MCP16502 datasheet(74/86 Pages) MICROCHIP

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MCP16502

DS20006275D-page 74

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Failing to do so would set the HPM pin low again shortly

after it has been set high, thereby generating a cyclic

behavior where the relevant channel turns on and off

indefinitely.

If the LPM pin goes high (with PWRHLD = High) while

HPM is low, the MCP16502 will move to a Low-Power

state. If HPM goes high after that, the MCP16502 will

ignore it and it will stay in the Low-Power state (as long

as LPM = High).

On the other hand, if HPM goes high first (thus

PWRHLD = HPM = 1, LPM = 0), the device remains in

the HPM state even if LPM is asserted high. To go to

the Low-Power state, HPM must be deasserted first.

5.4

Buck1 Hysteretic Control Mode

(HCM)/B1HCEN Bit

If Buck1 is set in Auto-PFM mode while the input

voltage (e.g., a discharging battery) is decreasing and

eventually pushing Buck1 to 100% duty cycle (Bypass

mode), the operational no-load quiescent current of the

MCP16502 shows some increase due to the

augmented switching activity of Buck1.

This is intrinsic to the Auto-PFM architecture. The

peaking in the quiescent current is in the 1 mA range,

and it may or may not be detrimental to the overall

system efficiency and/or battery life, depending mostly

on the minimum loading of Buck1.

If the increase in quiescent current when approaching

Bypass mode on Buck1 is an important factor for the

application, the user can optionally activate a different

mode of light load, high-efficiency operation (called

Hysteretic Control mode, HCM), where the output volt-

age is controlled in a hysteretic fashion between the

nominal output voltage and 2.9% of it. This is done by

setting the B1HCEN bit (Buck1 Hysteretic Control

Enable) in the SYS-CFG register through I2C. This

control method significantly reduces the average

switching activity of Buck1, especially in the proximity

of the bypass operation, at the expense of an increase

of the output ripple amplitude.

The user should therefore carefully evaluate the need

for activation of HCM for Buck1 and balance the

increase in output ripple against the real benefit

achieved in prolonging battery life. If the minimum

loading on Buck1 is always significantly higher than

1 mA, activation of HCM is typically not needed.

The relevant “Electrical Characteristics” parameter

that defines the upper voltage regulation threshold (typ-

ically +2.9% of the nominal output voltage) is the

Hysteretic Control Mode Upper Regulation Threshold.

Even if bit B1HCEN is set, HCM mode will only be acti-

vated when the input-to-output voltage differential

decreases below a certain value. This is done to pre-

vent fast inductor charging, which in turn may cause a

poorer control of the effective upper regulation voltage.

The relevant “Electrical Characteristics” parame-

ter that defines the input voltage threshold (falling input

voltage), below which HCM is enabled, is the Hyster-

etic Control Mode Enable Threshold and it is also

expressed as a percentage of the nominal output volt-

age value (typically, +9%).

5.5

Protections

The MCP16502 offers the following:

• Thermal Shutdown

• Thermal Warning

• Overcurrent Protection

Thermal Shutdown protection will immediately termi-

nate power delivery on all channels when the die

temperature exceeds the upper Thermal Shutdown

threshold. At the same time, nRSTO will be asserted

low. If the corresponding masking bit is cleared, nINTO

will also be asserted low.

After the die temperature has decreased below the

lower Thermal Shutdown threshold (hysteresis = 20°C)

and an additional 100 ms delay, the MCP16502 will

automatically attempt a new start-up sequence without

the need of an external Start condition (from nSTRT or

PWRLHD).

Thermal Warning does not invoke any automatic

action. If the die temperature exceeds the Thermal

Warning upper threshold, and if the corresponding

masking bit is cleared, it will only generate assertion

(LOW) of the nINTO output. The host MPU can then

interrogate the MCP16502 for diagnostic purposes.

5.5.1

OVERCURRENT PROTECTION

(BUCK CHANNELS)

The overcurrent protection consists of a cycle-by-cycle,

high-side current limit with digital filtering, followed by

the Hiccup mode for protection against short-circuit

conditions.

The cycle-by-cycle, high-side current limit includes

frequency foldback. Because of Leading-Edge Blank-

ing (LEB) in Peak Current mode control, frequency

foldback (with a factor = 4) is used to allow more time

for inductor discharge and prevent current runaway in

a deep overload condition.

Frequency foldback operation is entered when:

A high-side current limit event has been

detected; and

The feedback voltage is less than 500 mV

(typical).

Cycle-by-cycle overcurrent protection with frequency

foldback is always active and it is the first current limit

protection mechanism.

The second current limit mechanism is Hiccup mode

protection, which is also always enabled, including

during the soft start ramp and DVS transitions.

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