LTC1553
5-Bit Programmable
Synchronous Switching
Regulator Controller for
Pentium
®
II Processor
FEATURES
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DESCRIPTION
The LTC
®
1553 is a high power, high efficiency switching
regulator controller optimized for 5V or 12V input to 1.8V-
3.5V output applications. It features a digitally programmable
output voltage, a precision internal reference and an internal
feedback system that provides output accuracy of
±1.5%
at
room temperature and typically
±2%
over-temperature, load
current and line voltage shifts. The LTC1553 uses a synchro-
nous switching architecture with two external N-channel
output devices, providing high efficiency and eliminating the
need for a high power, high cost P-channel device. Addition-
ally, it senses the output current across the on-resistance of
the upper N-channel FET, providing an adjustable current
limit without an external low value sense resistor.
The LTC1553 free-runs at 300kHz and can be synchronized
to a faster external clock if desired. It includes all the inputs
and outputs required to implement a power supply conform-
ing to the
Intel Pentium
®
II Processor VRM 8.2 DC/DC
Converter Specification.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
s
s
s
s
s
s
s
s
s
5-Bit Digitally Programmable 1.8V to 3.5V Fixed
Output Voltage
Provides All Features Required by the
Intel
Pentium
®
II Processor VRM 8.2 DC/DC
Converter Specification
Flags for Power Good, Over-Temperature and
Overvoltage Fault
19A Output Current Capability from a 5V or 12V Supply
Dual N-Channel MOSFET Synchronous Driver
Initial Output Accuracy:
±1.5%
Excellent Output Accuracy:
±2%
Typ Over Line,
Load and Temperature Variations
High Efficiency: Over 95% Possible
Adjustable Current Limit Without External Sense
Resistors
Fast Transient Response
Available in 20-Lead SSOP and SW Packages
APPLICATIONS
s
s
Power Supply for Pentium II, SPARC, ALPHA and
PA-RISC Microprocessors
High Power 5V or 12V to 1.8V-3.5V Regulators
TYPICAL APPLICATION
+
0.1µF
5.6k
5.6k
5.6k
V
CC
I
MAX
10µF
2.7k
PV
CC
12V
V
IN
5V
+
0.1µF
10µF
PWRGD
PENTIUM II
SYSTEM
®
PV
CC
G1
20Ω
Q1*
L
O
†
2µH
18A
C
OUT
††
330µF
×
7
V
OUT
1.8V TO
3.5V
14A
FAULT
5
OT
VID0 TO VID4
OUTEN
COMP
C1
150pF
R
C
8.2k
C
C
0.01µF
SS
SGND
GND
SENSE
LTC1553
I
FB
G2
Q2*
C
SS
0.1µF
0.1µF
*SILICONIX SUD50N03-10
**SANYO 10MV1200GX
†
COILTRONICS CTX02-13198 OR
PANASONIC 12TS-2R5SP
††
AVX TPSE337M006R0100
Figure 1. 5V to 1.8V-3.5V Supply Application
U
U
U
+
C
IN
**
1200µF
×
4
+
1553 F01
1
LTC1553
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
G2
PV
CC
GND
SGND
V
CC
SENSE
I
MAX
I
FB
SS
1
2
3
4
5
6
7
8
9
20 G1
19 OUTEN
18 VID0
17 VID1
16 VID2
15 VID3
14 VID4
13 PWRGD
12 FAULT
11 OT
Supply Voltage
V
CC
........................................................................ 9V
PV
CC
................................................................... 20V
Input Voltage
I
FB
(Note 2) ............................................ PV
CC
+ 0.3V
I
MAX
...................................................... – 0.3V to 13V
All Other Inputs ......................... – 0.3V to V
CC
+ 0.3V
Digital Output Voltage ............................... – 0.3V to 13V
I
FB
Input Current (Notes 2, 3) .......................... – 100mA
Operating Temperature Range ..................... 0°C to 70°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................. 300°C
ORDER PART
NUMBER
LTC1553CG
LTC1553CSW
COMP 10
G PACKAGE
SW PACKAGE
20-LEAD PLASTIC SSOP 20-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 100°C/ W (G)
T
JMAX
= 125°C,
θ
JA
= 100°C/ W (SW)
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC
PV
CC
V
FB
V
OUT
PARAMETER
Supply Voltage
Supply Voltage for G1, G2
Internal Feedback Voltage
1.8V Initial Output Voltage
2.8V Initial Output Voltage
3.5V Initial Output Voltage
1.8V Initial Output Voltage
2.8V Initial Output Voltage
3.5V Initial Output Voltage
Output Load Regulation
Output Line Regulation
Positive Power Good Trip Point
Negative Power Good Trip Point
FAULT Trip Point
Operating Supply Current
Shutdown Supply Current
Supply Current
Internal Oscillator Frequency
V
COMP
at Minimum Duty Cycle
V
COMP
at Maximum Duty Cycle
Error Amplifier Open-Loop DC Gain
Error Amplifier Transconductance
Error Amplifier –3dB Bandwidth
(Note 4)
CONDITIONS
V
CC
= 5V, PV
CC
= 12V, T
A
= 25°C, unless otherwise noted. (Note 3)
MIN
q
q
TYP
MAX
8
18
UNITS
V
V
V
mV
mV
mV
mV
mV
mV
mV
mV
4.5
1.265
– 27 (– 1.5%)
– 42 (– 1.5%)
– 52 (– 1.5%)
– 36 (– 2%)
– 56 (– 2%)
– 70 (– 2%)
–5
±1
With Respect to Rated Output Voltage (Figure 2)
q
q
q
27 (+ 1.5%)
42 (+ 1.5%)
52 (+ 1.5%)
36 (+ 2%)
56 (+ 2%)
70 (+ 2%)
∆V
OUT
V
PWRGD
V
FAULT
I
CC
I
PVCC
f
OSC
V
SAWL
V
SAWH
G
ERR
g
mERR
BW
ERR
I
OUT
= 0 to 14A (Note 4) (Figure 2)
V
IN
= 4.75V to 5.25V, I
OUT
= 0 (Note 4)(Figure 2)
% Above Output Voltage (Figure 2)
% Below Output Voltage (Figure 2)
% Above Output Voltage (Figure 2)
OUTEN = V
CC
= 5V (Note 5) (Figure 3)
OUTEN = 0, VID0 to VID4 Floating (Figure 3)
PV
CC
= 12V, OUTEN = V
CC
(Note 6) (Figure 3)
PV
CC
= 12V, OUTEN = 0, VID0 to VID4 Floating
(Figure 4)
(Note 4)
(Note 4)
(Note 7)
(Note 7)
COMP = Open (Note 4)
q
q
q
q
q
q
q
q
–7
12
5
–5
15
800
130
15
1
7
20
1200
250
250
300
1.8
2.8
350
40
0.9
53
1.6
400
2.3
millimho
kHz
2
U
W
U
U
W W
W
%
%
%
µA
µA
mA
µA
kHz
V
V
dB
LTC1553
ELECTRICAL CHARACTERISTICS
SYMBOL
I
IMAX
I
SS
I
SSIL
I
SSHIL
t
SSHIL
t
PWRGD
t
PWRBAD
t
FAULT
t
OT
V
OT
V
OTDD
V
SHDN
t
r
, t
f
t
NOL
DC
MAX
V
IH
V
IL
R
IN
I
SINK
PARAMETER
I
MAX
Sink Current
Soft Start Source Current
Maximum Soft Start Sink Current
Under Current Limit
Soft Start Sink Current Under Hard
Current Limit
Hard Current Limit Hold Time
Power Good Response Time↑
Power Good Response Time↓
FAULT Response Time
OT Response Time
Over-Temperature Trip Point
Over-Temperature Driver Disable
Shutdown
Driver Rise and Fall Time
Driver Nonoverlap Time
Maximum G1 Duty Cycle
VID0 to VID4 Input High Voltage
VID0 to VID4 Input Low Voltage
VID0 to VID4 Internal Pull-Up
Resistance
Digital Output Sink Current
V
IMAX
= V
CC
V
CC
= 5V, PV
CC
= 12V, T
A
= 25°C, unless otherwise noted. (Note 3)
MIN
q
q
q
q
CONDITIONS
V
SS
= 0V, V
IMAX
= 0V, V
IFB
= V
CC
V
SENSE
= V
OUT
, V
IMAX
= V
CC
, V
IFB
= 0V
(Notes 8, 9), V
SS
= V
CC
V
SENSE
= 0V, V
IMAX
= V
CC
, V
IFB
= 0V
V
SENSE
= 0V, V
IMAX
= 4V, V
IFB
↓
from 5V (Note 4)
V
SENSE
↑
from 0V to Rated V
OUT
V
SENSE
↓
from Rated V
OUT
to 0V
V
SENSE
↑
from Rated V
OUT
to V
CC
OUTEN↓, VID0 to VID4 = 0 (Note 10) (Figure 3)
OUTEN↓, VID0 to VID4 = 0 (Note 10) (Figure 3)
OUTEN↓, VID0 to VID4 = 0 (Note 10) (Figure 3)
OUTEN↓, VID0 to VID4 = 0 (Note 10) (Figure 3)
(Figure 4)
(Figure 4)
(Figure 4)
q
q
q
q
q
q
q
q
q
q
q
q
q
q
TYP
180
– 10
60
45
500
MAX
220
–7
150
UNITS
µA
µA
µA
mA
µs
150
– 13
30
20
0.5
200
200
15
1.9
1.6
1
500
500
40
2
1.7
90
2
1000
1000
60
2.12
1.8
0.8
150
88
0.8
ms
µs
µs
µs
V
V
V
ns
ns
%
V
V
kΩ
mA
30
77
2
10
10
100
84
20
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
When I
FB
is taken below GND, it will be clamped by an internal
diode. This pin can handle input currents greater than 100mA below GND
without latchup. In the positive direction, it is not clamped to V
CC
or PV
CC
.
Note 3:
All currents into device pins are positive; all currents out of the
device pins are negative. All voltages are referenced to ground unless
otherwise specified.
Note 4:
This parameter is guaranteed by correlation and is not tested
directly.
Note 5:
The LTC1553 goes into the shutdown mode if VID0 to VID4 are
floating. Due to the internal pull-up resistors, there will be an additional
0.25mA/pin if any of the VID0 to VID4 pins are pulled low.
Note 6:
Supply current in normal operation is dominated by the current
needed to charge and discharge the external FET gates. This will vary with
the LTC1553 operating frequency, supply voltage and the external FETs
used.
Note 7:
The open-loop DC gain and transconductance from the SENSE pin to
COMP pin will be (G
ERR
)(1.265/3.3) and (g
mERR
)(1.265/3.3) respectively.
Note 8:
The current limiting amplifier can sink but cannot source current.
Under normal (not current limited) operation, the output current will be zero.
Note 9:
Under typical soft current limit, the net soft start discharge current
will be 60µA (I
SSIL
) + [–10µA(I
SS
)] = 50µA. The soft start sink-to-source
current ratio is designed to be 6:1.
Note 10:
When VID0 to VID4 are all HIGH, the LTC1553 will be forced to
shut down internally. The OUTEN trip voltages are guaranteed by design for
all other input codes.
3
LTC1553
TYPICAL PERFORMANCE CHARACTERISTICS
Typical 2.8V V
OUT
Distribution
140
120
NUMBER OF UNITS
TOTAL SAMPLE SIZE = 1500
100
EFFICIENCY (%)
OUTPUT VOLTAGE (V)
80
25°C
60
40
20
0
2.775
100°C
2.785
2.815
2.795 2.805
OUTPUT VOLTAGE (V)
Line Regulation
2.825
2.820
2.815
REFER TO TYPICAL APPLICATION
CIRCUIT FIGURE 1
OUTPUT = NO LOAD
T
A
= 25°C
2.840
OUTPUT VOLTAGE (V)
OVER-TEMPERATURE TRIP POINT (V)
OUTPUT VOLTAGE (V)
2.810
2.805
2.800
2.795
2.790
2.785
2.780
2.775
4.75
4.85
5.05
5.15
4.95
INPUT VOLTAGE (V)
5.25
1553 G04
1.78
1.76
1.74
1.72
1.70
1.68
1.66
1.64
1.62
1.60
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
2.1
1.9
1.7
1.5
1.3
1.1
0.9
– 50 –25
ERROR AMPLIFIER OPEN-LOOP DC GAIN (dB)
1.80
ERROR AMPLIFIER TRANSCONDUCTANCE (millimho)
Over-Temperature Driver Disable
vs Temperature
OVER-TEMPERATURE DRIVER DISABLE (V)
4
U W
1553 G01
1553 G07
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
2.825
Load Regulation
2.825
REFER TO TYPICAL APPLICATION
2.820 CIRCUIT FIGURE 1
V = 5V, PV
CC
= 12V, T
A
= 25°C
2.815
IN
2.810
2.805
2.800
2.795
2.790
2.785
2.780
2.775
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
OUTPUT CURRENT (A)
1533 G03
A
B
REFER TO TYPICAL APPLICATION
CIRCUIT FIGURE 1
V
IN
= 5V, PV
CC
= 12V, V
OUT
= 2.8V,
C
OUT
= 330µF
×
7, L
O
= 2µH
A: Q1 = 1
×
SUD50N03-10
Q2 = 1
×
SUD50N03-10
B: Q1 = 2
×
SUD50N03-10
Q2 = 1
×
SUD50N03-10
NO FAN
Q1 IS MOUNTED ON 1IN
2
COPPER AREA
0
0.3
2
4
6
8
10
LOAD CURRENT (A)
12
14
1533 G02
Output Temperature Drift
2.860
2.850
2.830
2.820
2.810
2.800
2.790
2.780
2.770
2.660
2.750
2.740
– 50 – 25
50
0
75
25
TEMPERATURE (°C)
100
125
2.12
2.10
2.08
2.06
2.04
2.02
2.00
1.98
1.96
1.94
1.92
Over-Temperature Trip Point
vs Temperature
1.90
– 50 – 25
50
0
75
25
TEMPERATURE (°C)
100
125
1553 G05
1553 G06
Error Amplifier Transconductance
vs Temperature
2.3
60
Error Amplifier Open-Loop
DC Gain vs Temperature
55
50
45
50
25
75
0
TEMPERATURE (°C)
100
125
40
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
1553 G08
1553 G09
LTC1553
TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency
vs Temperature
350
340
OSCILLATOR FREQUENCY (kHz)
210
I
MAX
SINK CURRENT (µA)
200
190
180
170
160
150
–50
SOFT START SOURCE CURRENT (µA)
–25
75
0
50
25
TEMPERATURE (°C)
100
125
330
320
310
300
290
280
270
260
250
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
Maximum G1 Duty Cycle
vs Temperature
92
MAXIMUM G1 DUTY CYCLE (%)
90
88
G1, G2 CAPACITANCE = 1100pF
86
84
82
80
78
– 50 – 25
50
25
75
0
TEMPERATURE (°C)
100
125
5500pF
7700pF
2200pF
3300pF
V
CC
OPERATING SUPPLY CURRENT (mA)
OSCILLATOR FREQUENCY = 300kHz
1.2
1.1
1.0
0.9
0.8
0.7
0.6
V
CC
SHUTDOWN SUPPLY CURRENT (mA)
PV
CC
Supply Current
vs Gate Capacitance
70
60
PV
CC
SUPPLY CURRENT (mA)
50
40
30
20
10
0
0
2000
6000
GATE CAPACITANCE (pF)
4000
8000
1553 G16
PV
CC
= 12V
T
A
= 25°C
OUTPUT VOLTAGE (V)
U W
1553 G10
I
MAX
Sink Current
vs Temperature
220
Soft Start Source Current
vs Temperature
–7
–8
–9
–10
–11
–12
–13
– 50 – 25
50
25
75
0
TEMPERATURE (°C)
100
125
1553 G11
1553 G12
V
CC
Operating Supply Current
vs Temperature
250
V
CC
= 5V
f
OSC
= 300kHz
225
200
175
150
125
100
75
V
CC
Shutdown Supply Current
vs Temperature
0.5
– 50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
50
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
1553 G13
1553 G14
1553 G15
Output Over Current Protection
3.0
2.5
2.0
1.5
Q1 CASE = 90°C, V
OUT
= 2.8V
Q1 = 2
×
MTD20N03HDL
Q2 = 1
×
MTD20N03HDL
R
IMAX
= 2.7k, R
IFB
= 20Ω,
SS CAP = 0.01µF
Transient Response
50mV/DIV
5A/DIV
1.0
SHORT-CIRCUIT
CURRENT
0.5
0
0
2
4
6
8 10 12 14
OUTPUT CURRENT (A)
16
18
1553 G18
100µs/DIV
1553 G17
5
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