Micrel
MIC2587/MIC2587R
Pin Description
Pin Number
Pin Name
Pin Function
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.
Circuit Breaker Sense Input: This pin is the (-) Kelvin sense connection for the output
supply rail. A low-valued resistor (R
SENSE
) between this pin and the VCC pin sets the circuit
breaker’s current limit trip point. When the current limit detector circuit is enabled (as well as
the current limit timer), while the FB pin voltage remains higher than 1V, the voltage across
the sense resistor (V
CC
-V
SENSE
) will be regulated to V
TRIP
(47mV, typically) to maintain a
constant current into the load. When the FB pin voltage is less than
≅0.5V,
the voltage
across the sense resistor decreases linearly to a minimum of 12mV (typical) when the FB
pin voltage is at 0V.
To disable the circuit breaker (and defeat all current limit protections), the SENSE pin and
the VCC pin can be tied together.
Positive Supply Voltage Input: This pin is the (+) Kelvin sense connection for the output
supply rail. The nominal operating voltage range for the MIC2587 and the MIC2587R is
+10V to +80V, and VCC can withstand input transients up to +100V. An undervoltage
lockout circuit holds the GATE pin low whenever the supply voltage to the MIC2587 and the
MIC2587R is less than the V
UVH
threshold.
6
GATE
7
SENSE
8
VCC
October 2004
4
M9999-102204
(408) 955-1690
MICREL [ MICREL SEMICONDUCTOR ]
