参数资料
| 型号： | ISL95870BIRZ |
| 厂商： | Intersil |
| 文件页数： | 16/28页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR PWM 1PHASE GPU 20QFN |
| 标准包装： | 75 |
| 应用： | 控制器，GPU 内核电源 |
| 输入电压： | 3.3 V ~ 25 V |
| 输出数： | 1 |
| 输出电压： | 0.5 V ~ 5 V |
| 工作温度： | -40°C ~ 100°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-VFQFN 裸露焊盘 |
| 供应商设备封装： | 20-QFN（3x4） |
| 包装： | 管件 |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页当前第16页第17页第18页第19页第20页第21页第22页第23页第24页第25页第26页第27页第28页
ISL95870, ISL95870A, ISL95870B
C SOFT = ---------------------------------------------------------------------
? R T ? LN ( 1 – ------------------------------ ) ?
which is written as:
? V START-UP ?
Where:
– t SS
? I SS ? R T ?
(EQ. 6)
Output Voltage Programming for ISL95870A
The ISL95870A allows the user to select four different reference
voltages, thus four different output voltages, by voltage
identification pins VID1 and VID0. The maximum reference voltage
cannot be designed higher than 1.5V. The implementation scheme
is shown in Figure 10. The setpoint reference voltages are
– t VS
C SOFT = ------------------------------------------------------------------------------
I VS ? R T
? R T ? LN ( 1 – --------------------------------------- ) ?
? R F ?
V SETX = V REF ? ? 1 + ---------- ?
- t SS is the soft-start delay
- I SS is the soft-start current source at the 17μA limit
- V START-UP is the setpoint reference voltage selected by the
state of the VID inputs at the time EN is asserted
- R T is the sum of the R SET programming resistors
Choosing the C SOFT capacitor to meet the requirements of a
particular voltage-step delay t VS is calculated with Equation 7,
which is written as:
(EQ. 7)
? V NEW – V OLD ?
? ?
Where:
- t VS is the voltage-step delay
- V NEW is the new setpoint voltage
- V OLD is the setpoint voltage that V NEW is changing from
- I VS is the ±85μA setpoint voltage-step current; positive
when V NEW > V OLD , negative when V NEW < V OLD
- R T is the sum of the R SET programming resistors
Output Voltage Programming for ISL95870
The ISL95870 has a fixed 0.5V reference voltage (V SREF ). As
shown in Figure 9, the output voltage is the reference voltage if
programmed with resistors that use the naming convention
R SET(x) where (x) is the first, second, or third programming resistor
connected in series starting at the SREF pin and ending at the GND
pin. As shown in Table 1, different combinations of VID1 and VID0
closes different switches and leaves other switches open. For
example, for the case of VID1 = 1 and VID0 = 0, switch SW1 closes
and all the other three switches SW0, SW2 and SW3 are open. For
one combination of VID1 and VID0, the internal switch connects
the inverting input of the V SET amplifier to a specific node among
the string of R SET programming resistors. All the resistors between
that node and the SREF pin serve as the feedback impedance R F
of the V SET amplifier. Likewise, all the resistors between that node
and the GND pin serve as the input impedance R IN of the V SET
amplifier. Equation 9 gives the general form of the gain equation
for the V SET amplifier:
(EQ. 9)
? R IN ?
Where:
- V REF is the 0.5V internal reference of the IC
- V SETx is the resulting setpoint reference voltage that
appears at the SREF pin
TABLE 1. ISL95870A VID TRUTH TABLE
VID STATE RESULT
R FB is shorted and R OFS is open. A resistor divider consisting of
R OFS and R FB allows the user to scale the output voltage
between 0.5V and 5V. The relation between the output voltage
and the reference voltage is given in Equation 8:
VID1
1
1
VID0
1
0
CLOSE
SW0
SW1
V SREF
V SET1
V SET2
V OUT
V OUT1
V OUT2
V OUT = V SREF ? ----------------------------------
R FB + R OFS
R OFS
(EQ. 8)
0
0
1
0
SW2
SW1, SW3
V SET3
V SET4
V OUT3
V OUT4
V OUT
R FB
FB
-
+
EA
V COMP
V REF
Equations 10, 11, 12 and 13 give the specific V SET equations for
the ISL95870A setpoint reference voltages.
The ISL95870A V SET1 setpoint is written as Equation 10:
(EQ. 10)
V SET1 = V REF
V SET2 = V REF ? ? 1 + -------------------------------------------- ?
V SET3 = V REF ? ? 1 + -------------------------------------------- ?
V SET4 = V REF ? ? 1 + ------------------ ?
+
V SET
-
SREF
FIGURE 9. ISL95870 VOLTAGE PROGRAMMING CIRCUIT
The ISL95870A V SET2 setpoint is written as Equation 11:
? R SET1 ?
? R SET2 + R SET3 ?
The ISL95870A V SET3 setpoint is written as Equation 12:
? R SET1 + R SET2 ?
? R SET3 ?
The ISL95870A V SET4 setpoint is written as Equation 13:
? R SET1 ?
? R SET2 ?
(EQ. 11)
(EQ. 12)
(EQ. 13)
The V SET1 is fixed at 0.5V because it corresponds to the closure
of internal switch SW0 that configures the V SET amplifier as a
16
FN6899.1
December 2, 2013
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