LTC1909-8
Wide Operating Range,
No R
SENSE
TM
Step-Down DC/DC
Controller with SMBus Programming
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
s
s
s
s
s
s
SMBus/I
2
C
TM
Programmable Output Voltage:
1.3V to 3.5V
No Sense Resistor Required
2% to 90% Duty Cycle at 200kHz
t
ON(MIN)
≤
100ns
True Current Mode Control
Stable with Ceramic C
OUT
Power Good Output Voltage Monitor and 50µs Timer
Wide V
IN
Range: 4V to 36V (Abs Max)
Precision Resistor Divider and Reference Provide
±1.35%
Output Voltage Accuracy Over Temperature
Adjustable Switching Frequency and Current Limit
Forced Continuous Control Pin
Programmable Soft-Start
Output Overvoltage Protection
Optional Short-Circuit Shutdown Timer
Available in a 28-Lead SSOP Package
The LTC
®
1909-8 is a synchronous step-down switching
regulator controller with a digitally programmable output
voltage. The output voltage is selected from one of two
5-bit settings programmed into internal registers via a
2-wire SMBus/I
2
C interface. The interface features safe-
guards against invalid output voltages and allows the mi-
croprocessor to turn the regulator on and off. Valley cur-
rent control delivers very low duty cycles without requiring
a sense resistor. Operating frequency is selected by an
external resistor and is compensated for variations in V
IN
and V
OUT
.
Discontinuous mode operation provides high efficiency
operation at light loads. A forced continuous control pin
reduces noise and RF interference and can assist second-
ary winding regulation by disabling discontinuous mode
operation when the main output is lightly loaded.
Fault protection is provided by internal foldback current
limiting, an output overvoltage comparator and optional
short-circuit shutdown timer.
The LTC1909-8 is available in the 28-lead SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation.
I
2
C is a trademark of Philips Electronics N.V.
APPLICATIO S
s
s
Power Supplies for DSPs, ASICs, FPGAs and CPUs
Voltage Margining
TYPICAL APPLICATIO
100k
100k
11k
100k
0.1µF
LTC1909-8
1
2
39k
3
4
100pF
5
6
470pF
7
20k
8
9
SEL
SDA
SCL
VRON
10
11
12
13
14
RUN/SS
V
ON
PGOOD
V
RNG
FCB
I
TH
SGND
I
ON
V
FB
SEL
SDA
SCL
VRON
PGTMR
BOOST
TG
SW
SENSE
+
PGND
BG
INTV
CC
V
IN
28
27
26
25
24
23
22
21
1Ω
0.1µF
R
ON
1.4M 1%
M2
0.22µF
M1
L1
1.8µH
CMDSH-3
+
20 5V
EXTV
CC
EXT
19
V
CC
18
GND
17
FB
16
V
OSENSE
15
CPUON
4.7µF
6.3V
Figure 1. High Efficiency Step-Down Converter
19098f
U
C
IN
10µF
50V
×4
V
IN
5V TO 24V
GND
V
OUT
2.5V OR 2.6V
10A
(V
OUT
SET BY SEL)
U
U
+
D1
C
OUT1, 2
180µF
4V
×2
C
OUT3
22µF
6.3V
X7R
GND
C
IN
: UNITED CHEMICON THCR60E1H106TZ
C
OUT1, 2
: CORNELL DUBILIER ESRE181ME04B/
PANASONIC EEFVEOG181R
D1: DIODES INC. B340A
L1: SUMIDA CEP125-1R8MC-H
M1: Si4884
M2: Si4874
19098 F01
1
LTC1909-8
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS
V
ON
PGOOD
V
RNG
FCB
I
TH
SGND
I
ON
V
FB
1
2
3
4
5
6
7
8
9
28 BOOST
27 TG
26 SW
25 SENSE
+
24 PGND
23 BG
22 INTV
CC
21 V
IN
20 EXTV
CC
19 V
CC
18 GND
17 FB
16 V
OSENSE
15 CPUON
Input Supply Voltage
V
IN
, I
ON
..................................................– 0.3V to 36V
Boosted Topside Driver Supply Voltage
BOOST .................................................. – 0.3V to 42V
SW, SENSE
+
Voltages ................................. – 5V to 36V
EXTV
CC
, (BOOST – SW), RUN/SS, PGOOD, INTV
CC
,
SEL, SDA, SCL, VRON, PGTMR, V
OSENSE
,
FB, CPUON, V
CC
Voltages .......................... – 0.3V to 7V
FCB, V
ON
, V
RNG
Voltages ....... – 0.3V to (INTV
CC
+ 0.3V)
I
TH
, V
FB
Voltages...................................... – 0.3V to 2.7V
TG, BG, INTV
CC
, EXTV
CC
Peak Currents .................... 2A
TG, BG, INTV
CC
, EXTV
CC
RMS Currents .............. 50mA
Operating Ambient Temperature Range
LTC1909-8EG (Note 2) ....................... – 40°C to 85°C
Junction Temperature (Note 4) ............................ 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1909-8EG
SEL 10
SDA 11
SCL 12
VRON 13
PGTMR 14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
PARAMETER
Input DC Supply Current
Normal
Shutdown Supply Current
Feedback Reference Voltage
Feedback Voltage Line Regulation
Feedback Voltage Load Regulation
Feedback Input Current
Error Amplifier Transconductance
Forced Continuous Threshold
Forced Continuous Pin Current
On-Time
Minimum On-Time
Minimum Off-Time
Maximum Current Sense Threshold
V
PGND
– V
SENSE+
Minimum Current Sense Threshold
V
PGND
– V
SENSE+
Output Overvoltage Fault Threshold
Main Control Loop
(Switching Regulator Controller) The
q
denotes specifications which apply
over the full operating temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
900
15
I
TH
= 1.2V (Note 3)
V
IN
= 4V to 30V, I
TH
= 1.2V (Note 3)
I
TH
= 0.5V to 1.9V (Note 3)
V
FB
= 0.8V
I
TH
= 1.2V (Note 3)
V
FCB
= 0.8V
I
ON
= 60µA, V
ON
= 1.5V
I
ON
= 30µA, V
ON
= 1.5V
I
ON
= 180µA, V
ON
= 0V
I
ON
= 60µA, V
ON
= 1.5V
V
RNG
= 1V, V
FB
= 0.76V
V
RNG
= 0V, V
FB
= 0.76V
V
RNG
= INTV
CC
, V
FB
= 0.76V
V
RNG
= 1V, V
FB
= 0.84V
V
RNG
= 0V, V
FB
= 0.84V
V
RNG
= INTV
CC
, V
FB
= 0.84V
5.5
q
q
q
q
q
2000
30
0.808
– 0.3
±50
2
0.84
–2
288
575
100
400
153
107
214
V
FB
∆V
FB(LINEREG)
∆V
FB(LOADREG)
I
FB
g
m(EA)
V
FCB
I
FCB
t
ON
t
ON(MIN)
t
OFF(MIN)
V
SENSE(MAX)
0.792
0.800
0.002
– 0.05
–5
1.4
0.76
212
425
1.7
0.8
–1
250
500
50
250
113
79
158
133
93
186
– 67
– 47
– 93
7.5
V
SENSE(MIN)
∆V
FB(OV)
9.5
2
U
µA
µA
V
%/V
%
nA
mS
V
µA
ns
ns
ns
ns
mV
mV
mV
mV
mV
mV
%
19098f
W
U
U
W W
W
LTC1909-8
ELECTRICAL CHARACTERISTICS
SYMBOL
∆V
FB(UV)
V
RUN/SS(ON)
V
RUN/SS(LE)
V
RUN/SS(LT)
I
RUN/SS(C)
I
RUN/SS(D)
V
IN(UVLO)
V
IN(UVLOR)
TG R
UP
TG R
DOWN
BG R
UP
BG R
DOWN
TG t
r
TG t
f
BG t
r
BG t
f
V
INTVCC
∆V
LDO(LOADREG)
V
EXTVCC
∆V
EXTVCC
∆V
EXTVCC(HYS)
PGOOD Output
∆V
FBH
∆V
FBL
∆V
FB(HYS)
V
PGL
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Low Voltage
PARAMETER
Output Undervoltage Fault Threshold
RUN Pin Start Threshold
RUN Pin Latchoff Enable Threshold
RUN Pin Latchoff Threshold
Soft-Start Charge Current
Soft-Start Discharge Current
Undervoltage Lockout
Undervoltage Lockout Release
TG Driver Pull-Up On Resistance
TG Driver Pull-Down On Resistance
BG Driver Pull-Up On Resistance
BG Driver Pull-Down On Resistance
TG Rise Time
TG Fall Time
BG Rise Time
BG Fall Time
Internal V
CC
Voltage
Internal V
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Switch Drop Voltage
EXTV
CC
Switchover Hysteresis
(Switching Regulator Controller) The
q
denotes specifications which apply
over the full operating temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V unless otherwise noted.
CONDITIONS
q
MIN
520
0.8
TYP
600
1.5
4
3.5
MAX
680
2
4.5
4.2
–3
3
3.9
4
3
3
4
2
UNITS
mV
V
V
V
µA
µA
V
V
Ω
Ω
Ω
Ω
ns
ns
ns
ns
RUN/SS Pin Rising
RUN/SS Pin Falling
V
RUN/SS
= 0V
V
RUN/SS
= 4.5V, V
FB
= 0V
V
IN
Falling
V
IN
Rising
TG High
TG Low
BG High
BG Low
C
LOAD
= 3300pF, 20% to 80% of Swing
C
LOAD
= 3300pF, 20% to 80% of Swing
C
LOAD
= 3300pF, 20% to 80% of Swing
C
LOAD
= 3300pF, 20% to 80% of Swing
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
CC
= 0mA to 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
Rising
I
CC
= 20mA, V
EXTVCC
= 5V
q
q
q
q
– 0.5
0.8
– 1.2
1.8
3.4
3.5
2
2
3
1
20
20
20
20
Internal V
CC
Regulator
4.7
4.5
5
– 0.1
4.7
150
200
V
FB
Rising
V
FB
Falling
V
FB
Returning
I
PGOOD
= 5mA
5.5
– 5.5
7.5
– 7.5
1
0.15
9.5
– 9.5
2
0.4
300
5.3
±2
V
%
V
mV
mV
%
%
%
V
(SMBus VID Programmer) The
q
denotes the specifications which apply over the full operating temperature range, otherwise
specifications are at T
A
= 25°C. 2.7V
≤
V
CC
≤
5.5V (Note 5) unless otherwise stated.
SYMBOL
V
CC
I
CC
R
FB-SENSE
DE
V
IH
V
IL
V
IH
V
IL
V
HYST
V
OL
I
IN
PARAMETER
Operating Supply Voltage Range
Supply Current
Resistance Between V
OSENSE
and FB
Divider Error (Note 6)
SCL, SDA Input High Voltage
SCL, SDA Input Low Voltage
SEL, VRON Input High Voltage
SEL, VRON Input Low Voltage
SEL, VRON Hysteresis
SDA, CPUON PGTMR Output Low Voltage I = 3mA
SCL, SDA, SEL, VRON Input Current
SDA Not Acknowledging, 0
≤
V
PIN
≤
5.5V,
V
PIN
= 5.5V for VRON only
q
q
q
CONDITIONS
CPUON, PGTMR Pins Are Open
V
OSENSE
Programmed from 1.3V to 3.5V
q
q
q
q
q
MIN
2.7
14
– 0.35
2.1
TYP
MAX
5.5
350
UNITS
V
µA
kΩ
%
V
V
V
V
mV
20
26
0.35
0.8
1.3
0.8
1.3
±50
2
0.4
±10
V
µA
19098f
3
LTC1909-8
ELECTRICAL CHARACTERISTICS
(SMBus VID Programmer) The
q
denotes the specifications which apply over the full operating temperature range, otherwise
specifications are at T
A
= 25°C. 2.7V
≤
V
CC
≤
5.5V (Note 5) unless otherwise stated.
SYMBOL
I
SK1
I
SK2
I
LKG
I
PU
f
SMB
t
BUF
t
HD:STA
t
SU:STA
t
SU:STO
t
HD:DAT
t
SU:DAT
t
LOW
t
HIGH
t
f
t
r
t
SSH
t
SSL
t
SPL
t
PH
t
PL
t
PPL
t
VH
t
VL
t
VPL
t
PGL
PARAMETER
SDA, PGTMR, CPUON
Sink Current at V
CC
= 2.7V
SDA, PGTMR, CPUON
Sink Current at V
CC
= 5.5V
PGTMR, CPUON Leakage Current
VRON Pull-Up Current
SMBus Operating Frequency
Bus Free Time Between Stop/Start
Hold Time After (Repeated) Start
Repeated Start Setup Time
Stop Condition Setup Time
Data Hold Time
Data Setup Time
Clock Low Period
Clock High Period
SCL, SDA Fall Time
SCL, SDA Rise Time
SEL to V
OSENSE
High (Note 8)
SEL to V
OSENSE
Low (Note 8)
SEL Toggling to PGTMR Low
Stop Bit to CPUON High (Note 9)
Stop Bit to CPUON Low (Note 9)
Stop Bit to PGTMR Low (Note 9)
VRON High to CPUON High
VRON Low to CPUON Low
VRON Low to PGTMR Low
PGTMR Low Duration
0.9V
CC
to 0.65V
0.65V to 2.25V
Toggle SEL to Switch from 01111B to 10000B,
V
FB
= 0.8V
Toggle SEL to Switch from 10000B to 01111B,
V
FB
= 0.8V
Toggle SEL to Select New Code
C
L
= 100pF, 10kΩ Pull-Up, S2 in Test Circuit
C
L
= 100pF, 10kΩ Pull-Up, S2 in Test Circuit
C
L
= 0.1µF, 10kΩ Pull-Up, S1 in Test Circuit
C
L
= 100pF, 10kΩ Pull-Up, S2 in Test Circuit
C
L
= 100pF, 10kΩ Pull-Up, S2 in Test Circuit
C
L
= 0.1µF, 10kΩ Pull-Up, S1 in Test Circuit
C
L
= 100pF, 10kΩ Pull-Up, S2 in Test Circuit
C
L
= 100pF, 10kΩ Pull-Up, S2 in Test Circuit
CONDITIONS
0
≤
V
PIN
≤
2.7V
0
≤
V
PIN
≤
5.5V
0
≤
V
PIN
≤
5.5V
V
PIN
= 0
q
q
q
MIN
5
35
TYP
19
65
MAX
60
150
±0.2
UNITS
mA
mA
µA
µA
KHz
µs
µs
µs
µs
ns
ns
µs
µs
–1
10
4.7
4
4.7
4
300
250
4.7
4
– 2.5
–7
100
Timing (Note 7)
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
300
1000
500
500
160
500
2
20
50
250
2
50
130
30
50
500
70
ns
ns
ns
ns
ns
µs
µs
ns
µs
µs
ns
µs
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1909-8E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
The LTC1909-8 is tested in a feedback loop that adjusts V
FB
to
achieve a specified error amplifier output voltage (I
TH
).
Note 4:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
as follows:
LTC1909-8E: T
J
= T
A
+ (P
D
• 130°C/W)
Note 5:
All currents into device pins are positive; all currents out of device pins
are negative. All voltages are referenced to device ground unless otherwise
noted.
Note 6:
The divider error is tested in a feedback loop that adjusts FB to
0.8V for each 5-bit code.
Note 7:
These parameters are guaranteed by design and are not tested in
production. SMBus timing is referenced to V
IL
and V
IH
levels.
Note 8:
Dominated by the switching regulator. The delay due to the SMBus
VID programmer is only 500ns typ.
Note 9:
Measured from the rising edge of SDA during Data High
acknowledgment.
19098f
4
LTC1909-8
TYPICAL PERFOR A CE CHARACTERISTICS
Transient Response
Transient Response
(Discontinuous Mode)
100
V
OUT
50mV/DIV
V
OUT
50mV/DIV
EFFICIENCY (%)
I
L
5A/DIV
20µs
LOAD STEP 0A TO 10A
V
IN
= 15V
V
OUT
= 2.5V
FCB = 0V
FIGURE 1 CIRCUIT
Efficiency vs Input Voltage
100
FCB = 5V
FIGURE 1 CIRCUIT
300
95
I
LOAD
= 1A
90
I
LOAD
= 10A
85
FREQUENCY (kHz)
EFFICIENCY (%)
260
∆V
OUT
(%)
80
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
19098 G19
I
TH
Voltage vs Load Current
2.5
FIGURE 1 CIRCUIT
V
RNG
= 2V
1.4V
1V
MAXIMUM CURRENT SENSE THRESHOLD (mV)
CURRENT SENSE THRESHOLD (mV)
2.0
I
TH
VOLTAGE (V)
1.5
CONTINUOUS
MODE
1.0
DISCONTINUOUS
MODE
0.5
0
0
10
5
LOAD CURRENT (A)
U W
15
19098 G22
Efficiency vs Load Current
90
DISCONTINUOUS
MODE
80
CONTINUOUS
MODE
70
V
IN
= 10V
V
OUT
= 2.5V
EXTV
CC
= 5V
FIGURE 1 CIRCUIT
0.1
0.01
1
LOAD CURRENT (A)
10
19098 G18
I
L
5A/DIV
19098 G16
20µs
LOAD STEP 1A TO 10A
V
IN
= 15V
V
OUT
= 2.5V
FCB = INTV
CC
FIGURE 1 CIRCUIT
60
19098 G17
50
0.001
Frequency vs Input Voltage
FCB = 0V
FIGURE 1 CIRCUIT
I
OUT
= 10A
0
Load Regulation
FIGURE 1 CIRCUIT
280
–0.1
–0.2
240
I
OUT
= 0A
–0.3
220
200
5
10
15
INPUT VOLTAGE (V)
20
–0.4
25
19098 G20
0
2
6
4
LOAD CURRENT (A)
8
10
19098 G21
Current Sense Threshold
vs I
TH
Voltage
300
150
125
100
75
50
25
0
Current Limit Foldback
200
100
0.7V
0.5V
0
–100
–200
0
0.5
1.0
1.5
2.0
I
TH
VOLTAGE (V)
2.5
3.0
0
0.2
0.4
V
FB
(V)
0.6
0.8
1778 G09
19098 G23
19098f
5
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