MAX5951ETJ+ Maxim Integrated Products, MAX5951ETJ+ Datasheet - Page 14

• Manufacturer Part Number: MAX5951ETJ+
• Description: IC BUCK PWM CTRLR 12V/5V 32-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX5951ETJ+

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 5.5 V
• Current - Output: 10A
• Frequency - Switching: 100kHz ~ 1MHz
• Voltage - Input: 8 ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Power - Output: 2.76W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The output of the internal error amplifier (COMP) is
available for frequency compensation (see the
Compensation Design Guidelines section). The invert-
ing input is FB; the output is COMP. The error amplifier
has an 80dB open-loop gain and a 2.5MHz GBW prod-
uct. See the Typical Operating Characteristics for the
Open-Loop Gain and Phase vs. Frequency graph.
An internal ramp is compared against the output of the
error amplifier to generate the PWM signal. The ampli-
tude of the ramp, V
The current-limit circuit employs a lossless valley cur-
rent-limiting algorithm that uses the MOSFET’s on-resis-
tance as the current-sensing element. Once the
high-side MOSFET turns off, the voltage across the low-
side MOSFET is monitored. If the voltage across the
low-side MOSFET (R
exceed the current-limit threshold, the high-side MOS-
FET turns on normally at the start of the next cycle. If
the voltage across the low-side MOSFET exceeds the
current-limit threshold just before the beginning of a
new PWM cycle, the controller skips that cycle. During
severe overload or short-circuit conditions, the switch-
ing frequency of the device appears to decrease
because the on-time of the low-side MOSFET extends
beyond a clock cycle.
If the current-limit threshold is exceeded for eight cumu-
lative clock cycles (N
DH and DL are pulled low) for 512 clock cycles (hiccup
timeout) and restarts with a soft-start sequence. If three
consecutive cycles pass without a current-limit event, the
12V/5V Input Buck PWM Controller
Figure 2. Hiccup Block Diagram
14
CURRENT LIMIT
______________________________________________________________________________________
Output Short-Circuit Protection
RAMP,
IN
CLR
IN
CLR
CL
COUNT OF 8
COUNT OF 3
DS(ON)
), the device shuts down (both
N
N
is 1.8V.
CLR
CL
x I
PWM Comparator
INDUCTOR
Error Amplifier
(Hiccup Mode)
INITIATE HICCUP
) does not
TIMEOUT
N
HT
count of N
protects against continuous output short circuit.
The MAX5951 features an integrated thermal-overload
protection with temperature hysteresis. Thermal-over-
load protection limits the total power dissipation in the
device and protects it in the event of an extended ther-
mal fault condition. When the die temperature exceeds
+135°C, an internal thermal sensor shuts down the
device, turning off the power MOSFETs and allowing
the die to cool. After the die temperature falls by
+15°C, the part restarts with a soft-start sequence.
Connect an external resistive divider from IN to PUVLO
to AGND to override the internal PWM UVLO divider.
The rising threshold at PUVLO is set to 1.220V with
120mV hysteresis. First select the PUVLO to AGND
resistor (R2), then calculate the resistor from IN to
PUVLO (R1) using the following equation:
where V
needs to turn on, V
to be less than 20kΩ. See Figure 3.
Leave PUVLO unconnected for the default PWM UVLO
threshold. In this case, an internal voltage-divider moni-
tors the supply voltage at IN and allows startup when
IN rises above 7V (typ).
Figure 3. External PWM UVLO Divider
IN
CL
is the input voltage at which the converter
Setting the Undervoltage Lockout
is cleared (see Figure 2). Hiccup mode
R
Thermal-Overload Protection
1
PWM Controller Design
PUVLO
PUVLO
=
R
2
×
⎡
⎢
⎣
= 1.220V, and R2 is chosen
V
PUVLO
IN
V
IN
R2
R1
−
1
Procedures
⎤
⎥
⎦