Micrel
MIC2586/MIC2586R
Pin Description
Pin Number
7
Pin Name
PGTIMER
Pin Function
Power-is-Good Delay Timer: A capacitor (C
PG
) connected from this pin to GND
sets a delay from PWRGD1 to PWRGD2 (t
PG(1-2)
) and from PWRGD1 to
PWRGD3 (t
PG(1-3)
). An internal current source (I
CPG
) is used to charge C
PG
only
after PWRGD1 has been asserted. The same description applies to the active-
LOW (-2) output signals.
Power-is-Good Output 3 (PWRGD3 or /PWRGD3), Open-drain Output: For the
(-1) option, this output signal is asserted when the following is true: PWRGD1 =
Asserted AND the PWRGD1-to-PWRGD3 delay (t
PG(1-3)
) has elapsed, where
t
PG(1-3)
is the time delay programmed by the capacitor (C
PG
) connected to the
PGTIMER pin. Once PWRGD1 is asserted, an internal current source (I
CPG
)
begins to charge C
PG
. When the voltage on C
PG
crosses the V
PG3
threshold
(typically, 1.25V), PWRGD3 is asserted. The same description above applies to
the (-2) option. For further information, refer to the PWRGD1 and PGTIMER pin
descriptions.
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 an internal pull-up impedance is provided by the dc-dc
module or other device (load).
Current Limit Response Timer: A capacitor connected from this pin to GND
provides overcurrent filtering to prevent nuisance “tripping” of the circuit breaker
by setting the time (t
FLT
) for which the controller is allowed to remain in current
limit. Once the MIC2586 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 (I
TIMERDN
). When the voltage across the external sense
resistor exceeds the V
TRIP
threshold, an internal 65µA current source (I
TIMERUP
) is
activated to charge the capacitor connected to the TIMER pin. When the TIMER
pin voltage reaches the V
TIMERH
threshold, the circuit breaker is tripped pulling
the GATE pin low, the I
TIMERUP
current source is disabled, and the TIMER pin
capacitor is discharged by the I
TIMERDN
current source. When the voltage at the
TIMER pin is less than 0.5V, the MIC2586 can be restarted by toggling the ON
pin LOW then HIGH.
For the MIC2586R, the capacitor connected to the TIMER pin sets the period of
auto-retry where the duty cycle is fixed at a nominal 5%.
11
GATE
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 (∆V
GATE
= V
GATE
- V
CC
) of +7.5V
over the input supply’s full operating range. When the ON pin voltage is higher
than the V
ONH
threshold, a 16µA current source (I
GATEON
) 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 V
TRIP
while the
capacitor connected to the TIMER pin charges. If the current limit condition goes
away before the TIMER pin voltage rises above the V
TIMERH
threshold, then
steady-state operation resumes.
The GATE output pin is shut down whenever: (1) the input supply voltage is
lower than the V
UVL
threshold, (2) the ON pin voltage is lower than the V
ONL
threshold, (3) the TIMER pin voltage is higher than the V
TIMERH
threshold, or (4)
the difference between the VCC and SENSE pins is greater than V
TRIP
while the
TIMER pin is grounded. For cases (3) and (4) – overcurrent fault conditions –
the GATE is immediately pulled to ground by I
GATEFLT
, a 30mA (minimum) pull-
down current.
9
PWRGD3
(MIC2586-1)
(MIC2586R-1)
Active-HIGH
/PWRGD3
(MIC2586-2)
(MIC2586R-2)
Active-LOW
10
TIMER
October 2004
4
M9999-102204
(408) 955-1690
MICREL [ MICREL SEMICONDUCTOR ]
