MAX8654ETX+ Maxim Integrated Products, MAX8654ETX+ Datasheet - Page 12

• Manufacturer Part Number: MAX8654ETX+
• Description: IC REG STP DWN 12V 8A 36TQFN
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX8654ETX+

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 11.9 V
• Current - Output: 8A
• Frequency - Switching: 250kHz ~ 1.2MHz
• Voltage - Input: 4.5 ~ 14 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-TQFN Exposed Pad
• Power - Output: 2.86W
• Output Voltage: 0.6 V to 0.85 V
• Output Current: 8 A
• Input Voltage: 4.5 V to 14 V
• Switching Frequency: 1 MHz
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

12V, 8A 1.2MHz
Step-Down Regulator
The UVLO circuitry inhibits switching when V
is below 4.20V (typ) or V
voltages are above the thresholds, UVLO clears and
the soft-start function activates; 100mV of hysteresis is
built in for glitch immunity.
The gate-drive voltage for the high-side, n-channel
switch is generated by a flying capacitor boost circuit.
The capacitor between BST and LX is charged from the
VDL supply while the low-side MOSFET is on. When the
low-side MOSFET is switched off, the stored voltage of
the capacitor is stacked above LX to provide the neces-
sary turn-on voltage for the high-side internal MOSFET.
The switching frequency in fixed-frequency PWM oper-
ation is resistor programmable from 250kHz to 1.2MHz.
Set the switching frequency of the IC with a resistor
(R
where f
The MAX8654 features a SYNC function that allows the
switching frequency to be synchronized to any external
clock frequency that is higher than the internal clock
frequency. Drive SYNC with a square wave at the
desired synchronization frequency. A rising edge on
SYNC triggers the internal SYNC circuitry. Connect
SYNC to GND to disable the function and operate with
the internal oscillator.
The SYNCOUT output generates a clock signal that is
180° out-of-phase with its internal oscillator, or the sig-
nal applied to SYNC. This allows for another MAX8654
to be synchronized 180° out-of-phase to reduce the
input ripple current.
PWRGD is an open-drain output that goes high imped-
ance once the soft-start ramp has concluded, provided
V
V
V
cycles. PWRGD is low during shutdown, when pulled up
to V
12
REFIN
REFIN
REFIN
FREQ
VL
______________________________________________________________________________________
High-Side MOSFET Driver Supply (BST)
.
. PWRGD pulls low when V
) from FREQ to GND. R
S
is above 0.54V and V
and V
is the desired switching frequency in MHz.
SYNC Function (SYNC, SYNCOUT)
R
FREQ
REFIN
Undervoltage Lockout (UVLO)
Power-Good Output (PWRGD)
=
is less than 0.54V for 48 clock
52 63
Frequency Select (FREQ)
.
VL
×
⎛
⎜
⎝
is below 3V. Once these
FB
FREQ
f
1
S
is greater than 90% of
−
FB
0 05
is calculated as:
.
is less than 90% of
⎞
⎟ Ω
⎠
k
IN
or V
VDL
Drive EN to GND to shut down the IC and reduce qui-
escent current to 10μA (typ). During shutdown, the out-
puts of the MAX8654 are high impedance. Drive EN
high to enable the MAX8654.
Thermal-overload protection limits total power dissipa-
tion in the device. When the junction temperature
exceeds T
device into shutdown, allowing the die to cool. The ther-
mal sensor turns the device on again after the junction
temperature cools by 20°C, causing a pulsed output
during continuous overload conditions. The soft-start
sequence begins after a thermal-shutdown condition.
To decrease the noise effects due to the high switching
frequency and maximize the output accuracy of the
MAX8654, decouple VDL with a minimum of 2.2μF
ceramic capacitor from VDL to PGND. Also, decouple
VL with a 1μF ceramic capacitor from VL to GND. Place
these capacitors as close to the respective pins as pos-
sible.
Choose an inductor with the following equation:
where LIR is the ratio of the inductor ripple current to
average continuous current at the minimum duty cycle.
Choose LIR between 20% to 40% for best performance
and stability.
Use a low-loss inductor with the lowest possible DC
resistance that fits in the allotted dimensions. Powered
iron-ferrite core types are often the best choice for per-
formance. With any core material, the core must be
large enough not to saturate at the peak inductor cur-
rent (I
PEAK
). Calculate I
J
L
=
I
= +165°C, a thermal sensor forces the
PEAK
f x V x LIR x I
Applications Information
S
V
OUT
= +
IN
(
1
PEAK
x V
LIR
(
VL and VDL Decoupling
2
IN
)
as follows:
−
x I
OUT MAX
Thermal Protection
V
OUT MAX
Inductor Selection
OUT
(
Shutdown Mode
(
)
)
)