ST PM8903 User Manual
3 A step-down monolithic switching regulator
Features
■ Integrated 35 mΩ MOSFETs for high efficiency
■ 3 A continuous output current
■ 2.8 V to 6 V input voltage (VIN)
■ 2.9 V to 5.5 V supply voltage (VCC)
■ Adjustable output voltage down to 0.6 V
■ 1% output voltage accuracy
■ 1.1 MHz switching frequency operation
■ PSKIP mode to optimize light load efficiency
■ Embedded bootstrap diode
■ Thermally compensated loss-less current
sense across HS and LS MOSFETs
■ OV/UV/OC and overtemperature protection
■ Internal soft-start and soft-stop
■ Interleaving synchronization (Up to 2 ICs)
■ Power Good output
■ Shutdown function (<15 μA quiescent current)
■ VFQFPN16 3 x 3 mm compact package
Applications
■ Subsystem power supply
■ CPU, DSP and FPGA power supply
■ Distributed power supply
■ General DC-DC converters
PM8903
VFQFPN16 3x3 mm
Description
The PM8903 is a high efficiency monolithic stepdown switching regulator designed to deliver up to
3 A continuous current. The IC operates from 2.8
V to 6 V input voltage (VIN).
The PM8903 features low-resistance integrated
nMOS and proprietary pulse-skipping mode for
optimum efficiency over all the loading range.
The voltage mode control loop allows the widest
range of output filter. Current sense is internally
thermally compensated for optimum precision.
The integrated 0.6 V reference allows the
regulation of output voltages with ±1% accuracy
over temperature variations. Switching frequency
is typically set to 1.1 MHz and can be
programmed to 0.8 MHz or 1.0 MHz. Out of phase
synchronization allows the reduction of input RMS
current.
The PM8903 provides precise dual-threshold
overcurrent protection as well as over /
undervoltage and overtemperature protection.
PGOOD output easily provides real-time
information on the output voltage.
The PM8903 is available in VFQFPN16 3 x 3 mm.
Table 1. Device summary
Order codes Package Packing
PM8903 VFQFPN16 3x3 mm Tube
PM8903TR VFQFPN16 3x3 mm Tape and reel
February 2012 Doc ID 022748 Rev 1 1/34
www.st.com
34
Contents PM8903
Contents
1 Typical application circuit and block diagram . . . . . . . . . . . . . . . . . . . . 3
1.1 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Pin description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2 Recommended operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.4 Typical operating characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1 Power section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.2 Startup and shutdown management . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2.1 Low-side-less startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2.2 Soft-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3 Output voltage monitoring and protection . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3.1 Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3.2 Undervoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.3.3 Feedback disconnection protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.3.4 Power Good (PGOOD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.4 Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.5 Overtemperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.6 Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.7 Pulse-skipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.8 Multifunction pin PSKIP/MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.1 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
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PM8903 Contents
6.2 Output voltage setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.3 Inductor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.4 Output capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.5 Input capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7 PM8903 demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.1 Detailed demonstration board description . . . . . . . . . . . . . . . . . . . . . . . . 23
7.1.1 Power input (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.1.2 Signal input (VCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1.3 Output (VOUT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1.4 Test points and jumper connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Doc ID 022748 Rev 1 3/34
Typical application circuit and block diagram PM8903
1 Typical application circuit and block diagram
1.1 Application circuit
Figure 1. Typical application circuit
1.2 Block diagram
Figure 2. Block diagram
4/34 Doc ID 022748 Rev 1
PM8903 Pin description and connection diagrams
2 Pin description and connection diagrams
Figure 3. Pin connection (top view)
PGND
PGND
VIN
VIN
16 15 14 13
EN
SYNCH
PGOOD
BOOT
1
2
3
4
5678
PHASE
PHASE
PHASE
12
11
10
9
PSKIP / MS
VCC
GND
FB
COMP
2.1 Pin description
Table 2. Pin description
Pin# Name Function
Enable. Internally pulled up by 5 μA to VCC.
1EN
2 SYNCH
3 PGOOD
4BOOT
5 to 7 PHASE
Force low to disable the device, set free or pull up above turn-on threshold to
enable the converter operations.
Synchronization pin.
According to PSKIP status, the IC sends the synchronization signal out of this
pin when master, while accepting a synchronization signal when slave.
Connect to the same SYNCH pin of a similar part when synchronizing ICs.
In case of single IC operation, leave floating.
Open drain output set free after SS has finished and pulled low when VOUT is
out of the PGOOD window or any protection is triggered.
Pull up to a voltage lower than VCC, if not used it can be left floating.
Bootstrap pin.
It provides power supply for the floating high-side driver. Connect with 0.1 μF
to PHASE. See
Output inductor connection.
The pins are connected to the embedded MOSFETs (high-side source and
low-side drain). Connect directly to output inductor. See
Figure 1
.
Figure 1
.
Doc ID 022748 Rev 1 5/34
Pin description and connection diagrams PM8903
Table 2. Pin description (continued)
Pin# Name Function
Pulse-skip and master/slave definition.
Connect with a resistor to GND or leave it floating to define:
8 PSKIP / MS
9COMP
10 FB
11 GND
Pulse-skip feature status;
Master/slave for synchronization;
Switching frequency.
See
Section 5.8 on page 18
.
Error amplifier output.
Connect with an (R
- CF) // CP to FB. See
F
Figure 1
The device cannot be disabled by pulling low this pin.
Error amplifier inverting input.
Connect with R
COMP. A resistor R
or RFB // (RS - CS) to VSEN and with an (RF - CF) // CP to
FB
to GND sets the output voltage ratio. See
OS
Figure 1
All the internal references are referred to this pin. Connect to the PCB Signal
Ground.
12 VCC
13, 14 VIN
15, 16 PGND
Thermal pad
Device power supply.
Operative voltage is 2.9 V - 5.5 V. Filter with at least 1 μF MLCC vs. GND.
Power input voltage, connected to embedded high-side drain.
Supply range is from 2.8 V to 6 V. Bypass VIN pins to PGND pins close to the
IC package with high quality MLCC capacitors (at least 10 μF). See
Figure 1
Power ground connection, connected to embedded low-side MOSFET source.
Connect to PGND PCB plane. See
Figure 1
.
Thermal pad connects the silicon substrate and makes good thermal contact
with the PCB. Connect to the PCB PGND plane.
.
6/34 Doc ID 022748 Rev 1
PM8903 Thermal data
3 Thermal data
Table 3. Thermal data
Symbol Parameter Value Unit
Thermal resistance junction to ambient
R
thJA
(Device soldered on standard demonstration board, see
Chapter 7 on page 24
for details)
30 °C/W
R
T
T
thJC
MAX
STG
T
J
Thermal resistance junction to case 12 °C/W
Maximum junction temperature 150 °C
Storage temperature range -40 to 150 °C
Junction temperature range -25 to 125 °C
Doc ID 022748 Rev 1 7/34
Electrical specifications PM8903
4 Electrical specifications
4.1 Absolute maximum ratings
Table 4. Absolute maximum ratings
Symbol Parameter Value Unit
to PGND, GND -0.3 to 6 V
to PGND, GND -0.3 to 7 V
to PGND, GND
to PHASE
to PGND, GND
to PGND, GND, VIN=6 V, t<100 nsec.
to PGND, GND -0.3 to 7 V
to PGND, GND -0.3 to 6 V
EN
V
V
V
SYNCH
V
CC
V
IN
V
BOOT
PHASE
PGOOD
, V
All other pins to GND -0.3 to 3.6 V
4.2 Recommended operating conditions
Table 5. Recommended operating conditions
Symbol Parameter Min. Typ. Max. Unit
V
IN
V
CC
Power supply voltage 2.8 - 6 V
Signal supply voltage 2.9 - 5.5 V
-0.3 to 13
-0.3 to 6
-0.3 to 7
-1.7 to 7.5
V
V
8/34 Doc ID 022748 Rev 1
PM8903 Electrical specifications
4.3 Electrical characteristics
VIN = V
= 3.3 V ± 5%, TJ = 0 °C to 125 °C, typical values at TJ = 25 °C, unless otherwise
CC
specified.
Table 6. Electrical characteristics
Symbol Parameter Test conditions Min. Typ. Max. Unit
Supply current and undervoltage lockout
I
I
CC
I
SHUTDOWN
VIN UVLO
VCC UVLO
Oscillator
F
SW
ΔV
OSC
d Duty cycle
T
ON-min
T
OFF-min
Reference and error amplifier
IN
VIN supply current Switching, no inductor connected 5 mA
VCC supply current Switching, no inductor connected 1 mA
VCC + VIN supply current Shutdown, EN = 0 V 7 μA
VIN turn-ON VIN rising 2.8 V
Hysteresis 100 mV
Deglitching
(1)
Rising and falling edge 1 μs
VCC turn-ON VCC rising 2.9 V
Hysteresis 100 mV
(1)
(1)
(1)
(1)
Rising and falling edge 1 μs
=0 Ω / 24 kΩ / 180 kΩ / 240 kΩ
R
PM
or PSKIP/MS pin floating
(1)
0.99 1.1 1.21 MHz
1V
0100%
80 ns
80 ns
Deglitching
Main oscillator accuracy
PWM ramp amplitude
Minimum ON time
Minimum OFF time
Output voltage accuracy VOUT = 0.6 V -1 - 1 %
A
0
DC gain
(1)
GBWP Gain-bandwidth product
SR Slew-rate
(1)
Output power MOSFETS
HS R
LS R
DS-on
DS-on
HS drain-source ON
resistance
LS drain-source ON
resistance
Overcurrent protection
I
OC1
I
OC2
1st level overcurrent
threshold
2nd level overcurrent
threshold
(1)
120 dB
(1)
C
=20 pF 5 V/μs
COMP
14 MHz
35 mΩ
35 mΩ
HS sourcing 4.0 4.6 5.2 A
HS sourcing 4.5 5.2 5.9 A
Doc ID 022748 Rev 1 9/34
Electrical specifications PM8903
Table 6. Electrical characteristics (continued)
Symbol Parameter Test conditions Min. Typ. Max. Unit
Over and undervoltage protections
OVP OVP threshold
FB rising 0.69 0.72 0.75 V
LS turns off, FB falling 0.30 V
UVP UVP threshold FB falling 0.45 0.48 0.51 V
I
FB
FB disconnection bias
current
Sourced from FB 100 nA
Overtemperature protection
Thermal shutdown
threshold
(1)
140 °C
OTP
Thermal shutdown
hysteresis
(1)
40 °C
PGOOD
Upper threshold FB rising 0.69 0.72 0.75 V
PGOOD
Lower threshold FB falling 0.45 0.48 0.51 V
V
PGOODL
PGOOD voltage low I
= -4 mA 0.4 V
PGOOD
ENABLE
Input logic high EN rising 1.5 V
Input logic low EN falling 0.65 V
EN
Hysteresis 150 mV
Deglitching
(1)
Rising and falling edge 3 μs
SS
=0 Ω / 24 kΩ / 180 kΩ / 240 kΩ
R
T
SS
1. Guaranteed by design, not subject to test.
Soft-start time
PM
or PSKIP/MS pin floating
10/34 Doc ID 022748 Rev 1
0.79 ms
PM8903 Electrical specifications
4.4 Typical operating characteristics
(The demonstration board as described in
V, VOUT=1V5, T
= 25 °C, unless otherwise specified.)
J
Figure 4. Efficiency vs. output current -
V
= 3.3 V
Figure 6. Load regulation - VIN = 3.3V Figure 7. Load regulation - V
IN
Chapter 7.1 on page 25
, R
=0 Ω, V
PM
Figure 5. Efficiency vs. output current -
V
= 5 V
IN
IN
IN
= 5 V
= V
CC
= 3.3
Doc ID 022748 Rev 1 11/34
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