The MAX15162/MAX15162A are 8V to 60V integrated, dual-channel circuit breaker devices. The dual channels can be configured as independent mode, or parallel mode to scale up the current capability. The devices feature constant power control during startup process to ensure MOSFETs operating under Safe Operating Area (SOA). The programmable current limit and adjustable shutdown time for current limit event provide flexibility for various applications with different power levels. The fast overcurrent protection can shut down the MOSFET within 200ns when a larger current or short-circuit occurs at the output. The ±3% current monitoring over the input and temperature change can provide accurate current information to the system. The ALRT response indicates the output and fault status, and it asserts when
The output is disabled
Current limit occurs
Overtemperature occurs
Startup watchdog times out
Configuration fault occurs.
The active-high EN pin functions make enable/disable easy to control. The input and EN debounce protection prevent the MOSFET turning on from noisy or transitioning input or EN signals. The IN-to-OUT short-circuit protection prevents the MOSFET from turning on when the MOSFET is shorted or the input and output are in shorted condition. The devices provide a choice of auto-retry or latch-off mode during fault events based on MAX15162A or MAX15162.
Startup
The devices are designed to power-up the output with constant power control by actively monitoring the MOSFET power and limiting the startup current. The startup current is a series of pulsating current whose duty cycles are controlled by constant power limit circuit. The averaged startup current with constant power control is approximately 28mA. This scheme is to ensure the internal MOSFET operate within SOA during the startup. Once the output ramps up to be within 700mV of the input voltage, the MOSFET is switched to constant current control to expedite the startup process. When the MOSFET is fully turned on, the current limit is switched to programmable normal operation current limit threshold.
An internal watchdog timer starts counting when the devices enter the startup phase. The devices complete the startup phase, de-assert ALRT pin and enter normal operation mode once VIN - VOUT < 700mV. If the watchdog timer elapses and VIN - VOUT is still greater than 700mV, the MOSFET will be turned off and the devices enter auto-retry mode in the MAX15162A or latch mode in the MAX15162. When the auto-retry time elapses the part will restart the power-up process. The thermal-protection circuit is always active and the MOSFET will be immediately turned off when the thermal-shutdown threshold is reached.
Startup in Overload or Short-Circuit Condition
When the device powers up the MOSFET with a very large load or short circuit at the output, the duty cycles of the pulsating startup current is limited to initial values to ensure the power dissipation is not overheating the device . While the output is shorted to GND, the MOSFET will be turned off once the startup watchdog timer times out in 250ms. The device then restarts the power-up process in auto-retry mode (MAX15162A), or latches off the MOSFET until EN is toggled or the input is cycled to cross UVLO (MAX15162).
Undervoltage Lockout (UVLO)
The devices feature an undervoltage lockout functionality. When the input voltage falls below VUVLO the internal MOSFET is turned off immediately and ALRT pin asserts to indicate the fault condition. The UVLO comparator has a hysteresis of 500mV (typ).
Input Debounce Protection
The devices feature an input debounce protection in startup process to prevent the MOSFET from turning on from noisy and transitioning input. The devices start to ramp up the output (turn on the internal MOSFETs) only when the input voltage is higher than UVLO threshold and EN is pulled high for a period that is greater than the debounce time (TDEB). The TDEB time elapses only at startup process.
Figure 1. Input Debounce Protection
Enable
The dual MOSFETs can be individually enabled or disabled through EN_ pin by externally driving it above or below the EN_ threshold voltage. To enable the device EN_ pins must be pulled up to at least 1.4V or left floating. The external driving voltage can be as high as 5V. EN_ pins are default active-high with internal 2V pullup circuit, even when they are floated. The EN pins also have debounce protection to prevent the MOSFET from turning on by noise glitches on EN_ pins. If the device is configured to be parallel mode, two EN pins are required to tie together externally. When both EN_ pins are pulled to below 0.4V, externally the device shutdown current reduces to 32µA in low current shutdown mode.
IN-to-OUT Short-Circuit Protection
At startup, after the MOSFET is enabled without any faults, the device immediately checks for an IN-to-OUT short-circuit fault. If VIN - VOUT is less than a threshold (700mV), the internal MOSFET turns off and the device enters latch off mode (MAX15162) or auto-retry mode (MAX15162A). This is to prevent the MOSFET from turning on in shorted VIN to VOUT or shorted MOSFET condition.
Overcurrent and Short-Circuit Protection
Overcurrent fault protection is enabled in normal operation after the startup process with comparators for normal current limit threshold and fast current limit threshold. Overcurrent limit level can be configured through IMON_ pins for each MOSFET. The current limit comparator is designed so the load current can exceed the threshold for a programmable delay time prior to shut down the MOSFET. The delay time can be configured through DLY pin by connecting a resistor to GND (see Table 3).
During an overcurrent event, the ALRT pin asserts once the current limit threshold is tripped. The device turns off the internal MOSFET and disconnects the output from the input once the delay time elapses (see Figure 2). The device then operates in either auto-retry mode and restarts the output after a TRETRY delay elapses (MAX15162A) or enters latch mode and latches off the output until EN is re-enabled or the input is cycled to cross UVLO threshold (MAX15162).
The devices also feature catastrophic fast overcurrent protection for large load event or short circuit condition. During normal operation, if the output is shorted to the ground or a very large current with high slope rate (di/dt) occurs, once the current reaches fast current limit comparator threshold (133% of normal current limit), a fast protection circuit forces the gate of the MOSFET to discharge rapidly and disconnect the output from the input in 200ns (see Figure 3).
Figure 2. Overcurrent Event
Figure 3. Fast Overcurrent Event
Current-Limit Threshold and Current Monitor (IMON_)
Connect a resistor between IMON_ and GND to program the current limit thresholds of the devices. Use the following equation to calculate current limit setting resistor RIMON_ for independent mode:
RIMON_ (Ω) = 1.125 x CIRATIO/ILIM (A)
In parallel mode, connect IMON1 and IMON2 pins together with one resistor to GND, and use the following equation to calculate current limit setting resistor RIMON_:
RIMON_ (Ω) = 1.125 x CIRATIO/ILIM (A)/2
Where ILIM is the desired current limit in A, and CIRATIO is current sensing ratio (4000, typ). Table 1 and Table 2 show RIMON_ resistor settings for normal overcurrent limits and fast overcurrent limits for in independent and parallel mode respectively.
Table 1. RIMON Settings for Overcurrent Limit in Independent Mode
RIMON_ (KΩ)
IN INDEPENDENT MODE
CURRENT LIMIT/CHANNEL (A)
FAST OCP LIMIT/CHANNEL (A)
9.09
0.50
0.66
6.04
0.75
0.99
4.53
0.99
1.32
3.01
1.50
1.99
Table 2. RIMON Settings for Overcurrent Limit in Parallel Mode
RIMON_ (KΩ)
IN PARALLEL MODE
CURRENT LIMIT/ CHANNEL (A)
FAST OCP LIMIT/CHANNEL (A)
4.53
0.50
0.66
3.01
0.75
1.00
2.26
1.00
1.33
1.50
1.50
2.00
The devices feature a precise analog read-out of the current. The mirrored current flows out through IMON_ pins into external current-limit resistor RIMON. The voltage on IMON_ pin VIMON provides information about the current with the following relationship:
IOUT (A) = VIMON (V) x CIRATIO/RIMON(Ω)
In independent mode, IOUT in above equation represents the current from individual channel. In parallel mode, while connect IMON1 and IMON2 pins together, IOUT represents the summed current of two channels.
IMON_ pins must not be left floating.
Overcurrent Response and Shutdown Delay (DLY)
When the current flowing through the MOSFET reaches current limit threshold, TDELAY timer begins to count up, and ALRT pin is asserted. If the current drops back to below current limit threshold then the TDELAY timer begins to count down, as shown in Figure 4. The timer counting-down speed is slower than counting-up speed. Once the configured TDELAY time is reached by the timer, the MOSFET is turned off. This mechanism is to prevent the MOSFET from turning off due to high-frequency current ripples or noises through the device.
Figure 4. Overcurrent Response and Shutdown Delay
In the MAX15162A, in an overcurrent event, a auto-retry time delay (TRETRY) starts immediately after TDELAY elapses. During TRETRY time the MOSFET remains off. Once TRETRY elapses the MOSFET is turned on again. If the fault still exists then the cycle is repeated and ALRT pin remains asserted. If the overcurrent condition is resolved within TDELAY, the switch stays on. By connecting a resistor to GND on DLY pin to set TDELAY time and TRETRY time, as shown in Table 3:
Table 3. RDLY Settings for Delay Time and Auto-Retry Time—MAX15162A
RDLY (KΩ)
DELAY TIME TDELAY
AUTO-RETRY TIME TRETRY (ms)
0
12μs
0.6
28
100μs
6
47.5
1ms
60
68.1
10ms
600
In the MAX15162, in an overcurrent event after TDELAY elapses, the MOSFET is turned off and enters latch off mode until EN pin is re-enabled or the input is cycled to cross UVLO.
ALRT_ Response
The devices feature an open-drain, ALRT_ output as indication of MOSFET fully turning on and fault events. Once the MOSFET is fully enhanced without any faults ALERT_ pin will be de-asserted and remain de-asserted in MOSFET normal operation. ALERT_ pin will be asserted when
MOSFET VDS voltage is greater than 2V.
Input voltage drops to UVLO level.
Overcurrent limit threshold is tripped.
Overtemperature threshold is tripped.
Startup watchdog timer times out.
Startup configuration fault occurs.
In Parallel mode, ALERT_ pins are driven by status of both MOSFETs. Fault from either channel will assert both ALERT_ pins.
Independent and Parallel Mode
The devices can be configured as two independent channels or parallel channels for one common output. The device is configured as independent mode if IMON_pins are separately connecting to two resistors. To configure as parallel mode, two IMON_ pins are required to tie together and connect to one resistor across IMON_ to GND, EN1 and EN2 pins are required to tie together, and OUT1 and OUT2 are to be connected together. The device detects IMON_ pins connection during initialization process and determines independent or parallel channel configuration mode. IMON_ pins must not be left floating; otherwise, a startup configuration fault occurs.
Fault Auto-Retry and Latch Off
In a fault condition, the MAX15162A supports auto-retry mode and the MAX15162 supports latch-off mode. When the device turns off the MOSFET due to below fault conditions:
Overcurrent event after delay time elapses.
Fast overcurrent threshold is tripped.
Output hard short event.
Startup watchdog timer times out.
After the MOSFET is turned off, the MAX15162A enters auto-retry mode and restarts the power-up process after auto-retry delay time elapses. If the power-up is not successful in 250ms watchdog timeout, it stops and waits till the delay time elapses and starts next power-up. The auto-retry attempts totally 3 times. After three time auto-retries if the power-up is still not successfully the device stops retrying and latches off. In auto-retry mode, the delay time is configured by DLY pin.
The MAX15162 enters latch off mode once the fault events occur and the MOSFET is turned off, and it restarts the power-up process once EN_ is re-enabled or the input is cycled to cross UVLO.
Thermal Protection
The devices enter a thermal-shutdown mode in the event of overheating caused by excessive power dissipation or high ambient temperature. When the junction temperature exceeds thermal shutdown threshold, the internal thermal- protection circuitry turns off the MOSFET and ALRT_ asserts to indicate the fault event. When the junction temperature falls below thermal-shutdown threshold hysteresis level, the device restarts the MOSFET power-up process.
