufficient. However, additional input capacitance may be
necessary depending on the impedance of the input supply.
Always examine the ceramic capacitor DC voltage coefficient
characteristics when evaluating ceramic bypass capacitors.
Besides the capacitance requirement, the RMS current rating of
the input capacitor must be able to support the pulsed current
drawn by the step-down regulator. The input RMS current
requirement may be determined by:
VOUT
V
1 OUT
VIN
VIN
I RMS ( MAX )
I OUT
2
The input capacitor provides a low impedance loop for the pulsed
current drawn by the SKY87203. Low ESR/ESL (X7R and X5R)
ceramic capacitors are ideal for this function. To minimize stray
inductance, the capacitor should be placed as close as possible to
the high-side MOSFET. This keeps the high frequency content of
the input current localized, minimizing EMI and input voltage
ripple. The proper placement of the input capacitor can be seen in
the Evaluation Board layout.
Recommended input capacitors are listed in Table 7.
Layout Recommendations
Make the power trace as short and wide as possible, including
the input/output power lines and switching node, etc.
VOUT
V
1 OUT
VIN
V
D 1 D
IN
VPP
VPP
ESR f SW
ESR f SW
I
I
OUT
OUT
I RMS I OUT
1
V
4 PP ESR f SW
I OUT
For best performance of the SKY87203, the following guidelines
should be followed when designing the PCB layout:
To estimate the required input capacitance, determine the
acceptable input ripple level (VPP) and solve the following
equation:
C IN
C IN
I OUT D 1 D
The terms D and “1 – D” appear in both input ripple voltage and
input capacitor RMS current equations. The maximum value for D
occurs when VOUT = 0.5 × VIN (50 percent duty cycle). This results
in a set of “worst case” capacitance and RMS current design
requirements:
While the two-layer PCB is enough for most applications, large
and integral multilayer ground planes are ideal for high-power
applications. Large areas of copper have lower resistance and
help to dissipate heat.
Put the input and output capacitor as close as possible to the IC
to get the best filter result.
Feedback and shutdown circuits should not be close to large AC
signals involving the power inductor and switching node. Place
the feedback resistors close to the output terminals.
Connect the analog and power grounds together with a single
short line. Connect all low-current loop grounds to analog
ground to decrease the power ground noise on the analog
ground and to achieve better load regulation.
Table 7. Recommended Input/Output Capacitor Selection
Manufacturer
Part Number
Capacitance
(F)
Voltage
(V)
Temperature Coefficient
Case
Murata
GRM188R71H104KA93D
0.1
50.0
X7R
0603
Murate
GRM21BR70J106ME76
10.0
6.3
X7R
0805
Murata
GRM219R61A226MEA0
22.0
10.0
X5R
0805
Murate
GRM1885C1H220JA01
22.0
50.0
C0G
0603
KEMET
T520D477M006ATE025
470.0
6.3
±20% Tol, –55 °C to +105 °C
7343
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13
DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
Evaluation Board Description
Package and Handling Information
The SKY87203 Evaluation Board is used to test the performance
of the SKY87203 step-down DC-DC converter. An Evaluation
Board schematic diagram is provided in Figure 26. Layer details
for the SKY87203 Evaluation Board are shown in Figure 27.
Component values for the SKY87203 Evaluation Board are listed
in Table 8.
Instructions on the shipping container label regarding exposure to
moisture after the container seal is broken must be followed.
Otherwise, problems related to moisture absorption may occur
when the part is subjected to high temperature during solder
assembly.
Package Dimensions
The PCB layout footprint for the SKY87203 is provided in
Figure 28. Typical case markings for the SKY87203 are shown in
Figure 29. Package dimensions for the 12-pin, 2 mm 2 mm
QFN package are shown in Figure 30. Tape and reel dimensions
are shown in Figure 31.
The SKY87203 is rated to Moisture Sensitivity Level 1 (MSL1) at
260 C. It can be used for lead or lead-free soldering. For
additional information, refer to the Skyworks Application Note,
Solder Reflow Information, and document number 200164.
Care must be taken when attaching this product, whether it is
done manually or in a production solder reflow environment.
Production quantities of this product are shipped in a standard
tape and reel format.
Switch Node
SKY87203
10
Supply Voltage
C1_1
Bulk Cap
(optional)
C1
22 μF
R4
274 kΩ
8
C4 (optional)
1 μF
Power Good
VIN
EN
PG
AGND
9
PVIN
4
LX
OUT
FB
FSET
PGND
1
2, 11
L1
1 μH
C2
22 μF
6
R1
294 kΩ
7
Output Voltage
3.6 V
C3
(optional)
R2
57.6 kΩ
5
R3
(optional)
3, 12
t0284
Figure 26. SKY87203 Evaluation Board Schematic
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
Top Layer
Detailed View
Bottom Layer
t0593
Figure 27. SKY87203 Evaluation Board Assembly Drawing
Table 8. Evaluation Board Bill of Materials (BOM)
Component
Value
Part Number
Manufacturer
Description
C1, C2
22 F
GRM219R61A226MEA0
Murata
Ceramic, 0805, X5R, 10 V, 20%
R1
294 k
RC0603FR-07294KL
Yageo
1/10 W, 1%, 0603, SMD
R2
57.6 k
RC0603FR-07457K6L
Yageo
1/10 W, 1%, 0603, SMD
R4
274 k
RC0603FR-07274KL
Yageo
1/10 W, 1%, 0603, SMD
L1
1 H
0520CDMCDS-1R0MC
Sumida
8 A, 17 m, SMD
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15
DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
8X 0.650
Pin 10
10X 0.450
10X 0.250
Pin 1
2X 0.125
4X 0.250
4X 0.750
2X 0.250
1.750
2X 0.650
Exposed soldering area
2X 0.500
4X 1.750
Notes:
1. All dimensions are in millimeters.
2. The suggested land pattern should be used as a guideline only.
3. The assembly house should use a land pattern that fits their SMT process and environment.
4. Some of the key factors that affect the land pattern and solder stencil aperture opening
are solder paste size, solder stencil thickness, and reflow profile.
t0587
Figure 28. SKY87203 PCB Layout Footprint
Pin 1
Indicator
Skyworks
Part #
t0293-2
Figure 29. SKY87203 Typical Case Markings
(Top View)
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
2X 0.500 ± 0.050
0.05 M C A B
4X 0.200 Min.
2
Pin 1 Indicator
Chamfer 0.100 X 45°
A
B
Pin 1
Indicator
2X 0.250 ± 0.050
0.05 M C A B
2
0.500 BSC
2X 0.200 Min.
0.05 C
2X
10X 0.350 ± 0.050
2X
10X 0.250 ± 0.050
0.10 M C A B
0.05 M C
0.05 C
Bottom View
Top View
0.050 C
0.850 ± 0.050
C
Seating Plane
0.203 Ref.
0 – 0.05
0.080 C
10X
Side View
All measurements are in millimeters.
S3183
Figure 30. SKY87203 12-Pin QFN Package Dimensions
4.0 ± 0.1 (P0)
(Note 2)
2.0 ± 0.05 (P2)
(Note 1)
1.75 ± 0.1 (E1)
ø1.5 ± 0.1 (D0)
X
ø1.0 ± 0.25 (D1)
CL
X
2.30 ± 0.05 (Bo)
1.00 ± 0.05 (Ko)
Y
8.00 +0.3/–0.1
Y
3.50 ± 0.05
(Note 1)
0.25 ± 0.02 (T)
Pin1
Location
Y
4.00 ± 0.1 (P1)
2.30 ± 0.05 (A0)
10° Max.
Notes:
1. Measured from centerline of sprocket hole to centerline of pocket.
2. 10 sprocket hole pitch cumulative tolerance ±0.2.
3. ESD-surface resistivity is a maximum of 1 x 109 Ohms/square per EIA,
JEDEC TNR Specification.
4. All measurements are in millimeters.
CL
X
S3188
Figure 31. SKY87203 Tape and Reel Dimensions
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DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER
Ordering Information
Model Name
SKY87203 Step-Down DC-DC Converter
Manufacturing Part Number
SKY87203-11-631LF
Evaluation Board Part Number
SKY87203-11-631LF-EVB
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