LTC1929/LTC1929-PG
2-Phase, High Efficiency,
Synchronous Step-Down
Switching Regulators
FEATURES
s
s
DESCRIPTIO
s
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s
s
s
s
s
s
s
s
s
s
s
2-Phase Single Output Controller
Reduces Required Input Capacitance and Power
Supply Induced Noise
Current Mode Control Ensures Current Sharing
Phase-Lockable Fixed Frequency: 150kHz to 300kHz
True Remote Sensing Differential Amplifier
OPTI-LOOP
TM
Compensation Improves Transient
Response
±
1% Output Voltage Accuracy
Power Good Output Voltage Monitor (LTC1929-PG)
Wide V
IN
Range: 4V to 36V Operation
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Soft-Start Current Ramping
Internal Current Foldback
Short-Circuit Shutdown Timer with Defeat Option
Overvoltage Soft-Latch Eliminates Nuisance Trips
Available in 28-Lead SSOP Package
The LTC
®
1929/LTC1929-PG are 2-phase, single output,
synchronous step-down current mode switching regula-
tor controllers that drive N-channel external power MOSFET
stages in a phase-lockable fixed frequency architecture.
The 2-phase controllers drive their two output stages out
of phase at frequencies up to 300kHz to minimize the RMS
ripple currents in both input and output capacitors. The
2-phase technique effectively multiplies the fundamental
frequency by two, improving transient response while
operating each channel at an optimum frequency for
efficiency. Thermal design is also simplified.
An internal differential amplifier provides true remote
sensing of the regulated supply’s positive and negative
output terminals as required by high current applications.
The RUN/SS pin provides soft-start and a defeatable,
timed, latched short-circuit shutdown to shut down both
channels. Internal foldback current limit provides protec-
tion for the external synchronous MOSFETs in the event of
an output fault. OPTI-LOOP compensation allows the
transient response to be optimized over a wide range of
output capacitance and ESR values.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
APPLICATIO S
s
s
s
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Desktop Computers
Internet/Network Servers
Large Memory Arrays
DC Power Distribution Systems
TYPICAL APPLICATIO
0.1µF
V
IN
0.1µF
10Ω
10µF
35V
CERAMIC
×4
0.47µF
D1
L1
1µH
0.002Ω
TG1
BOOST1
LTC1929 SW1
RUN/SS
BG1
PGND
I
TH
SENSE1
+
SENSE1
–
TG2
SGND
BOOST2
SW2
V
DIFFOUT
EAIN
BG2
1000pF
10k
100pF
0.47µF
D2
10µF
L2
1µH
0.002Ω
16k
+
INTV
CC
SENSE2
+
SENSE2
–
16k
V
OS –
V
OS +
C
OUT
: T510E108K004AS L1, L2: CEPH149-1ROMC
Figure 1. High Current 2-Phase Step-Down Converter
U
V
IN
5V TO 28V
V
OUT
1.6V/40A
U
U
+
C
OUT
1000µF
4V
×2
1929 F01
1
LTC1929/LTC1929-PG
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS
SENSE1
+
SENSE1
–
EAIN
PLLFLTR
PLLIN
NC
I
TH
SGND
1
2
3
4
5
6
7
8
9
28 NC
27 TG1
26 SW1
25 BOOST1
24 V
IN
23 BG1
22 EXTV
CC
21 INTV
CC
20 PGND
19 BG2
18 BOOST2
17 SW2
16 TG2
15 AMPMD*
Input Supply Voltage (V
IN
).........................36V to – 0.3V
Topside Driver Voltages (BOOST1,2) .........42V to – 0.3V
Switch Voltage (SW1, 2) .............................36V to – 5 V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages ........................ (1.1)INTV
CC
to – 0.3V
EAIN, V
OS+
, V
OS–
, EXTV
CC
, INTV
CC
,
RUN/SS, AMPMD Voltages ..........................7V to – 0.3V
Boosted Driver Voltage (BOOST-SW) ..........7V to – 0.3V
PLLFLTR, PLLIN, V
DIFFOUT
Voltages .... INTV
CC
to – 0.3V
I
TH
Voltage ................................................2.7V to – 0.3V
Peak Output Current <1µs(TGL1,2, BG1,2) ................ 3A
INTV
CC
RMS Output Current ................................ 50mA
Operating Ambient Temperature Range
LTC1929C .................................................. 0°C to 85°C
LTC1929I .............................................. – 40°C to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1929CG
LTC1929CG-PG
LTC1929IG
LTC1929IG-PG
V
DIFFOUT
10
V
OS –
11
V
OS +
12
SENSE2
–
13
SENSE2
+
14
G PACKAGE
28-LEAD PLASTIC SSOP
*PGOOD ON LTC1929-PG
T
JMAX
= 125°C,
θ
JA
= 95°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
EAIN
V
SENSEMAX
I
INEAIN
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Maximum Current Sense Threshold
Feedback Current
Output Voltage Load Regulation
Main Control Loop
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
(Note 3); I
TH
Voltage = 1.2V
V
SENSE –
= 5V
V
SENSE1, 2
= 5V, LTC1929 Only
(Note 3)
(Note 3)
Measured in Servo Loop; I
TH
Voltage = 0.7V
Measured in Servo Loop; I
TH
Voltage = 2V
V
IN
= 3.6V to 30V (Note 3)
Measured at V
EAIN
V
IN
Ramping Down
I
TH
= 1.2V; Sink/Source 5µA; (Note 3)
I
TH
= 1.2V; (g
m
xZ
L
; No Ext Load); (Note 3)
(Note 4)
EXTV
CC
Tied to V
OUT
; V
OUT
= 5V
V
RUN/SS
= 0V
V
RUN/SS
= 1.9V
V
RUN/SS
Rising
V
RUN/SS
Rising from 3V
– 0.5
1.0
0.84
3
q
q
q
q
MIN
0.792
62
65
TYP
0.800
75
75
–5
0.05
– 0.1
0.002
0.86
3.5
3
1.5
470
20
–1.2
1.5
4.1
MAX
0.808
88
85
– 50
0.5
– 0.5
0.02
0.88
4
UNITS
V
mV
mV
nA
%
%
%/V
V
V
mmho
V/mV
µA
µA
µA
V
V
V
REFLNREG
V
OVL
UVLO
g
m
g
mOL
I
Q
Reference Voltage Line Regulation
Output Overvoltage Threshold
Undervoltage Lockout
Transconductance Amplifier g
m
Transconductance Amplifier Gain
Input DC Supply Current
Normal Mode
Shutdown
Soft-Start Charge Current
RUN/SS Pin ON Threshold
RUN/SS Pin Latchoff Arming
40
1.9
4.5
I
RUN/SS
V
RUN/SS
V
RUN/SSLO
2
U
W
U
U
W W
W
LTC1929/LTC1929-PG
ELECTRICAL CHARACTERISTICS
SYMBOL
I
SCL
I
SDLHO
I
SENSE
DF
MAX
TG1, 2 t
r
TG1, 2 t
f
BG1, 2 t
r
BG1, 2 t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCC
V
LDO
INT
V
LDO
EXT
V
LDO
EXT-PG
V
EXTVCC
V
LDOHYS
f
NOM
f
LOW
f
HIGH
R
PLLIN
I
PLLFLTR
PARAMETER
RUN/SS Discharge Current
Shutdown Latch Disable Current
Total Sense Pins Source Current
Maximum Duty Factor
Top Gate Transition Time:
Rise Time
Fall Time
Bottom Gate Transition Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Voltage Drop
EXTV
CC
Voltage Drop
EXTV
CC
Switchover Voltage
EXTV
CC
Switchover Hysteresis
Nominal Frequency
Lowest Frequency
Highest Frequency
PLLIN Input Resistance
Phase Detector Output Current
Sinking Capability
Sourcing Capability
Controller 2-Controller 1 Phase
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
EAIN
with Respect to Set Output Voltage
V
EAIN
Ramping Negative
V
EAIN
Ramping Positive
Differential Amp Mode
Differential Amp Mode; 0V < V
CM
< 5V
Differential Amp Mode; Measured at V
OS
+ Input
Op Amp Mode; V
CM
= 2.5V; V
DIFFOUT
= 5V;
I
DIFFOUT
= 1mA (LTC1929 Only)
–6
6
0.995
46
–7.5
7.5
1
55
80
6
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
Soft Short Condition V
EAIN
= 0.5V;
V
RUN/SS
= 4.5V
V
EAIN
= 0.5V
Each Channel: V
SENSE1
–
, 2
– = V
SENSE1
+
, 2
+ = 0V
In Dropout
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
Tested with a Square Wave (Note 6)
6V < V
IN
< 30V; V
EXTVCC
= 4V
I
CC
= 0 to 20mA; V
EXTVCC
= 4V
I
CC
= 20mA; V
EXTVCC
= 5V
I
CC
= 20mA, V
EXTVCC
= 5V, LTC1929-PG
I
CC
= 20mA, EXTV
CC
Ramping Positive
I
CC
= 20mA, EXTV
CC
Ramping Negative
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥
2.4V
190
120
280
q
MIN
0.5
TYP
2.0
1.6
MAX
4.0
5
UNITS
µA
µA
µA
%
– 85
98
– 60
99.5
30
40
30
20
90
90
180
90
90
90
90
ns
ns
ns
ns
ns
ns
ns
Internal V
CC
Regulator
4.8
5.0
0.2
120
80
4.5
4.7
0.2
220
140
310
50
– 15
15
180
0.1
0.3
±1
– 9.5
9.5
1.005
250
160
360
5.2
1.0
240
160
V
%
mV
mV
V
V
kHz
kHz
kHz
kΩ
µA
µA
Deg
V
µA
%
%
V/V
dB
kΩ
mV
Oscillator and Phase-Locked Loop
R
RELPHS
V
PGL
I
PGOOD
V
PG
PGOOD Output (LTC1929-PG Only)
Differential Amplifier/Op Amp Gain Block (Note 5)
A
DA
CMRR
DA
R
IN
V
OS
Gain
Common Mode Rejection Ratio
Input Resistance
Input Offset Voltage
3
LTC1929/LTC1929-PG
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
PARAMETER
Input Bias Current
Open Loop DC Gain
Common Mode Input Voltage Range
Common Mode Rejection Ratio
Power Supply Rejection Ratio
Maximum Output Current
Maximum Output Voltage
Gain-Bandwidth Product
Slew Rate
CONDITIONS
Op Amp Mode (LTC1929 Only)
Op Amp Mode; 0.7V
≤
V
DIFFOUT
< 10V
(LTC1929 Only)
Op Amp Mode (LTC1929 Only)
Op Amp Mode; 0V < V
CM
< 3V (LTC1929 Only)
Op Amp Mode; 6V < V
IN
< 30V (LTC1929 Only)
Op Amp Mode; V
DIFFOUT
= 0V (LTC1929 Only)
Op Amp Mode; I
DIFFOUT
= 1mA (LTC1929 Only)
Op Amp Mode; I
DIFFOUT
= 1mA (LTC1929 Only)
Op Amp Mode; R
L
= 2k (LTC1929 Only)
0
70
70
10
10
90
90
35
11
2
5
MIN
SYMBOL
I
B
A
OL
V
CM
CMRR
OA
PSRR
OA
I
CL
V
O(MAX)
GBW
SR
TYP
30
5000
3
MAX
200
UNITS
nA
V/mV
V
dB
dB
mA
V
MHz
V/µs
Note 1:
Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1929CG: T
J
= T
A
+ (P
D
• 95°C/W)
Note 3:
The LTC1929 is tested in a feedback loop that servos V
ITH
to a
specified voltage and measures the resultant V
EAIN
.
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 5:
When the AMPMD pin is high (default for the LTC1929-PG), the
LTC1929 IC pins are connected directly to the internal op amp inputs.
When the AMPMD pin is low, internal MOSFET switches connect four
40k resistors around the op amp to create a standard unity-gain
differential amp.
Note 6:
Minimum on-time condition corresponds to the on inductor
peak-to-peak ripple current
≥
40% of I
MAX
(see minimum on-time
considerations in the Applications Information section).
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Output Current
(Figure 13)
100
100
V
EXTVCC
= 5V
80
V
IN
= 5V
80
90
V
EXTVCC
= 0V
60
EFFICIENCY (%)
EFFICIENCY (%)
60
V
IN
= 8V
V
IN
= 12V
V
IN
= 20V
EFFICIENCY (%)
40
20
0
0.1
V
OUT
= 2V
V
EXTVCC
= 0V
FREQ = 200kHz
1
10
OUTPUT CURRENT (A)
100
1929 G01
4
U W
Efficiency vs Output Current
(Figure 13)
100
Efficiency vs V
IN
(Figure 13)
V
EXTVCC
= 5V
I
OUT
= 20A
V
OUT
= 2V
V
OUT
= 1.6V
80
40
70
20
V
IN
= 12V
V
OUT
= 2V
FREQ = 200kHz
1
10
OUTPUT CURRENT (A)
100
1929 G02
60
0
0.1
50
5
10
V
IN
(V)
1929 G03
15
20
LTC1929/LTC1929-PG
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode
1000
V
OUT
= 5V
V
EXTVCC
= V
OUT
250
INTV
CC
AND EXTV
CC
SWITCH VOLTAGE (V)
EXTV
CC
VOLTAGE DROP (mV)
800
SUPPLY CURRENT (µA)
600
ON
400
200
SHUTDOWN
0
0
5
20
15
10
25
INPUT VOLTAGE (V)
30
35
Internal 5V LDO Line Reg
5.1
5.0
75
I
LOAD
= 1mA
INTV
CC
VOLTAGE (V)
4.9
V
SENSE
(mV)
4.8
4.7
4.6
4.5
4.4
0
5
20
15
25
10
INPUT VOLTAGE (V)
30
35
1929 G07
V
SENSE
(mV)
Maximum Current Sense Threshold
vs V
RUN/SS
(Soft-Start)
80
V
SENSE(CM)
= 1.6V
60
V
SENSE
(mV)
V
SENSE
(mV)
72
V
SENSE
(mV)
40
20
0
0
1
2
3
V
RUN/SS
(V)
1929 G10
4
U W
1929 G04
EXTV
CC
Voltage Drop
5.05
5.00
4.95
4.90
4.85
4.80
4.75
INTV
CC
and EXTV
CC
Switch
Voltage vs Temperature
INTV
CC
VOLTAGE
200
LTC1929
150
LTC1929-PG
100
50
EXTV
CC
SWITCHOVER THRESHOLD
0
0
10
30
20
CURRENT (mA)
40
50
1929 G05
4.70
– 50 – 25
50
25
75
0
TEMPERATURE (°C)
100
125
1929 G06
Maximum Current Sense Threshold
vs Duty Factor
80
70
60
50
Maximum Current Sense Threshold
vs Percent on Nominal Output
Voltage (Foldback)
50
40
30
20
10
25
0
0
20
40
60
DUTY FACTOR (%)
80
100
1929 G08
0
50
100
0
25
75
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
1929 G09
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
80
90
80
70
60
50
40
30
20
10
0
Current Sense Threshold
vs I
TH
Voltage
76
68
64
–10
–20
–30
5
6
60
0
1
3
4
2
COMMON MODE VOLTAGE (V)
5
1929 G11
0
0.5
1
1.5
V
ITH
(V)
2
2.5
1929 G12
5
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