MAX15034 Datasheet, PDF(13/25 Page) Maxim Integrated Products – Configurable, Single-/Dual-Output, Synchronous Buck Controller for High-Current Applications

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MAX15034 Datasheet, PDF (13/25 Pages) Maxim Integrated Products – Configurable, Single-/Dual-Output, Synchronous Buck Controller for High-Current Applications

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Configurable, Single-/Dual-Output, Synchronous

Buck Controller for High-Current Applications

Hiccup Fault Protection

The MAX15034 includes overload fault protection circuitry

that prevents damage to the power MOSFETs. The fault

protection consists of two digital fault integration blocks

that enable hiccuping under overcurrent conditions. This

circuit works as follows: for every clock cycle the current-

limit threshold is exceeded, the fault integration counter

increments by one count. Thus, if the current-limit condi-

tion persists, the counter reaches its shutdown threshold

in 32,768 counts and shuts down the external MOSFETs.

When the MAX15034 shuts down due to a fault, the

counter begins to count down (since the current-limit con-

dition has ended), once every 16 clock cycles. Thus, the

device counts down for 524,288 clock cycles. At this

point, switching resumes. This produces an effective duty

cycle of 6.25% power-up and 93.75% power-down under

fault conditions. With a switching frequency set to

250kHz, power-up and power-down times are approxi-

mately 131ms and 2.09s, respectively.

Control Loop

The MAX15034 uses an average current-mode control

topology to regulate the output voltage. The control

loop consists of an inner current loop and an outer volt-

age loop. The inner current loop controls the output

current, while the outer voltage loop controls the output

voltage. The inner current loop absorbs the inductor

pole, reducing the order of the outer voltage loop to

that of a single-pole system. Figure 2 is the block dia-

gram of OUT1âs control loop.

The current loop consists of a current-sense resistor,

RSENSE, a current-sense amplifier (CA1), a current-

error amplifier (CEA1), an oscillator providing the carri-

er ramp, and a PWM comparator (CPWM1). The

precision current-sense amplifier (CA1) amplifies the

sense voltage across RSENSE by a factor of 36. The

inverting input to CEA1 senses the output of CA1. The

output of CEA1 is the difference between the voltage-

error amplifier output (EAOUT1) and the gained-up volt-

age from CA1. The RC compensation network

connected to CLP1 provides external frequency com-

pensation for the respective CEA1 (see the

Compensation section). The start of every clock cycle

enables the high-side driver and initiates a PWM on-

cycle. Comparator CPWM1 compares the output volt-

age from CEA1 against a 0 to 2V ramp from the

oscillator. The PWM on-cycle terminates when the ramp

voltage exceeds the error voltage from the current-error

amplifier (CEA1).

CSN1

CSP1

CA 1

CLP1

RCF CCF

CCFF

VEA1

CEA1

2VP-P

CPWM1

DRIVE

VREF = 0.61V

VIN

RSENSE

COUT

VOUT1

LOAD

Figure 2. Current and Voltage Loops

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