MAX1714BEEE Maxim Integrated Products, MAX1714BEEE Datasheet - Page 16

• Manufacturer Part Number: MAX1714BEEE
• Description: Current Mode PWM Controllers
• Manufacturer: Maxim Integrated Products

Specifications of MAX1714BEEE

• Number Of Outputs: 1
• Output Voltage: 1 V to 5.5 V
• Output Current: 3000 mA
• Mounting Style: SMD/SMT
• Package / Case: QSOP-16
• 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

High-Speed Step-Down Controller
for Notebook Computers
The switching frequency and inductor operating point
determine the inductor value as follows:
Example: I
f = 300kHz, 33% ripple current or LIR = 0.33.
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice, although powdered iron
is inexpensive and can work well at 200kHz. The core
must be large enough not to saturate at the peak induc-
tor current (I
Most inductor manufacturers provide inductors in stan-
dard values, such as 1.0µH, 1.5µH, 2.2µH, 3.3µH, etc.
Also look for nonstandard values, which can provide a
better compromise in LIR across the input voltage range.
For example, Sumida offers 3.1µH and 4.4µH in their
CDRH125 series. If using a swinging inductor (where the
no-load inductance decreases linearly with increasing
current), evaluate the LIR with properly scaled induc-
tance values.
The inductor ripple current also impacts transient-
response performance, especially at low V
ferentials. Low inductor values allow the inductor
current to slew faster, replenishing charge removed
from the output filter capacitors by a sudden load step.
Table 4. Frequency Selection Guidelines
16
FREQUENCY
TON = AGND
TON = Float
TON = V
TON = REF
(kHz)
200
300
450
600
______________________________________________________________________________________
I
L =
PEAK
CC
L
LOAD(MAX)
=
PEAK
= I
V
IN
4-cell Li+ notebook
4-cell Li+ notebook
3-cell Li+ notebook
+5V input
7V 300kHz 0.33 8A
LOAD(MAX)
APPLICATION
⋅ ⋅
⋅
V
1.5V (7V - 1.5V)
).
OUT
TYPICAL
f
LIR
(V
= 8A, V
IN
⋅
+ [(LIR / 2) · I
⋅
- V
I
LOAD(MAX)
Transient Response
OUT
⋅
IN =
Inductor Selection
Use for absolute best
efficiency.
Considered mainstream
by current standards.
Useful in 3-cell systems
for lighter loads than the
CPU core or where size is
key.
Good operating point for
compound buck designs
or desktop circuits.
)
=
7V, V
COMMENTS
LOAD(MAX)
1.49 H
IN
OUT
µ
- V
= 1.5V,
OUT
]
dif-
The amount of output sag is also a function of the maxi-
mum duty factor, which can be calculated from the on-
time and minimum off-time:
where
and minimum off-time = 400ns typ (see Table 5 for K val-
ues).
The amount of overshoot during a full-load to no-load
transient due to stored inductor energy can be calculated
as:
where I
The minimum current-limit threshold must be high
enough to support the maximum load current. The valley
of the inductor current occurs at I
of the ripple current (Figure 4); therefore:
where I
old voltage divided by the R
MAX1714, the minimum current-limit threshold using the
100mV default setting is 90mV. Use the worst-case maxi-
mum value for R
and add some margin for the rise in R
perature. A good general rule is to allow 0.5% additional
resistance for each °C of temperature rise.
Examining the 8A circuit example with a maximum
R
ing:
This 7.5A is greater than the valley current of 6.7A, so the
circuit can easily deliver the full rated 8A using the default
100mV nominal ILIM threshold.
For an adjustable threshold, connect a two-resistor
divider from REF to AGND, with ILIM connected at the
center tap. The external adjustment range of 0.5V to 2.0V
corresponds to a current-limit threshold of 50mV to
200mV. When adjusting the current limit, use 1% toler-
ance resistors to prevent a significant increase of errors in
DS(ON)
DUTY
I
LIMIT(LOW)
V
PEAK
LIMIT(LOW)
SAG
=
= 12mΩ at high temperature reveals the follow-
K (V
I
LIMIT(LOW)
=
is the peak inductor current.
OUT
2 C
DS(ON)
⋅ ⋅
> I
V
SOAR
F
equals minimum current-limit thresh-
LOAD(MAX)
K (V
+ 0.075V) V
( I
DUTY (V
∆
= 90mV / 12mΩ = 7.5A
from the MOSFET Q2 data sheet,
OUT
LOAD(MAX)
≈
Setting the Current Limit
2C
L I
+ 0.075V) V
OUT OUT
⋅
IN(MIN)
- (LIR / 2) I
PEAK
OUT
DS(ON)
V
LOAD(MAX)
)
2
2
+ min off - time
⋅
- V
L
DS(ON)
of Q2. For the
IN
LOAD(MAX)
OUT
)
minus half
with tem-