MAX1845.pdf

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323064355 UNPDF
19-1955; Rev 2; 1/03
Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
General Description
The MAX1845 is a dual PWM controller configured for
step-down (buck) topologies that provides high efficien-
cy, excellent transient response, and high DC output
accuracy necessary for stepping down high-voltage bat-
teries to generate low-voltage chipset and RAM power
supplies in notebook computers. The CS_ inputs can be
used with low-side sense resistors to provide accurate
current limits or can be connected to LX_, using low-side
MOSFETs as current-sense elements.
The on-demand PWM controllers are free running, con-
stant on-time with input feed-forward. This configuration
provides ultra-fast transient response, wide input-output
differential range, low supply current, and tight load-reg-
ulation characteristics. The MAX1845 is simple and easy
to compensate.
Single-stage buck conversion allows the MAX1845 to
directly step down high-voltage batteries for the highest
possible efficiency. Alternatively, two-stage conversion
(stepping down the 5V system supply instead of the bat-
tery at a higher switching frequency) allows the minimum
possible physical size.
The MAX1845 is intended for generating chipset, DRAM,
CPU I/O, or other low-voltage supplies down to 1V. For a
single-output version, refer to the MAX1844 data sheet.
The MAX1845 is available in 28-pin QSOP and 36-pin
thin QFN packages.
Features
Ultra-High Efficiency
Accurate Current-Limit Option
Quick-PWM™ with 100ns Load-Step Response
Dual Mode™ Fixed 1.8V/1.5V/Adj or 2.5V/Adj Outputs
Adjustable 1V to 5.5V Output Range
2V to 28V Battery Input Range
200/300/420/540kHz Nominal Switching Frequency
Adjustable Overvoltage Protection
1.7ms Digital Soft-Start
Drives Large Synchronous-Rectifier FETs
2V ±1% Reference Output
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX1845EEI
-40°C to +85°C
28 QSOP
MAX1845ETX
-40°C to +85°C
36 Thin QFN
6mm ✕ 6mm
Applications
Minimal Operating Circuit
Notebook Computers
CPU Core Supplies
Chipset/RAM Supply as Low as 1V
1.8V and 2.5V I/O Supplies
5V INPUT
BATTERY
4.5V TO 28V
V DD
V+
V CC
UVP
OVP
MAX1845EEI
ILIM1
ILIM2
ON1
ON2
BST1
BST2
OUTPUT1
1.8V
DH1
DH2
OUTPUT2
2.5V
LX1
LX2
DL1
TON
OUT1
DL2
CS2
CS1
PGOOD
OUT2
REF
SKIP
FB1
FB2
Pin Configurations appear at end of data sheet.
Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products.
GND
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1% V OUT Accuracy over Line and Load
Power-Good Window Comparator
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Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
ABSOLUTE MAXIMUM RATINGS (Note 1)
V+ to AGND..............................................................-0.3 to +30V
V CC to AGND............................................................-0.3V to +6V
V DD to PGND............................................................-0.3V to +6V
AGND to PGND .....................................................-0.3V to +0.3V
PGOOD, OUT_ to AGND..........................................-0.3V to +6V
OVP, UVP, ILIM_, FB_, REF,
SKIP, TON, ON_ to AGND......................-0.3V to (V CC + 0.3V)
DL_ to PGND ..............................................-0.3V to (V DD + 0.3V)
BST_ to AGND........................................................-0.3V to +36V
CS_ to AGND.............................................................-6V to +30V
DH1 to LX1 ..............................................-0.3V to (V BST1 + 0.3V)
LX_ to BST_ ..............................................................-6V to +0.3V
DH2 to LX2 ..............................................-0.3V to (V BST2 + 0.3V)
REF Short Circuit to GND ...........................................Continuous
Continuous Power Dissipation (T A = +70°C)
28-Pin QSOP (derate 10.8mW/°C above +70°C)........860mW
36-Pin 6mm ✕ 6mm Thin QFN
(derate 26.3mW/°C above +70°C) .............................2105mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1: For the MAX1845EEI, AGND and PGND refer to a single pin designated GND.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V DD = V CC = 5V, SKIP = AGND, V+ = 15V, T A = 0°C to +85°C , typical values are at +25°C, unless otherwise
noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX UNITS
PWM CONTROLLERS
Input Voltage Range
V+
Battery voltage, V+
2
28
V
V CC /V DD V CC , V DD
4.5
5.5
V+ = 2V to 28V, I LOAD
= 0 to 8A, SKIP = V CC ,
+25°C to +85°C
FB1 to AGND
1.782
1.8
1.818
FB1 to V CC
1.485
1.5
1.515
DC Output Voltage OUT1
(Note 2)
FB1 to OUT1
0.99
1
1.01
V OUT1
V
V+ = 2V to 28V, I LOAD
= 0 to 8A, SKIP = V CC ,
0°C to +85°C
FB1 to AGND
1.773
1.8
1.827
FB1 to V CC
1.477
1.5
1.523
FB1 to OUT1
0.985
1
1.015
V+ = 4.5V to 28V,
I LOAD = 0 to 4A,
SKIP = V CC ,
+25°C to +85°C
FB2 to AGND
2.475
2.5
2.525
DC Output Voltage OUT2
(Note 2)
FB2 to OUT2
0.99
1
1.01
V OUT2
V
V+ = 4.5V to 28V,
I LOAD = 0 to 4A,
SKIP = V CC ,
0°C to +85°C
FB2 to AGND
2.463
2.5
2.537
FB2 to OUT2
0.985
1
1.015
Output Voltage Adjust Range
OUT1, OUT2
1
5.5
V
Dual-Mode Threshold, Low
OVP, FB_
0.05
0.1
0.15
V
Dual-Mode Threshold, High
OVP, ILIM_
V CC -
1.5
V CC -
0.4
V
FB1
1.9
2.0
2.1
OUT_ Input Resistance
R OUT1 V OUT1 = 1.5V
75
k Ω
R OUT2 V OUT2 = 2.5V
100
FB_ Input Bias Current
I FB
-0.1
0.1
µA
Soft-Start Ramp Time
Zero to full ILIM
1700
µs
2 _______________________________________________________________________________________
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Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V DD = V CC = 5V, SKIP = AGND, V+ = 15V, T A = 0°C to +85°C , typical values are at +25°C, unless otherwise
noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX UNITS
TON = AGND
120
137
153
On-Time, Side 1 (Note 3)
t ON1
V+ = 24V,
V OUT1 = 2V
TON = REF
153
174
195
ns
TON = float
222
247
272
TON = V CC
316
353
390
TON = AGND
160
182
204
On-Time, Side 2 (Note 3)
t ON2
V+ = 24V,
V OUT2 = 2V
TON = REF
205
234
263
ns
TON = float
301
336
371
TON = V CC
432
483
534
TON = AGND
125
135
145
On-time 2 with
respect to on-
time 1
On-Time Tracking (Note 3)
TON = REF
125
135
145
%
TON = float
125
135
145
TON = V CC
125
135
145
Minimum Off-Time (Note 3)
t OFF
400
500
ns
Quiescent Supply Current (V CC )
I CC
FB_ forced above the regulation point
1100
1500
µA
Quiescent Supply Current (V DD )
I DD
FB_ forced above the regulation point
<1
5
µA
Quiescent Supply Current (V+)
I+
Measured at V+
25
70
µA
Shutdown Supply Current (V CC )
ON1 = ON2 = AGND, OVP = V CC or AGND
<1
5
µA
ON1 = ON2 = AGND, V OVP = 1.8V
1
5
Shutdown Supply Current (V DD )
ON1 = ON2 = AGND
<1
5
µA
Shutdown Supply Current (V+)
ON1 = ON2 = AGND, measured at V+,
V CC = AGND or 5V
<1
5
µA
Reference Voltage
V REF
V CC = 4.5V to 5.5V, no external REF load
1.98
2
2.02
V
Reference Load Regulation
I REF = 0 to 50µA
0.01
V
REF Sink Current
REF in regulation
10
µA
REF Fault Lockout Voltage
Falling edge, hysteresis = 40mV
1.6
V
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
OVP = AGND, with respect to error-
comparator trip threshold
112
114
117
%
1V < V OVP < 1.8V, external feedback,
measured at FB_ with respect to V OVP
-28
0
28
mV
Overvoltage Comparator Offset
(Adjustable-Threshold Mode)
1V < V OVP < 1.8V, internal feedback,
measured at OUT_ with respect to OUT_
regulation point
-3.5
0
+3.5
%
OVP Input Leakage Current
1V < V OVP < 1.8V
-100
<1
100
nA
Overvoltage Fault Propagation
Delay
FB_ forced 2% above trip threshold
1.5
µs
Output Undervoltage Threshold
UVP = V CC , with respect to error-comparator
trip threshold
65
70
75
%
Output Undervoltage Protection
Blanking Time
From ON_ signal going high
10
30
ms
_______________________________________________________________________________________ 3
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Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V DD = V CC = 5V, SKIP = AGND, V+ = 15V, T A = 0°C to +85°C , typical values are at +25°C, unless otherwise
noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX UNITS
Current-Limit Threshold (Fixed)
AGND - V CS _, ILIM_ = V CC
40
50
60
mV
Current-Limit Threshold
(Adjustable)
AGND - V CS _, ILIM_ = 0.5V
40
50
60
mV
AGND - V CS _, ILIM_ = 1V
85
100
115
ILIM_ Adjustment Range
V ILIM _
0.3
2.5
V
Negative Current-Limit Threshold
(Fixed)
V CS _ - AGND, ILIM_ = V CC , T A = +25 o C
-75
-60
-45
mV
Thermal Shutdown Threshold
Hysteresis = 15 o C
160
o
C
V CC Undervoltage Lockout
Threshold
Rising edge, hysteresis = 20mV, PWMs
disabled below this level
4.05
4.4
V
DH Gate-Driver On-Resistance
(Note 4)
BST - LX forced to 5V
MAX1845EEI
1.5
5
Ω
MAX1845ETX
1.5
6
Ω
DL Gate-Driver On-Resistance
(Note 4)
DL, high state
MAX1845EEI
1.5
5
Ω
MAX1845ETX
1.5
6
Ω
DL Gate-Driver On-Resistance
(Note 4)
DL, low state
MAX1845EEI
0.5
1.7
Ω
MAX1845ETX
0.5
2.7
Ω
DH_ Gate Driver Source/Sink
Current
V DH _ = 2.5V, V BST _ = V LX _ = 5V
1
A
DL_ Gate Driver Sink Current
V DL _ = 2.5V
3
A
DL_ Gate Driver Source Current
V DL _ = 2.5V
1
A
ON_, SKIP
2.4
Logic Input High Voltage
V IH
UVP
V CC -
0.4
V
Logic Input Low Voltage
V IL
ON_, SKIP
0.8
V
UVP
0.05
V CC level
V CC -
0.4
TON Input Logic level
Float level
3.15
3.85
V
REF level
1.65
2.35
AGND level
0.5
Logic Input Current
TON (AGND or V CC )
-3
3
µA
Logic Input Current
ON_, SKIP, UVP
-1
1
µA
PGOOD Trip Threshold (Lower)
With respect to error-comparator trip
threshold, falling edge
-12.5
-10
-7.5
%
PGOOD Trip Threshold (Upper)
With respect to error-comparator trip
threshold, rising edge
+7.5
+10
+12.5
%
PGOOD Propagation Delay
Falling edge, FB_ forced 2% below PGOOD
trip threshold
1.5
µs
PGOOD Output Low Voltage
I SINK = 1mA
0.4
V
PGOOD Leakage Current
High state, forced to 5.5V
1
µA
4 _______________________________________________________________________________________
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Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V DD = V CC = 5V, SKIP = AGND, V+ = 15V, T A = -40°C to +85°C , unless otherwise noted.) (Note 5)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
PWM CONTROLLERS
Input Voltage Range
V+
Battery voltage, V+
2
28
V
V CC /V DD V CC , V DD
4.5
5.5
FB1 to AGND
1.773
1.827
V+ = 2V to 28V, SKIP = V CC ,
I LOAD = 0 to 10A
DC Output Voltage, OUT1 (Note 2)
V OUT1
FB1 to V CC
1.477
1.523
V
FB1 to OUT1
0.985
1.015
DC Output Voltage, OUT2 (Note 2)
V OUT2
V+ = 2V to 28V, SKIP = V CC ,
I LOAD = 0 to 10A
FB2 to AGND
2.463
2.537
V
FB2 to OUT2
0.985
1.015
Output Voltage Adjust Range
OUT1, OUT2
1
5.5
V
Dual-Mode Threshold (Low)
OVP, FB_
0.05
0.15
V
Dual-Mode Threshold (High)
OVP, ILIM_
V CC -
1.5
V CC -
0.4
V
FB_
1.9
2.1
OUT_ Input Resistance
R OUT1 V OUT1 = 1.5V
75
k Ω
R OUT2 V OUT2 = 2.5V
100
FB_ Input Bias Current
I FB
-0.1
0.1
µA
TON = AGND
120
153
On-Time, Side 1 (Note 3)
t ON1
V+ = 24V, V OUT1 = 2V
TON = REF
153
195
ns
TON = float
217
272
TON = V CC
308
390
TON = AGND
160
204
On-Time, Side 2 (Note 3)
t ON2
V+ = 24V, V OUT2 = 2V
TON = REF
205
263
ns
TON = float
295
371
TON = V CC
422
534
TON = AGND
125
145
On-Time Tracking (Note 3)
On-time 2, with
respect to on-time 1
TON = REF
125
145
%
TON = float
125
145
TON = V CC
125
145
Minimum Off-Time (Note 3)
t OFF
500
ns
Quiescent Supply Current (V CC )
I CC
FB forced above the regulation point
1500
µA
Quiescent Supply Current (V DD )
I DD
FB forced above the regulation point
5
µA
Quiescent Supply Current (V+)
I+
Measured at V+
70
µA
Reference Voltage
V REF
V CC = 4.5V to 5.5V, no external REF load
1.98
2.02
V
Reference Load Regulation
I REF = 0 to 50uA
0.01
V
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
OVP = GND, with respect to FB_ regulation
point, no load
112
117
%
Output Undervoltage Threshold
UVP = V CC , with respect to FB_ regulation
point, no load
65
75
%
Current-Limit Threshold (Fixed)
AGND - V CS _, ILIM_ = V CC
35
65
mV
_______________________________________________________________________________________ 5
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