MIC2584 Datasheet, PDF (20/28 Pages) Micrel Semiconductor – Dual-Channel Hot Swap Controller/Sequencer

MIC2584/2585
V_IN1
5V
V_IN2
3.3V
*D1
(8V)
*D2
(8V)
R1
33kΩ
R2
47kΩ
C5
0.01µF
R_SENSE1
0.012Ω
1 ^5% 2
Q1
IRF7822
(SO-8)
3
4
C1
1µF
R_SENSE2
0.012Ω
1 ^5% 2
Q2
IRF7822
(SO-8)
C2
1µF
24
VCC1
3
23
1
SENSE1 VCC2
8 _ON
11 _CFILTER
MIC2585-1
4
2
SENSE2
GATE2 ³
FB2 ⁷
5
OUT2
6
DIS2
R5
20.5kΩ
1%
C4
0.022µF
R6
8.66kΩ
1%
R9
3.6kΩ
R8
1.5kΩ
C7
0.033µF
C6
0.1µF
12 _CDLY
GND
13
Undervoltage (OUT1) = 4.4V
Undervoltage (OUT2) = 2.85V
Circuit Breaker Response Time = 5ms
Sequenced Output Delay (Turn-On) = 20ms
*Dual package Diode is AZ23C8V2
Resistors are 5% unless specified otherwise
Additional pins omitted for clarity
GATE1 ²²
DIS1 ¹⁹
OUT1 ²⁰
TRK
9
FB1 ¹⁸
R7
680Ω
C3
0.022µF
Figure 8. First On—Last Off Application Circuit
Micrel
C_LOAD1
220µF
V_OUT1
5V@2.5A
V_OUT2
3.3V@2.5A
C_LOAD2
220µF
R3
39.2kΩ
1%
Q3
ZTX788A
Q4
TCR22-4
R10
360Ω
R4
15.8kΩ
1%
Output Undervoltage Detection
For output undervoltage detection, the first consideration is to
establish the output voltage level that indicates “power is
good.” For this example, the output value for which a 12V
supply will signal “good” is 10.5V. Next, consider the toler-
ances of the input supply and FB threshold (V_FB). For this
example, given a 12V ±5% supply for Channel 1, the resulting
output voltage may be as low as 11.4V and as high as 12.6V.
Additionally, the FB1 threshold has ±50mV tolerance and
may be as low as 1.19V and as high as 1.29V. Thus, to
determine the values of the resistive divider network (R12
and R13) at the FB1 pin, shown in the typical application
circuit on page 1, use the following iterative design proce-
dure.
1) Choose R13 so as to limit the current through
the divider to approximately 100µA or less.
R13 ≅
V_FB1(MAX)
100µA
≅
1.29V
100µA
≅ 12.9kΩ_.
R13 is chosen as 14.7kΩ ± 1%.
2) Next, determine R12 using the output “good”
voltage of 10.5V and the following equation:
V_OUT1(Good)
=
V_FB1(MAX)



(R12 + R13)
R13



(10)
Using some basic algebra and simplifying Equation 10 to
isolate R12, yields:
R12
=

R13_{}
V_OUT1(Good)
V_FB1(MAX)




– 1^

(10.1)
where V_FB1(MAX) = 1.29V, V_OUT1(Good) = 10.5V, and R13 is
14.7kΩ. Substituting these values into Equation 10.1 now
yields R12 = 104.95kΩ. A standard 105kΩ ± 1% is selected.
Now, consider the 11.4V minimum output voltage, the lower
tolerance for R13 and higher tolerance for R12, 14.55kΩ and
106.05kΩ, respectively. With only 11.4V available, the voltage
sensed at the FB1 pin exceeds V_FB1(MAX), thus the /POR and
PG1 (MIC2585) signals will transition from LOW to HIGH,
indicating “power is good” given the worse case tolerances of
this example. A similar approach should be used for Channel 2.
MIC2584/2585
20
March 2005