ISL68200 Datasheet, PDF (12/32 Pages) Intersil Corporation – Single-Phase R4 Digital Hybrid PWM Controller with Integrated Driver

ISL68200
Soft-Start
The ISL68200 based regulator has 4 periods during soft-start, as
shown in Figure 7 on page 12. After a 5.5ms timeout (worst
case = 6.5ms) of bias supplies, as shown in Figures 22 and 23 on
page 22, once the EN pin reaches above its enable threshold, the
controller begins the first soft-start ramp after a fixed soft-start
delay period of t_D1. The output voltage reaches the boot-up voltage
(V_BOOT) at a fixed slew rate in period t_D2. Then, the controller will
regulate the output voltage
SMBus/PMBus/ I²C sends
at V_BOOT for another period t_D3 until
a new V_OUT command. If the V_OUT
the
command is valid, the ISL68200 will initiate the ramp until the
voltage reaches the new V_OUT command voltage in period t_D4. The
soft-start time is the sum of the 4 periods, as shown in
Equation 1.
t_SS = t_D1 + t_D2 + t_D3 + t_D4
(EQ. 1)
t_D1 is a fixed delay with the typical value as 200µs. t_D3 is
vdoeltteargmeinfreodmbtyhtehSeMtimBuest/oPoMbBtauisn/Ia²Cnebwusv.aIlfidthVe^OV^UOTUc_T^{omcommamnadnd} is
valid before the output reaches the boot-up voltage, the output will
turn around to respond to the new V_OUT command code.
V_BOOT < PRECHARGED < OVP
V_BOOT
PRECHARGED < V_BOOT
V_OUT
0V
t_D1
t_D2
EN
t_D3 t_D4
PGOOD
FIGURE 7. SOFT-START WAVEFORMS
During t_D2 and t_D4, ISL68200 digitally controls the DAC voltage
change. The ramp time t_D2 and t_D4 can be calculated based on
Equations 2 and 3, once the slew rate is set by the PROG4 pin.
t_D2 = _{R-----A-----VM----}^B-P---^O--_--^O-R----^T_{A----T----E--} s
(EQ. 2)
t_D4 = ^V--_R---^O--_A--^U---_M-^T----_P-–----_{_}-^V--_R--^B--_A--^O--_T--^O--_E---^T- s
(EQ. 3)
The ISL68200 supports precharged start-up, it initiates the first
PWM pulse until the internal reference (DAC) reaches the
pre-charged level at RAMP_RATE, programmed by PROG4 or
D5[2:0]. When the precharged level is below V_BOOT, the output
walks up to the V_BOOT at RAMP_RATE and releases PGOOD at
t_D1 + t_D2, when the precharged output is above V_BOOT but below
OVP, it walks down to V_BOOT at RAMP_RATE and then releases
PGOOD at t_D1+t_D2, in which t_D2 is defined in Equation 4 and
longer than a normal start-up.
t_D2 = ^V----R-P---A-^R----^E_M----^C-P---^H--_--^A-R---^R--A--^G--T---^E_E----^D-- + ^V-----P----^R----^E----^C_R----^H-A---^A-M---^R---P-^G---_--^E-R---^D--A---^–-T---EV-----^B----^O----^O-----^T- s
(EQ. 4)
ISL68200 supports precharged load start-up up to the maximum
V_OUT of 5.5V with sufficient boot capacitor charge. For an
extended precharged load, the boot capacitor will be discharged
to “PVCC - V_OUT - V_D” by high-side drive circuits’ standby current.
For instance, an extended 4V precharged load, the boot capacitor
will reduce to a less than 1V boot capacitor voltage, which is
insufficient to power-up the VR. In this case, it is recommended
to let the output drop below 2.5V with an external bleed resistor
before issuing another soft-start command.
Boot-Up Voltage Programming
An 8-bit pin PROG1 is dedicated for the boot-up voltage
programmability, which offers 256 options 0V and 0.5V to 5.5V,
as in Table 7. The most popular boot-up voltage levels are placed
on the tie-low spots (0h, 20h, 40h, 60h, 80h, A0h, C0h, E0h) and
the tie-high spots (1Fh, 3Fh, 5Fh, 7Fh, 9Fh, BFh, DFh, FFh) for
easy programming, as summarized in Table 3. 0V boot-up
voltage is considered as “OFF,” the driver will be in tri-state and
the internal DAC will set to 0V.
In addition, if the VOUT_COMMAND (21h) is executed
successfully 5.5ms (typically, worst 6.5ms) after VCC POR and
prior to Enable, it will override the boot-up voltage set by the
PROG1 pin.
TABLE 7. PROG1 8-BIT (BOOT-UP VOLTAGE)
BINARY
CODE
V_BOOT
HEX CODE (V)
VOUT
COMMAND
CODE (HEX)
DELTA FROM
PREVIOUS
CODE (mV)
00000000
0
0.7969
66
00000001
1
0.5000
40
00000010
2
0.5078
41
7.8125
00000011
3
0.5156
42
7.8125
00000100
4
0.5234
43
7.8125
00000101
5
0.5313
44
7.8125
00000110
6
0.5391
45
7.8125
00000111
7
0.5469
46
7.8125
00001000
8
0.5547
47
7.8125
00001001
9
0.5625
48
7.8125
00001010
A
0.5703
49
7.8125
00001011
B
0.5781
4A
7.8125
00001100
C
0.5859
4B
7.8125
00001101
D
0.5938
4C
7.8125
00001110
E
0.6016
4D
7.8125
00001111
F
0.6094
4E
7.8125
00010000
10
0.6172
4F
7.8125
00010001
11
0.6250
50
7.8125
00010010
12
0.6328
51
7.8125
00010011
13
0.6406
52
7.8125
00010100
14
0.6484
53
7.8125
00010101
15
0.6563
54
7.8125
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March 7, 2016