19-1993; Rev 3; 9/02
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
MAX1844
General Description
The MAX1844 pulse-width modulation (PWM) controller
provides high efficiency, excellent transient response,
and high DC output accuracy needed for stepping
down high-voltage batteries to generate low-voltage
CPU core or chipset/RAM supplies in notebook com-
puters.
Maxim’s proprietary Quick-PWM™ quick-response,
constant-on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides
100ns “instant-on” response to load transients while
maintaining a relatively constant switching frequency.
Efficiency is enhanced by an ability to drive very large
synchronous-rectifier MOSFETs. Accurate current sens-
ing to ensure reliable overload protection is available
using an external current-sense resistor in series with
the synchronous rectifier. Alternatively, the synchronous
rectifier itself can be used for less accurate current
sensing at the lowest possible power dissipation.
Single-stage buck conversion allows the MAX1844 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
battery) at a higher switching frequency allows the mini-
mum possible physical size.
The MAX1844 is intended for CPU core, chipset,
DRAM, or other low-voltage supplies as low as 1V. It is
available in 20-pin QSOP, and QFN packages and
includes both adjustable overvoltage and undervoltage
protection.
For a dual step-down PWM controller with accurate cur-
rent limit, refer to the MAX1845. The MAX1714/ MAX1715
single/dual PWM controllers are similar to the MAX1844/
MAX1845 but do not use current-sense resistors.
o
Ultra-High Efficiency
o
Accurate Current-Limit Option
o
Quick-PWM with 100ns Load-Step Response
o
1% V
OUT
Accuracy Over Line and Load
o
1.8V/2.5V Fixed or 1V to 5.5V Adjustable Output
Range
o
2V to 28V Battery Input Range
o
200/300/450/600kHz Switching Frequency
o
Adjustable Overvoltage Protection
o
Adjustable Undervoltage Protection
o
1.7ms Digital Soft-Start
o
Drives Large Synchronous-Rectifier FETs
o
2V ±1% Reference Output
o
Power-Good Window Comparator
KIT
ATION
EVALU
BLE
AVAILA
Features
Ordering Information
PART
MAX1844EEP
MAX1844EGP*
MAX1844ETP
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
20 QSOP
20 QFN
20 Thin QFN
Minimal Operating Circuit
BATTERY
4.5V TO 28V
5V INPUT
V
CC
SHDN
UVP
ILIM
BST
DH
MAX1844
LX
REF
DL
PGOOD
LATCH
CS
OUT
SKIP
GND
OUTPUT
2.5V
V
DD
V+
Applications
Notebook Computers
CPU Core Supplies
Chipset/RAM Supplies as Low as 1V
1.8V and 2.5V Supplies
*Contact
factory for availability.
Quick-PWM is a trademark of Maxim Integrated Products.
Pin Configuration appears at end of data sheet.
OVP
FB
________________________________________________________________
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.
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
MAX1844
ABSOLUTE MAXIMUM RATINGS
V+ to GND ..............................................................-0.3V to +28V
V
CC
, V
DD
to GND .....................................................-0.3V to +6V
OUT, PGOOD,
SHDN
to GND ..................................-0.3V to +6V
FB, ILIM,
LATCH,
OVP, REF,
SKIP,
TON, UVP to GND ..................................-0.3V to (V
CC
+ 0.3V)
BST to GND ............................................................-0.3V to +34V
CS to GND.................................................................-6V to +30V
DL to GND ..................................................-0.3V to (V
DD
+ 0.3V)
DH to LX .....................................................-0.3V to (BST + 0.3V)
LX to BST..................................................................-6V to +0.3V
REF Short Circuit to GND ...........................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
20-Pin QSOP (derate 9.1mW/°C above +70°C)...........727mW
20-Pin 5mm
✕
5mm QFN (derate 20.0mW/°C
above +70°C).................................................................1.60W
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
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+ = 15V, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.)
PARAMETER
Input Voltage Range
Error Comparator Threshold
(DC Output Voltage Accuracy)
(Note 1)
Load Regulation Error
Line Regulation Error
FB Input Bias Current
Output Adjustment Range
OUT Input Resistance
Soft-Start Ramp Time
FB = GND
FB = V
CC
or adjustable feedback mode
Rising edge of
SHDN
to full current limit
TON = GND (600kHz)
On-Time
V+ = 24V,
V
OUT
= 2V
(Note 2)
(Note 2)
FB forced above the regulation point
FB forced above the regulation point
SHDN
= GND
SHDN
= GND
SHDN
= GND, V+ = 28V, V
CC
= V
DD
= 0 or 5V
V
CC
= 4.5V to 5.5V, no external REF load
I
REF
= 0 to 50µA
1.98
TON = REF (450kHz)
TON = unconnected (300kHz)
TON = V
CC
(200kHz)
Minimum Off-Time
Quiescent Supply Current (V
CC
)
Quiescent Supply Current (V
DD
)
Quiescent Supply Current (V+)
Shutdown Supply Current (V
CC
)
Shutdown Supply Current (V
DD
)
Shutdown Supply Current (V+)
Reference Voltage
Reference Load Regulation
140
175
260
380
Battery voltage, V+
V
CC
, V
DD
FB = OUT
V+ = 4.5V to 28V,
SKIP
= V
CC
I
LOAD
= 0 to 3A,
SKIP
= V
CC
V
CC
= 4.5V to 5.5V, V+ = 4.5V to 28V
-0.1
1
90
70
190
145
1.7
160
200
290
425
400
550
<1
25
<1
<1
<1
2.00
180
225
320
470
500
800
5
40
5
5
5
2.02
0.01
ns
µA
µA
µA
µA
µA
µA
V
V
ns
FB = GND
FB = V
CC
CONDITIONS
MIN
2
4.5
0.99
2.475
1.782
2.5
1.8
9
5
+0.1
5.5
350
270
TYP
MAX
28
5.5
1.01
2.525
1.818
mV
mV
µA
V
kΩ
ms
V
UNITS
V
2
_______________________________________________________________________________________
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.)
PARAMETER
REF Sink Current
REF Fault Lockout Voltage
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
REF in regulation
Falling edge, hysteresis = 40mV
With respect to error comparator threshold, no load
OVP = GND, rising edge, hysteresis = 1%
External feedback, measured at FB with respect to
V
OVP
, 1V < V
OVP
< 1.8V, rising edge, hysteresis =1%
Overvoltage Comparator Offset
(Adjustable-Threshold Mode)
Internal feedback, measured at OUT with respect to the
nominal OUT regulation voltage, 1V < V
OVP
< 1.8V,
rising edge, hysteresis = 1%
1V < V
OVP
< 1.8V
FB forced 2% above trip threshold
12
-30
CONDITIONS
MIN
10
1.6
14.5
17
+30
TYP
MAX
UNITS
µA
V
%
mV
MAX1844
-3.5
-100
0
1.5
+3.5
+100
%
nA
µs
OVP Input Leakage Current
Overvoltage Fault
Propagation Delay
Output Undervoltage Protection
Trip Threshold (Fixed-Threshold
Mode)
Output Undervoltage Protection
Trip Threshold (Adjustable-
Threshold Mode)
UVP Input Leakage Current
Output Undervoltage Protection
Blanking Time
PGOOD Trip Threshold (Lower)
PGOOD Trip Threshold (Upper)
PGOOD Propagation Delay
PGOOD Output Low Voltage
PGOOD Leakage Current
ILIM Adjustment Range
Current-Limit Threshold (Fixed)
Current-Limit Threshold
(Adjustable)
Current-Limit Threshold
(Negative Direction)
Current-Limit Threshold
(Zero Crossing)
Thermal Shutdown Threshold
V
CC
Undervoltage
Lockout Threshold
With respect to error comparator threshold, UVP = V
CC
External feedback, measured at FB with respect to
V
UVP
, 0.4V < V
UVP
< 1V
Internal feedback, measured at OUT with respect to the
nominal OUT regulation voltage, 0.4V < V
UVP
< 1V
0.4V < V
UVP
< 1V
From rising edge of
SHDN
With respect to error comparator threshold, no load
With respect to error comparator threshold, no load
FB forced 2% beyond PGOOD trip threshold, falling
I
SINK
= 1mA
High state, forced to 5.5V
65
70
75
%
-40
-5
-100
10
-12.5
8
-10
10
10
<1
+40
+5
+100
30
-8
12.5
0.4
1
mV
%
nA
ms
%
%
µs
V
µA
V
mV
mV
mV
mV
°C
0.25
GND - V
CS
, ILIM = V
CC
GND - V
CS
V
ILIM
= 0.5V
V
ILIM
= 2V
90
40
170
-140
100
50
200
-117
3
150
4.1
3
110
60
230
-95
GND - V
CS
,
SKIP
= V
CC
, ILIM = V
CC
,T
A
= +25°C
GND - V
CS,
SKIP
= GND
Hysteresis = 10°C
Rising edge, hysteresis = 20mV,
PWM disabled below this level
4.4
V
_______________________________________________________________________________________
3
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
MAX1844
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.)
PARAMETER
DH Gate-Driver On-Resistance
(Note 4)
DL Gate-Driver On-Resistance
(Note 4)
DL Gate-Driver On-Resistance
(Note 4)
DH Gate-Driver Source/Sink
Current
DL Gate-Driver Source Current
DL Gate-Driver Sink Current
Dead Time
Logic Input High Voltage
Logic Input Low Voltage
Logic Input Current
Dual Mode Threshold, Low
Dual Mode Threshold, High
TON V
CC
Level
TON Float Voltage
TON Reference Level
TON GND Level
TON Input Current
ILIM Input Leakage Current
Forced to GND or V
CC
-3
-100
0
CONDITIONS
BST - LX forced to 5V
DL, high state
DL, low state
MAX1844EEP
MAX1844EGP, MAX1844ETP
MAX1844EEP
MAX1844EGP, MAX1844ETP
MAX1844EEP
MAX1844EGP, MAX1844ETP
MIN
TYP
1.5
1.5
1.5
1.5
0.5
0.5
1
1
3
35
26
2.4
0.8
-1
0.15
V
CC
- 1.5
1.9
V
CC
- 0.4
3.15
1.65
3.85
2.35
0.5
+3
+100
2.0
0.20
+1
0.25
V
CC
- 0.4
2.1
MAX
5
6
5
6
1.7
2.7
UNITS
Ω
Ω
Ω
A
A
A
ns
V
V
µA
V
V
V
V
V
V
µA
nA
DH forced to 2.5V, BST-LX forced to 5V
DL forced to 2.5V
DL forced to 5V
DL rising
DH rising
LATCH, SHDN, SKIP
LATCH, SHDN, SKIP
LATCH, SHDN, SKIP
OVP, UVP, FB
OVP, UVP
FB
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 3)
PARAMETER
Input Voltage Range
Error Comparator Threshold
(DC Output Voltage Accuracy)
(Note 1)
Battery voltage, V+
V
CC
, V
DD
V+ = 4.5V to 28V,
SKIP
= V
CC
FB = OUT
FB = GND
FB = V
CC
TON = GND
On-Time
V+ = 24V,
V
OUT
= 2V
(Note 2)
TON = REF(450kHz)
TON = Unconnected
TON = V
CC
(200kHz)
(300kHz)
(600kHz)
CONDITIONS
MIN
2
4.5
0.985
2.462
1.773
140
175
260
380
TYP
MAX
28
5.5
1.015
2.538
1.827
180
225
320
470
ns
V
UNITS
V
4
_______________________________________________________________________________________
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 3)
PARAMETER
Minimum Off-Time
Quiescent Supply Current (V
CC
)
Quiescent Supply Current (V
DD
)
Quiescent Supply Current (V+)
Shutdown Supply Current (V
CC
)
Shutdown Supply Current (V
DD
)
Shutdown Supply Current (V+)
Reference Voltage
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
(Note 2)
FB forced above the regulation point
FB forced above the regulation point
Measured at V+
SHDN
= GND
SHDN
= GND
SHDN
= GND, V+ = 28V, V
CC
= V
DD
= 0 or 5V
V
CC
= 4.5V to 5.5V, no external REF load
With respect to error comparator threshold, no load
OVP = GND, rising edge, hysteresis = 1%
External feedback, measured at FB with respect to
V
OVP
, 1V < V
OVP
1.8V, rising edge, hysteresis = 1%
Internal feedback, measured at OUT with respect to the
nominal OUT regulation voltage, 1V < V
OVP
< 1.8V
With respect to error comparator threshold, no load
OUT falling edge, hysteresis = 1%
With respect to error comparator threshold, no load
OUT rising edge, hysteresis = 1%
I
SINK
= 1mA
High state, forced to 5.5V
GND - V
CS
, ILIM = V
CC
GND - V
CS
, V
ILIM
= 0.5V
GND - V
CS
, V
ILIM
= 2V
Rising edge, hysteresis = 20mV,
PWM disabled below this level
LATCH, SHDN, SKIP
LATCH, SHDN, SKIP
LATCH, SHDN, SKIP
-1
85
35
160
4.1
2.4
0.8
1
1.98
12
-30
-3.5
-12.5
7.5
CONDITIONS
MIN
TYP
MAX
500
800
5
40
5
5
5
2.02
17
+30
+3.5
-7.5
12.5
0.4
1
115
65
240
4.4
UNITS
ns
µA
µA
µA
µA
µA
µA
V
%
mV
%
%
%
V
µA
mV
mV
V
V
V
µA
MAX1844
Overvoltage Comparator Offset
(Adjustable-Threshold Mode)
PGOOD Trip Threshold (Lower)
PGOOD Trip Threshold (Upper)
PGOOD Output Low Voltage
PGOOD Leakage Current
Current-Limit Threshold (Fixed)
Current-Limit Threshold
(Adjustable)
V
CC
Undervoltage
Lockout Threshold
Logic Input High Voltage
Logic Input Low Voltage
Logic Input Current
Note 1:
When the inductor is in continuous conduction, the output voltage will have a DC regulation level higher than the error com-
parator threshold by 50% of the ripple. In discontinuous conduction (SKIP = GND, light load), the output voltage will have a
DC regulation level higher than the trip level by approximately 1.5% due to slope compensation.
Note 2:
On-time and off-time specifications are measured from 50% point to 50% point at the DH pin with LX = GND, V
BST
= 5V,
and a 250pF capacitor connected from DH to LX. Actual in-circuit times may differ due to MOSFET switching speeds.
Note 3:
Specifications to -40°C are guaranteed by design, not production tested.
Note 4:
Production testing limitations due to package handling require relaxed maximum on-resistance specifications for the QFN
package. The MAX1844EEP, MAX1844EGP, and MAX1844ETP contain the same die and the QFN package imposes no
additional resistance in-circuit.
_______________________________________________________________________________________
5
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