参数资料
| 型号： | ISL95870BIRZ |
| 厂商： | Intersil |
| 文件页数： | 17/28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页第16页当前第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
R FB + R OFS
V OUT = V SREF ? ---------------------------------- = V SREF ? k
R
unity-gain voltage follower for the 0.5V voltage reference V REF .
Theoretically, V SET3 can be higher or lower or equal to V SET4
depending on the selection of R SET1 , R SET2 and R SET3 . However,
it is recommended to design the four reference voltages in the
following order:
- V SET1 < V SET2 < V SET3 < V SET4 Thus,
- V OUT1 < V OUT2 < V OUT3 < V OUT4
R OFS allows the user to program the output voltage in the range
of 1.5V to 5V. The relation between the output voltage and the
reference voltage is given in Equation 18:
(EQ. 18)
OFS
In this case, the four output voltages are equal to each of the
corresponding reference voltages multiplying the factor k.
For given four user selected reference voltages V SETx , the
following equation needs to be satisfied in order to have non-zero
V OUTx = V SETx ? k
(EQ. 19)
solution for R SETx .
V SET1 ? V SET2 + V
SET3
? V SET4 – V SET2 ? V SET3 – V SET2 ? V SET4 = 0
Output Voltage Programming for ISL95870B
The ISL95870B allows the user to select four different reference
R SET3 ? ( V SET4 – V REF ) ? ( V SET2 – V REF )
R SET1 = ---------------------------------------------------------------------------------------------------------------------
V REF ? ( V SET4 – V SET2 )
R SET3 ? ( V SET2 – V REF )
R SET2 = --------------------------------------------------------------------
(EQ. 14)
The programmed resistors R SET1 , R SET2 and R SET3 are designed
in the following way. First, assign an initial value to R SET3 of
approximately 100k Ω then calculate R SET1 and R SET2 using
Equations 15 and 16 respectively.
(EQ. 15)
(EQ. 16)
V SET4 – V SET2
The sum of all the programming resistors should be
approximately 300k Ω, as shown in Equation 17, otherwise adjust
the value of R SET3 and repeat the calculations.
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 11. The setpoint
reference voltages are programmed with resistors that use the
naming convention R SET(x) where (x) is the first, second, third, or
fourth programming resistor connected in series starting at the
SREF pin and ending at the GND pin. As shown in Table 2,
different combinations of VID1 and VID0 close different switches
and leave 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
R SET1 + R SET2 + R SET3 ? 300k Ω
(EQ. 17)
the SREF pin serve as the feedback impedance R F of the V SET
amplifier. Likewise, all the resistors between that node and the
V SETX = V REF ? ? 1 + ---------- ?
VOUT
RFB
FB
-
+
EA
VCOMP
GND pin serve as the input impedance R IN of the V SET amplifier.
Equation 20 gives the general form of the gain equation for the
V SET amplifier:
? R F ?
(EQ. 20)
? R IN ?
+
V SET
-
VREF
0.5V
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
SREF
SW0
TABLE 2. ISL95870B VID TRUTH TABLE
VID STATE
RESULT
SET0
SET1
SW1
SW2
VID1
1
1
0
0
VID0
1
0
1
0
CLOSE
SW0
SW1
SW2
SW3
V SREF
V SET1
V SET2
V SET3
V SET4
V OUT
V OUT1
V OUT2
V OUT3
V OUT4
SW3
Equations 21, 22, 23 and 24 give the specific V SET equations for
the ISL95870B setpoint reference voltages.
The ISL95870B V SET1 setpoint is written as Equation 21:
V SET2 = V REF ? ? ?
FIGURE 10. ISL95870A VOLTAGE PROGRAMMING CIRCUIT
If the output voltage is in the range of 0.5V to 1.5V, the external
resistor-divider is not necessary. The output voltage is equal to
one of the reference voltages depending on the status of VID1
and VID0. The external resistor divider consisting of R FB and
V SET1 = V REF
The ISL95870B V SET2 setpoint is written as Equation 22:
? R SET1 ?
1 + ---------------------------------------------------------------------
? R SET2 + R SET3 + R SET4 ?
(EQ. 21)
(EQ. 22)
17
FN6899.1
December 2, 2013
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