MAX1844ETP+ Maxim Integrated Products, MAX1844ETP+ Datasheet - Page 21

• Manufacturer Part Number: MAX1844ETP+
• Description: IC CNTRLR STP DWN HS 20-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1844ETP+

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.8V, 2.5V, Adj
• Current - Output: 4A
• Frequency - Switching: 200kHz, 300kHz, 450kHz, 600kHz
• Voltage - Input: 2 ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-TQFN Exposed Pad
• Power - Output: 727mW
• Output Voltage: 1 V to 5.5 V, 1.8 V, 2.5 V
• Output Current: 4000 mA
• Mounting Style: SMD/SMT
• Switching Frequency: 600 KHz
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Synchronous Pin: No
• Topology: Buck
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Therefore, V
very large output capacitance, and a practical input volt-
age with reasonable output capacitance would be 3.48V.
Careful PC board layout is critical to achieving low
switching losses and clean, stable operation. The switch-
ing power stage requires particular attention (Figure 9). If
possible, mount all of the power components on the top
side of the board, with their ground terminals flush
against one another. Follow these guidelines for good
PC board layout:
• Keep the high-current paths short, especially at the
• Keep the power traces and load connections short.
• Minimize current sensing errors by connecting CS
• When trade-offs in trace lengths must be made, it is
• Route high-speed switching nodes (BST, LX, DH, and
1) Place the power components first, with ground termi-
2) Mount the controller IC adjacent to MOSFET Q2,
3) Group the gate-drive components (BST diode and
Accurate Current Limit for Notebook Computers
ground terminals. This practice is essential for stable,
jitter-free operation.
This practice is essential for high efficiency. Using
thick copper PC boards (2oz vs. 1oz) can enhance
full-load efficiency by 1% or more. Correctly routing
PC board traces is a difficult task that must be
approached in terms of fractions of centimeters,
where a single milliohm of excess trace resistance
causes a measurable efficiency penalty.
directly to the R
preferable to allow the inductor charging path to be
made longer than the discharge path. For example,
it is better to allow some extra distance between the
input capacitors and the high-side MOSFET than to
allow distance between the inductor and the low-
side MOSFET or between the inductor and the out-
put filter capacitor.
DL) away from sensitive analog areas (REF, FB, CS).
nals adjacent (Q2 source, C
possible, make all these connections on the top layer
with wide, copper-filled areas.
preferably on the back side opposite Q2 in order to
keep LX, GND, and the DL gate-drive lines short and
wide. The DL gate trace must be short and wide,
measuring 10 to 20 squares (50 to 100 mils wide if the
MOSFET is 1 inch from the controller IC GND pin.
capacitor, V
controller IC.
IN
DD
must be greater than 3.13V, even with
SENSE
______________________________________________________________________________________
bypass capacitor) together near the
PC Board Layout Guidelines
High-Speed Step-Down Controller with
terminal.
IN-
Layout Procedure
, C
OUT-
, D1 anode). If
TRANSISTOR COUNT: 2963
PROCESS: BiCMOS
4) Make the DC-DC controller ground connections as
5) Connect the output power planes directly to the out-
shown in Figure
having two separate ground planes: power ground,
where all the high-power components go; and an ana-
log ground plane for sensitive analog components.
The analog ground plane and power ground plane
must meet only at a single point directly at the IC.
put filter capacitor positive and negative terminals
with multiple vias. Place the entire DC-DC converter
circuit as close to the load as is practical.
TOP VIEW
OVP
OUT
ILIM
REF
FB
PGOOD
LATCH
SHDN
OVP
OUT
ILIM
UVP
REF
CS
FB
1
2
3
4
5
10
1
2
3
4
5
6
7
8
9
6
20
9.
20 THIN QFN
MAX1844ETP
MAX1844EEP
MAX1844EGP
This diagram can be viewed as
19
7
20 QSOP
18
8
Pin Configuration
Chip Information
17
9
10
16
20
19
18
17
16
15
14
13
12
11
DH
LX
BST
SKIP
V+
TON
V
V
DL
GND
12
15
14
13
11
CC
DD
BST
SKIP
V+
TON
V
CC
21