ST PM6675S User Manual
Features
■ Switching section
– 4.5 V to 28 V input voltage range
– 0.6 V, ±1 % voltage reference
– Selectable 1.5 V fixed output voltage
– Adjustable 0.6 V to 3.3 V output voltage
– 1.237 V ±1 % reference voltage available
– Very fast load transient response using
constant on-time control loop
–No R
MOSFETs' R
– Negative current limit
– Latched OVP and UVP
– Soft-start internally fixed at 3 ms
– Selectable pulse skipping at light load
– Selectable No-Audible (33 kHz) pulse skip
mode
– Ceramic output capacitors supported
– Output voltage ripple compensation
– Output soft-end
■ LDO regulator section
– Adjustable 0.6 V to 3.3 V output voltage
– Selectable ±1 Apk or ±2 Apk current limit
– Dedicated power-good signal
– Ceramic output capacitors supported
– Output soft-end
current sensing using low side
SENSE
DS(ON)
PM6675S
High efficiency step-down controller
with embedded 2 A LDO regulator
VFQFPN-24 4x4
Description
The PM6675S device consists of a single high
efficiency step-down controller and an
independent Low Drop-Out (LDO) linear
regulator.
The Constant On-Time (COT) architecture
assures fast transient response supporting both
electrolytic and ceramic output capacitors. An
embedded integrator control loop compensates
the DC voltage error due to the output ripple.
A selectable low-consumption mode allows the
highest efficiency over a wide range of load
conditions. The low-noise mode sets the minimum
switching frequency to 33 kHz for audio-sensitive
applications.
The LDO linear regulator can sink and source up
to 2 Apk. Two fixed current limits (±1 A-±2 A) can
be chosen.
Applications
■ Notebook computers
■ Graphic cards
■ Embedded computers
Table 1. Device summary
Order codes Package Packaging
PM6675S
PM6675STR Tape and reel
February 2008 Rev 1 1/53
VFQFPN-24 4x4 (exposed pad)
An active soft-end is independently performed on
both the switching and the linear regulators
outputs when disabled.
Tu b e
www.st.com
Contents PM6675S
Contents
1 Typical application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Recommended operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Typical operating characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7 Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1 Switching section - constant on-time PWM controller . . . . . . . . . . . . . . . 20
7.1.1 Constant-On-Time architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.1.2 Output ripple compensation and loop stability . . . . . . . . . . . . . . . . . . . . 23
7.1.3 Pulse-skip and no-audible pulse-skip modes . . . . . . . . . . . . . . . . . . . . . 27
7.1.4 Mode-of-operation selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1.5 Current sensing and current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.1.6 POR, UVLO and Soft Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1.7 Switching section power good signal . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
7.1.8 Switching section output discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
7.1.9 Gate drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.1.10 Reference voltage and bandgap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.1.11 Switching section OV and UV protections . . . . . . . . . . . . . . . . . . . . . . . 33
7.1.12 Device thermal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2/53
PM6675S Contents
7.2 LDO linear regulator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.2.1 LDO section current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.2.2 LDO section Soft-Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.2.3 LDO section power good signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.2.4 LDO section output discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
8 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
8.1 External components selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
8.1.1 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
8.1.2 Input capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
8.1.3 Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
8.1.4 MOSFETs selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
8.1.5 Diode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
8.1.6 VOUT current limit setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
8.1.7 All ceramic capacitors application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3/53
Typical application circuit PM6675S
1 Typical application circuit
Figure 1. Application circuit
V
LDOIN
LDO PG
V
LDO
10
C
IN4
C
OUT2
VSEL
23
LIN
4
LPG
24
LOUT
2
LFB
1
LGND
SMPS PG
R
LP
C
IN3
312618822
LILIM
NOSKIP
SGND
5151413 711
AVCC
PM6675S
PM6675
LEN
SPG
C
B
O
O
VCC
SWEN
HGATE
VOSC
T
PHASE
LGATE
VREF
COMP
C
BYP
IN2
CSNS
PGND
VSNS
21
20
17
19
16
9
+5V
C
BOOT
V
BATT
R
1
C
R
2
IN
L
V
SMPS
C
R
LIM
OUT
C
INT
4/53
PM6675S Pin settings
2 Pin settings
2.1 Connections
Figure 2. Pin connection (through top view)
LOUT
LIN
24
1
LGND
BOOT
HGATE
PHASE
CSNS
19
18
VCC
LFB
NOSKIP
LPG
SGND
AVCC
LGATE
PM6675
PM6675S
6
7
VREF
VOSC
VSNS
VSEL
12
LILIM
COMP
PGND
SPG
LEN
SWEN
13
5/53
Pin settings PM6675S
2.2 Pin description
Table 2. Pin functions
N° Pin Function
1LGND
2LFB
3NOSKIP
4LPG
5SGND
6AVCC
7VREF
8VOSC
9 VSNS
10 VSEL
11 COMP
12 LILIM
LDO power ground. Connect to the negative terminal of VTT output
capacitor.
LDO remote sensing. Connect as close as possible to the load via a low
noise PCB trace.
Pulse-Skip/No-Audible Pulse-Skip Modes selector.
See Section 7.1.4: Mode-of-operation selection on page 30
LDO section power-good signal (open drain output). High when LDO output
voltage is within ±10 % of nominal value.
Ground reference for analog circuitry, control logic and VTTREF buffer.
Connect together with the thermal pad and VTTGND to a low impedance
ground plane. See the Application Note for details.
+5 V supply for internal logic. Connect to +5 V rail through a simple RC
filtering network.
High accuracy output voltage reference (1.237 V) for multilevel pins setting.
It can deliver up to 50 µA. Connect a 100 nF capacitor between VREF and
SGND in order to enhance noise rejection.
Frequency selection. Connect to the central tap of a resistor divider to set
the desired switching frequency. The pin cannot be left floating. See
Section 7: Device description on page 19 for details.
Switching section output remote sensing and discharge path during output
soft-end. Connect as close as possible to the load via a low noise PCB
trace.
Fixed output selector and feedback input for the switching controller.
If VSEL pin voltage is higher than 4 V, the fixed 1.5 V output is selected. If
VSEL pin voltage is lower than 4 V, it is used as negative input of the error
amplifier. See Section 7.1.4: Mode-of-operation selection on page 30 for
details.
DC voltage error compensation input pin for the switching section. Refer to
Section 7.1.4: Mode-of-operation selection on page 30 for more details.
Current limit selector for the LDO. Connect to SGND for ±1 A current limit or
to +5 V for ±2 A current limit.
13 SWEN
14 LEN
15 SPG
16 PGND Power ground for the switching section.
17 LGATE Low-side gate driver output.
18 VCC +5 V low-side gate driver supply. Bypass with a 100 nF capacitor to PGND.
6/53
Switching controller enable. When tied to ground, the switching output is
turned off and a soft-end is performed.
Linear regulator enable. When tied to ground, the LDO output is turned off
and a soft-end is performed.
Switching section power good signal (open drain output). High when the
switching regulator output voltage is within ±10 % of nominal value.
PM6675S Electrical data
Table 2. Pin functions (continued)
N° Pin Function
Current sense input for the switching section. This pin must be connected
19 CSNS
20 PHASE Switch node connection and return path for the high side gate driver.
21 HGATE High-Side Gate Driver Output
22 BOOT
through a resistor to the drain of the synchronous rectifier (R
DS(ON)
sensing)
to set the current limit threshold.
Bootstrap capacitor connection. Input for the supply voltage of the high-side
gate driver.
23 LIN
24 LOUT
Linear Regulator Input. Bypass to LGND by a 10µF ceramic capacitor for
noise rejection enhancement.
LDO linear regulator output. Bypass with a 20µF (2 x 10 µF MLCC) filter
capacitor.
3 Electrical data
3.1 Maximum rating
Table 3. Absolute maximum ratings
Symbol Parameter Value Unit
V
AVC C
V
VCC
V
PHASE
1. Free air operating conditions unless otherwise specified. Stresses beyond those listed under "absolute
maximum ratings" may cause permanent damage to the device. Exposure to absolute maximum rated
conditions for extended periods may affect device reliability.
AVCC to SGND -0.3 to 6
VCC to SGND -0.3 to 6
PGND, LGND to SGND -0.3 to 0.3
HGATE and BOOT to PHASE -0.3 to 6
HGATE and BOOT to PGND -0.3 to 44
PHASE to SGND -0.3 to 38
LGATE to PGND -0.3 to V
CSNS, SPG, LEN, SWEN, LILIM, COMP, VSEL,
VSNS, VOSC, VREF, NOSKIP to SGND
LPG,VREF, LOUT, LFB to SGND -0.3 to V
LIN, LOUT, LPG, LIN to LGND -0.3 to V
Maximum withstanding Voltage range test
condition: CDF-AEC-Q100-002- “Human Body
Model” acceptance criteria: “Normal
Performance”
(1)
CC
-0.3 to V
AVC C
AVC C
AVC C
± 1250 V
V
+0.3
+ 0.3
+ 0.3
+ 0.3
7/53
Electrical data PM6675S
3.2 Thermal data
Table 4. Thermal data
Symbol Parameter Value Unit
R
T
thJA
STG
T
A
T
J
Thermal resistance junction to ambient 42 °C/W
Storage temperature range - 50 to 150 °C
Operating ambient temperature range - 40 to 85 °C
Junction operating temperature range - 40 to 125 °C
3.3 Recommended operating conditions
Table 5. Recommended operating conditions
Symbol Parameter
V
AVC C
V
VCC
IN
Input voltage range 4.5 28
IC supply voltage 4.5 5.5
IC supply voltage 4.5 5.5
Val ues
Unit
Min Typ Max
VV
8/53
PM6675S Electrical characteristics
4 Electrical characteristics
Table 6. Electrical characteristics
T
= 0 °C to 85 °C, VCC = AVCC = +5 V, LIN = 1.5 V and LOUT = 0.6 V, if not otherwise
A
specified
(1)
Symbol Parameter Test condition
Supply section
I
IN
Operating current
(Switching + LDO)
SWEN, LEN, VSEL and
NOSKIP connected to AVCC,
No load on LOUT output.
SWEN, VSEL and NOSKIP
I
SW
Operating current (Switching)
connected to AVCC, LEN
connected to SGND.
I
SHDN
Shutdown operating current SWEN and LEN tied to SGND. 10 µA
AVCC under voltage lockout
upper threshold
UVLO
AVCC under voltage lockout
upper threshold
UVLO hysteresis 70 mV
ON-time (SMPS)
Val ues
Unit
Min Typ Max
2
mA
1
4.1 4.25 4.4
V
3.85 4.0 4.1
t
ON
On-time duration
OFF-time (SMPS)
t
OFFMIN
Minimum OFF-time 300 350 ns
Volt a g e re f e r enc e
Voltage accuracy 4.5 V< V
Load regulation -50 µA< I
Undervoltage Lockout Fault
Threshold
VSEL low,
VOSC=300 mV 530 630 730
NOSKIP low,
V
VSNS
= 2V
VOSC=500 mV 320 380 440
< 25 V 1.224 1.237 1.249 V
IN
< 50 µA -4 4
VREF
800
ns
mV
9/53
Electrical characteristics PM6675S
Table 6. Electrical characteristics (continued)
T
= 0 °C to 85 °C, VCC = AVCC = +5 V, LIN = 1.5 V and LOUT = 0.6 V, if not otherwise
A
specified
Symbol Parameter Test condition
SMPS output
(1)
Val ues
Unit
Min Typ Max
V
OUT
SMPS fixed output voltage
Feedback output voltage
accuracy
VSEL connected to AVCC,
NOSKIP tied to SGND, No Load
-1.5 1.5 %
1.5 V
Current limit and zero crossing comparator
I
CSNS
CSNS input bias current 90 100 110 µA
Comparator offset -6 6
V
ZC,OFFS
Positive current limit threshold V
Fixed negative current limit
threshold
Zero crossing comparator
offset
PGND
- V
CSNS
100
110
-11 -5 1
High and low side gate drivers
HGATE high state (pull-up) 2.0 3
HGATE driver on-resistance
HGATE low state (pull-down) 1.8 2.7
LGATE high state (pull-up) 1.4 2.1
LGATE driver on-resistance
LGATE low state (pull-down) 0.6 0.9
UVP/OVP protections and PGOOD signals
OVP Over voltage threshold 112 115 118
UVP Under voltage threshold 67 70 73
SMPS upper threshold 107 110 113
SMPS lower threshold 86 90 93
PGOOD
LDO upper threshold 107 110 113
LDO lower threshold 86 90 93
mV
Ω
%
I
PG,LEAK
V
PG,LOW
SPG and LPG Leakage
Current
SPG and LPG Low Level
Voltage
and LPG forced to 5.5 V 1 µA
SPG
I
LPG,SINK
= I
SPG,SINK
= 4 mA 150 250 mV
Soft-start section (SMPS)
Soft-start ramp time
(4 steps current limit)
234ms
Soft-start current limit step 25 µA
10/53
PM6675S Electrical characteristics
Table 6. Electrical characteristics (continued)
T
= 0 °C to 85 °C, VCC = AVCC = +5 V, LIN = 1.5 V and LOUT = 0.6 V, if not otherwise
A
specified
Symbol Parameter Test condition
Soft-end section
(1)
Val ues
Unit
Min Typ Max
LDO section
V
LREF
I
LDO,CL
I
LIN,BIAS
I
LFB,BIAS
I
LFB,LEAK
Switching section discharge
resistance
LDO section discharge
resistance
15 25 35
15 25 35
LDO reference voltage 600
LDO output accuracy respect
to VREF
LDO sink current limit
LDO source current limit
LDO input bias current, ON
-1 mA < I
-1 A < I
V
> V
LFB
> V
V
LFB
0.9 • V
LILIM = 5V
0.9 • V
LILIM = 0V
< 0.9 • V
V
LFB
< 0.9 • V
V
LFB
LEN connected to AVCC, no
load
< 1 mA -20 20
LDO
< 1 A -25 25
LDO
, LILIM = 5 V -3 -2.3 -2
LREF
, LILIM = 0 V -1.6 -1.3 -1
LREF
< V
LREF
LREF
< V
LFB
< V
< V
LFB
, LILIM = 5 V 1 1.3 1.6
LREF
, LILIM = 0 V 0.5 0.8 1.1
LREF
LREF
LREF
,
,
22.43
11.31.6
110
LDO input bias current, OFF LEN = 0 V, no load 1
LFB input bias current
LEN connected to AVCC
= 0.6 V
V
LFB
LFB leakage current LEN = 0 V, V
= 0.6 V -1 1
LFB
-1 1
Ω
mV
A
µA
11/53
Electrical characteristics PM6675S
Table 6. Electrical characteristics (continued)
T
= 0 °C to 85 °C, VCC = AVCC = +5 V, LIN = 1.5 V and LOUT = 0.6 V, if not otherwise
A
specified
Symbol Parameter Test condition
Power management section
V
VTHVSEL
V
VTHNOSKIP
VSEL pin thresholds
NOSKIP pin thresholds
(1)
Val ues
Min Typ Max
V
Fixed mode
Adjustable mode
Forced-PWM mode
No-audible mode 1.0
AVC C
-0.7
V
AVC C
-
0.8
V
AVC C
-
1.3
V
AVC C
-
1.5
Pulse-skip mode 0.5
Unit
V
V
VTHLEN
V
VTHSWEN
V
VTHLILIM
LEN, SWEN turn off level 0.4
,
LEN, SWEN turn on level 1.6
V
LILIM pin thresholds
±2 A LDO current limit
AVC C
-0.8
±1 A LDO current limit 0.5
I
IN,LEAK
IN3,LEAK
I
OSC,LEAK
Logic input leakage current LEN, SWEN and LILIM = 5 V 10
Multilevel input leakage
current
VSEL and NOSKIP = 5 V 10
VOSC pin leakage current VOSC = 1 V 1
Thermal shutdown
T
SHDN
1. TA = TJ. All parameters at operating temperature extremes are guaranteed by design and statistical analysis
(not production tested)
2. Guaranteed by design. Not production tested.
Shutdown temperature
(2)
150 °C
µAI
12/53
PM6675S Typical operating characteristics
5 Typical operating characteristics
Figure 3. VOUT efficiency vs load, 1.5 V,
100
90
80
70
60
50
40
Eff ici ency [%]
30
20
10
0
0.01 0.10 1.00 10.00
SW frequency = 400 kHz
SKIP @ 8V
SKIP @ 12V
SKIP @ 16V
No Aud. SKIP @ 8V
No Aud. SKIP @ 12 V
No Aud. SKIP @ 16 V
PWM @ 8V
PWM @ 12V
PWM @16V
Output Current [A]
Figure 4. VOUT efficiency vs load, 1.25 V,
SW frequency = 400 kHz
100
90
80
70
60
50
40
30
Efficiency [%]
20
10
0
0.01 0.10 1.00 10.00
Output Current [A]
SKIP @ 8V
SKIP @ 12V
SKIP @ 16V
No Aud. SKIP @ 8V
No Aud. SKIP @ 12V
No Aud. SKIP @ 16V
PWM @ 8V
PWM @ 12V
PWM @ 16V
Figure 5. VOUT load regulation, 1.5 V,
1.54
1.53
1.52
1.51
1.50
Output Volt age [ V]
1.49
1.48
Vin = 12 V
PWM
No Aud. SKIP
SKIP
0.01 0.10 1.00 10.00
Output Current [A]
Figure 7. VOUT load regulation, 2.5 V,
2.56
2.55
2.54
2.53
2.52
2.51
2.50
Output Voltage [V ]
2.49
2.48
Vin = 12 V
PWM
No A u d. S KIP
SKIP
0.01 0.1 1 10
Output Curre nt [A]
Figure 6. VOUT load regulation, 1.25 V,
Vin = 12 V
1.280
1.275
1.270
1.265
1.260
PWM
No Aud. SKIP
SKIP
1.255
1.250
Output Voltage [V]
1.245
1.240
0.01 0.10 1.00 10.00
Output Curre nt [A]
Figure 8. LOUT load regulation, LOUT = 0.9 V,
LIN = 1.5 V
0.94
0.93
0.92
0.91
0.90
LOUT [V]
0.89
0.88
0.87
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Output Curre nt [A]
13/53
Typical operating characteristics PM6675S
Figure 9. VOUT line regulation, 1.5 V, 0 A Figure 10. VOUT line regulation, 1.25 V, 0 A
1.540
1.535
1.530
1.525
1.520
1.515
Output Voltage [V]
1.510
0 102030
SKIP @ 0A
No Aud. SKIP @ 0A
PWM @ 0A
Input Voltage [V]
Figure 11. VOUT line regulation, 1.5 V Figure 12. VOUT line regulation, 1.25 V
1.5170
1.5165
1.5160
1.5155
1.5150
1.5145
1.5140
Output Voltage [V]
1.5135
1.5130
0 5 10 15 20 25 30
PWM @ 0A
PWM @ 7A
Input Voltage [V]
1.285
1.280
1.275
1.270
1.265
Output Voltage [V]
1.260
0 102030
Input Voltage [V]
1.2660
1.2655
1.2650
1.2645
1.2640
1.2635
Output Voltage [V]
1.2630
1.2625
0 5 10 15 20 25 30
Input Voltage [V]
SKIP @ 0A
No Aud. SKIP @ 0A
PWM @ 0 A
PWM @ 0 A
PWM @ 7 A
Figure 13. Switching frequency vs input
600
550
500
450
400
fsw [kHz ]
350
300
250
voltage, 1.5 V
PWM @ 0A
PWM @ 7A
0 5 10 15 20 25 30
Input Voltage [V]
Figure 14. Switching frequency vs input
voltage, 1.25 V
600
550
500
450
400
350
fsw [kHz ]
300
250
200
0 5 10 15 20 25 30
Input Voltage [V]
PWM @ 0 A
PWM @ 7 A
14/53
PM6675S Typical operating characteristics
Figure 15. Switching frequency vs load - 1.5 V Figure 16. PWM waveforms
600
500
400
300
fsw [kHz]
200
100
0
0.01 0.1 1 10
Output Current [A]
Figure 17. No-audible pulse-skip waveforms Figure 18. Pulse-skip waveforms
Pulse SKIP
No Aud. SKIP
PWM
Figure 19. Power-up sequence
VCC above UVLO
Figure 20. VOUT soft-start, 1.5 V, heavy load
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Typical operating characteristics PM6675S
Figure 21. Switching section output soft-end Figure 22. LDO section output soft-end
Figure 23. -1.8 A to 1.8 A LOUT
load transient, 0.9 V
Figure 25. 0 A to 8 A VOUT
load transient, PWM
Figure 24. -1 A to 1 A LOUT
load transient, 0.9 V
Figure 26. 8 A to 0 A VOUT
load transient, PWM
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