MIC2587R-1YM(2013) Ver la hoja de datos (PDF) - Micrel
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MIC2587R-1YM Datasheet PDF : 22 Pages
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Micrel, Inc.
MIC2587/MIC2587R
Pin Description (Continued)
Pin Number
3
4
5
6
Pin Name
PWRGD
(MIC2587-1)
(MIC2587R-1)
Active-HIGH
/PWRGD
(MIC2587-2)
(MIC2587R-2)
Active-LOW
GND
TIMER
GATE
Pin Function
Power-is-Good (PWRGD or /PWRGD), Open-Drain Output: This pin remains de-asserted during
start up while the FB pin voltage is below the VFBH threshold. Once the voltage at the FB pin
rises above the VFBH threshold, the Power-is-Good output asserts with minimal delay
(typically ≤ 5µs).
For the (−1) options, the PWRGD output pin will be high-impedance when the FB pin voltage is
higher than VFBH and will pull down to GND when the FB pin voltage is less than VFBL.
For the (−2) options, the /PWRGD output pin will be high-impedance when the FB pin voltage is
lower than VFBL and will pull down to GND when the FB pin voltage is higher than VFBH.
The Power-is-Good output pin is connected to an open-drain, N-channel transistor implemented
with high-voltage structures. These transistors are capable of operating with pull-up resistors to
supply voltages as high as 100V.
To use this signal as a logic control in low-voltage DC/DC conversion applications, an external
pull-up resistor between this pin and the logic supply voltage is recommended unless the DC/DC
module or other load is equipped with a internal pull-up impedance.
Tie this pin directly to the system’s analog GND plane.
Current-Limit Response Timer: A capacitor connected from this pin to GND sets the time (tFLT)
for which the controller is allowed to remain in current limit before “tripping” the circuit breaker.
The overcurrent filter is designed to prevent nuisance “tripping” of the circuit breaker that can be
caused by transient current spikes or other undesired “noise”. Once the MIC2587 circuit breaker
trips, the output latches off. Under normal (steady-state) operation, the TIMER pin is held to
GND by an internal 3.5µA current source (ITIMERDN). When the voltage across the external sense
resistor exceeds the VTRIP threshold, an internal 65µA current source (ITIMERUP) is activated to
charge the capacitor connected to the TIMER pin. When the TIMER pin voltage reaches the
VTIMERH threshold, the circuit breaker is tripped pulling the GATE pin low, the ITIMERUP current
source is disabled, and the TIMER pin capacitor is discharged by the ITIMERDN current source.
When the voltage at the TIMER pin is less than 0.5V, the MIC2587 can be restarted by toggling
the ON pin LOW then HIGH.
For the MIC2587R, the GATE output attempts another start cycle to re-establish the output
voltage when the circuit breaker is tripped upon an overcurrent fault. The capacitor connected to
the TIMER pin sets the period of auto-retry with a fixed, nominal duty cycle of 5%.
Gate Drive Output: This pin is the output of an internal charge pump connected to the gate of an
external, N-channel power MOSFET. The charge pump has been designed to provide a
minimum gate drive (∆VGATE = VGATE − VCC) of +7.5V over the input supply’s full operating range.
When the ON pin voltage is higher than the VONH threshold, a 16µA current source (IGATEON)
charges the GATE pin.
When in current limit, the output voltage at the GATE pin is adjusted so that the voltage across
the external sense resistor is held equal to VTRIP while the capacitor connected to the TIMER pin
charges. If the current limit condition goes away before the TIMER pin voltage rises above the
VTIMERH threshold, then steady-state operation resumes.
The GATE output pin is shut down whenever: (1) the input supply voltage is lower than the VUVL
threshold, (2) the ON pin voltage is lower than the VONL threshold, (3) the TIMER pin voltage is
higher than the VTIMERH threshold, or (4) the difference between the VCC and SENSE pins is
greater than VTRIP while the TIMER pin is grounded. For cases (3) and (4) – overcurrent fault
conditions – the GATE is immediately pulled to ground by IGATEFLT, an 80mA pull-down current
source.
January 24, 2013
4
Revision 2.0
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