-13-
超低压差线性稳压控制器 MIC5刂 “51夕 /s158
ˉ :控
拄低在 差残性稳 珏 制 器 MIC5“ 乃157/5158
●新 特 器 件 应 用
|
、
通信指挥学院
∷
钟利 平
|
刘成 芳
摘 要 :MIC51茹 冫5Ⅱ ″ 51ss系 列超 低 压 差 线 性 稳 压 控 制 器 可 使 稳 压 器输 入 输 出 电压 差 特
别低 ,外 部 元件 很 少 ,应 用 范 围很 广 。∶本 文 介 绍 了该 系列 器件 的 结 构 、特 `点 和 管脚 功 能 ,详
∷
细 地 /,x析 了 工 作 原 理 -并 给 出 了女 痴 电路 。
・
关键词:低 压差 线枉瘾压架 后盅癔压器
∵
工 种 固定 电压 稳 压控 制器 ,输 出电压 分别 为
1.概 述
3.3V,5.0V或 ⒓V。 MIC51sB可 以组成输 出
电压为 5V的 稳压器 ,同 时 ,利 用两只外接电
阻 将 MIC51ss组 成的稳压器输 出电压可从
1,3V调 整到 %V。
∶
MIC51“ /557/51ss主 要用于大电流低
压差线性稳压电j源 中。
`为 了输1出 棘末 B0电 流
应外接 N沟 道功率 MOSFET作 为线性串联调
ˇ
整元件。
,
・
,
,∷
主要特点如下
● 工作电流 :4。 smA;
:
MIC51“ /51夕/51ss组 成 的稳 压 器输 人
◆
●静态电流∵般小于 1uA;
●外部元件数很少
● 限流值可选 (工 般 门限是 “mV);
●MIC51“ 输 出电压恒定 :3.3V`5,0V;
MOsmT妁 导 通 电 阻
RDs(c,N)与 输出电流的乘积:最 太输出电流由
MOSFET的 额定吧流决定。
~
输 出 电压 差 等 于 外 接
:
MIC51“ /5157/5158系 列控制器 的工作
电压范围为直流 3V至 %V。 MIC51“ 需要较
高的栅极驱动电压,以 便驱动外接 M0sFET。
为此,MIC51夕 和 MIC51“ 都有一个三倍压
充电泵电路,以 便产生栅极驱动电压 接 3.5V
:∶
电源时,充 电泵电路可驱动 :MOsFET使 之输
出电压为 3.3V,同 时它还可将输出电压箝位在
高于电源电压的 n9.5V。 三倍压 电路薷要三只
外接电容器。
该控制器 外接取样 电阻 的两端龟 压 为
5mV时 ,稳 压器输出电流恒定。开路集电极输
出,低 电平时 FLAG脚 指示输 出电压低于额定
8%。 与 TTL兼 容的关断信号(低 电平)可
值的∴
使该控制器的电流降至 lltA,从而使锢 出电压
∷
∵
∵
降为零。
MI()51“ -3.3和 MIC51“ |5.0控 制 器
:
内部 具 有 固 定 的 输 出 电压 。 外 接 两 个 电 阻
,
MIC51“ 的输 出 电压 可 以 调 整 。 MIC51W是
;
Ⅱ
●MIC5157输 出电压恒定:3,3V、
12V;
5.0V、
′
● MIC51∞ /51ss外 接 二 个 电阻输 出电压
可在 1.3V到 “ V之 间调整
;
● Enable(使 能 )脚 可导通 /关 断稳压 器
● 元 件 内部 有 栅 极 一 源 极 箝 位 保 护 电路
;
,
如 图 1所 示 。
2.最 大额定值 ∶
MIC51“ /51乡/51狁 系列最大 额定值 如
下
:
●⒕ D∶ 38V;
● EN:ˉ 0.3≈ 36V;
、
∵
●%(MIC51“ ):ssV∵
●VtP(MIC51夕 /B):“ V;
3~36V;
●V源 极△・
●FLAG:ˉ 0.3~硐 V;
:电
源专辑
199⒏ 午第 9期 ∷1g98年 0月
《国外电子元器件》
4.1MIC51狁 管脚功能
●工作结温 TJ△ sO℃
∷
●贮存温度△ˉ甾 t1sO℃ ;∷
;∵∷
-14-
l
晶瑞扩
;
・焊接温度(1汛 ):sO0℃ ;
'
3.管 脚封装
^
∷
5isg系
,lj管 踟葑嚷如囱
血l己 si宽 /sls″
=
'
:
∶∷
所示,管 脚封装参数如表 1所 列。
表
∶∶
|∵
|‘
醐 畿茹
1 MIC51“ /5157/8管 脚封装
卜亡
4.管 脚 功 能
°,1uF∶
02
"01 0.1uE II亠
C1+IC1-IC2+l(冫 卜 l Vcρ
图1
ME51sT方 框原理图
啷
X
,
口
V。 。
s(souⅡ →
D(0mlol∷
G(GaloJ
∝弘
V。
β(Gatel
GND‰
cND%
G(G:l!ol
(Df。 in)
GNDvP
D(Drah)
E^
≡
s(sourool
EN啷
EN咖
"IC516⒍
EN
V。
。
C1C1△
∶
泓
‰∝弘
瓿⑾
帅
∷
〓
w.哪
X。
.
图2
M眵 51“ /T/8系 列管脚封装图
EN
s(sourco)
0(Dfa")
C〈 od。 J∶
V。 。
C1C1+
超低 压 差线性稳 压 控 制 器 MIC51甾 /s157/51sg
∶∴ Ⅱ
时,关 断稳压器。 ∷
∶
FLAG(脚 :z,:输 出端:当 .%uT∷ 电压降低的
:
数值超过额定值 8%时 ,开 路集 电极输 出低电
∷
平,该 电路有 3%的 滞后。
‘
GND觯 F3):地 。
%(脚 4):N沟 遣栅极驱动电源电压,可 驱
¨ ′
动外部 M0SFET的 栅极。 'Ⅱ
∷∷
%。 (脚 5):电 源电压输入脚。若需要限流
该脚应接在取样电阻 Rs和 ‰ 脚之间。同时
∶
该脚到地之间还应接人旁路电容。
G(脚 ω∵栅极 (G。 te)驱 动输出脚。可驱动
∵ ∶
.∴ j ∶∷ ∶
外部 MOsFEt的 栅极。
i
,
,
D(脚 7):漏 极(Drai0利 .限 流输人脚j需 要
限流时,该 脚应接 MOsFET漏 极和外部取样
电阻(限 流 ),不 需要限流时,该 脚应接在 %D和
∶
∷
外接 MOSFET的 漏极。∴
S(脚 8:3,3V,5V):源 极(输 人脚 )。 内部串
联分压电阻的顶端,为 F更 好地稳压,该 脚可直
’
接接负载。
EA(脚 8:可 调 ):误 差放大器输人脚。接外
∴
Ⅱ ∴Ⅱ
部电阻分压器。
4.2MIC51夕 、MIC51ss管 脚 功 能
5Ⅴ (MIC5157脚 1):输 出 5V电 压时,该
脚应接 M0sFET的 源极 (S脚 )。 ⅡⅡ ∷
EA(MIC51ss脚 1):误 差放大器输人脚
外接电阻分压器,可 调节输由电压。
3∶ 3ˇ (M℃ 51sT脚 0:输 出 ⒊3V电 压
Ⅱ∷
∵ ∶
时,该 脚应接源极(S脚 )。
5V FB(MIC51sB脚 V:钾 反馈电压输入
(脚
EA脚 ,可 输出 5V电 压。 ∷
。该脚接∵
FLAG(脚 ω :输 出电压指示 (输 出脚),当
V。 uT屯 压低于额定值的 8%时 ,开 路集电极输
-
出低电平。
:
′
.
∶i
ⅡⅢ
∶
(脚
:三 倍压充电泵输出脚 (滤 波电
⒒”
′ 分
容器)。 该脚到地之间应接ˉ个 lltF≈ lOuF的
∵
∷
电容。
GND(脚
4):地 。
C2亠 (脚 6):充 电泵电容∷
C2,∵ 内部三倍压
-15亠
电路的第二级。C2+与 C2△ 之间应接人 0,lf.F
电容 。
C2+(脚 V:充 电泵电容 ∞ ,见 脚 6的 功
能。
∷
C1+(脚 g9:充 电泵电容 CL内 部三倍压
电路的第一级,C1+与 C1-之 间应接人 炜F
0∶
电容。
∷ ∷
・
C1-(脚 9):充 电泵电容 C1,见 脚 8的 功
∶ ∴
∶{ ∷ ∶ j
能。∶
VDD(脚 IO):电 源电压输人脚。若 电路中有
限流电阻,该 脚应接取样电阻 Rs和 :‰ 脚。同
时,该 脚到地之间还应接旁路电容。
Ⅱ G(脚 :11):MOSFET栅 极输出脚。该脚接
∷
i
外部 MOSFET栅 极。
D(脚 1z):MOsFET漏 极和限流电路输人
脚。电路中有限流电阻时,该 脚接 MOSFET漏
极和外部取样电阻 ;电 路申没有限流电阻时,该
￠
脚接 VDD和 外部 MOsFET的 漏极。 ∷
S(MIC5157脚 1s):该 脚接内部串联电阻
顶端和外部 MOSFET的 源极 ,可 输 出 3.3Ⅴ 、
∶
W和 lzV稳 定电压。
S(MICs1ss脚 13):该 脚接内部串联电阻
顶端 、外部分压 电阻和外 部 Mα FET的 源
∷
∶
极。
EN(脚 14):使 能输人脚。该脚输人 TTL
L低 电平
高电平时,稳 压器正常工作 ;输 人
时,稳 压器关断。
5.工 作原 理
"Γ
∷
、
5.1MICs15“ 515T/s158规 格说明
MIC51“ 需要 用外部 电压来 驱 动 Mo⒏
mT。 它有输 出电压为 3.3V、 5V和 可调三种
∷
规格。
∴MIC51夕 和 MIC515g内 部都有三倍压充
电泵电路 ,该 电路可给 MOsFET提 供栅极驱
动电压。MIC51夕 有输 出电压为 ⒊3V(5V和
12V三 种规格。MIC51狁 有输 出 5V恒 定电压
和输出电压可调两种规格。
-16-
《国外电子元器件》1998年 第9期 ∷199B年 9月 :/电 源专辑
5.2Enable(EN)使 能脚
:
∶
%D脚 电压高于 3.0V且 使能脚 (EN)为
TTL低 电平时,控 制器关断。使能脚 (EN)为
TTL高 电平时,内 部偏压 电路为整个内部电路
供电。EN脚 悬空时 ,电 平可拉高到 %V。 在关
断状态下 ,该 控制器的输人 电流只有 △A。 ∷
5.3栅 极增强电压
超 低压差线性稳压控制器可以控制电源和
负载之间的 N沟 道 MOSFET(串 联调整元件 )
的i栅 极△ 源极增强电压
据电源电压和负载
^根
不同J栅 ÷源电压应‘
OV之 间。
∷∷
在△△ 邑
当稳压器工作在低压差状态时,由 于源极
电压 (即 输 出电压 )与 漏极电压非常接近,就 需
要更高的电压来驱动栅极。MIC51“ 这个更高
的 栅 极 驱I动 电 压 由 外 部 驱 动 电 源 提 供 。
MIC51sT和 MIC5158则 油内部充电泵提供。
⒌4栅 极驱动电源电压 (仅 限于 MIC51“ )
栅极驱动电压不能高于 ⒕V,即 VPˉ %D
驱动电压最小值-由 下式给:出 Ⅱ∶ ・
VI,△ ˇ
∷ ・
。iΠ `十 Vls+1
式中,Vl,是 栅极驱动电源电压 ;Vr)uT是 稳
压器输出电压∷Vtis是 栅极 一源极 电压。
∫ 误差放大器利用栅极驱动电源电压来驱动
<1z】 V。
放 大 器 输 出 可 在 V口 ± 1V内 变 化 。∶
虽然
MIC5157/51Ss曲 内部充 电泵产生 驱动 电压
的,但 是外接栅极驱动电压也可加到Ⅱ
杨 脚。此
∷
时,VtP不 能比 VI,D高 ⒕V以 上 。
负载恒定时,充 电泵导通和关断的转换波
形十分规则。该:波 形 的周期 由下 列 因素决定
输人电压 、lmA运 算放大器负载 电流 、Mo⒊
FET栅 极漏电流、产
充电泵贮能 电容值及输人 电
压和 负载的特性 等。增大充 电泵贮能电容 C3
:
的容量,周 期将增 汽 电容 C1和 C2∶ 的容量决
定波形的振幅σ・
应用时,如 果脉 冲窄,贮 能电容
C3可 选 用 10uF电 容器:∶ rc】 租 ∞ 可选 用
0.01uF电 容器。应 当注意 ,充 电泵电容的容量
过小 时 ,可 重复 负载:瞬 变的恢复时间将:受 影
●∶, Ⅱi
日
∷
i l∶ Ⅱ
向。 ∷ Ⅱ
5.6栅 极 一源极电压箝位 ∴ Ⅲ
M(BFET的 栅极… 源极 ⒗。6V∶ 箝位 电压
ˉ
可 防 止 因输 出 电压 突 变 到 零、
而 损 坏,Mo⒊
FET。 (注 :MIC51“ 输出电压可调规格中没有
箝位电压。 )
:
.
5.7输 出稳压电路
起动时,误 差放大器反馈 电压 (EA》 或内部
外部 M(DSFET的 栅极。误差放大器的输 出电
1V内 变化占|∷
压 叮在 .⒕ ±、
5,5充 电泵电路 (汉限于 M℃ 51贸/51s8)
反馈 电压 (输 出固定定型 )与 内部 1.⒛ 5V带 隙
基准电压 比较。若输 出电压低于额定值 ,误 差
放大 器输 出 电压 升 高并使外部 MOSFET Q1
导通。然后 ,控 制器根据反馈 电压 ,调 整误差放
三 倍压充 电泵电路在贮能电容 C3两 端产
大器输 出电压 ,调 节输人电压和负载 ,使 稳压器
生直流电压。 外部电容 C1和 c?给
压充
电泵提供所需的贮肓
=倍
⒏)三 倍 压充电泵直流输出
△ ,Ⅲ ∶
∷
电压为:
.Vr・P≈ 3(V】 丬
,-1)
输 出电压保持恒定。
5,⒏ 电压过低 检测
Ⅱ
当输 出电压 比额定 值 低 8%或 更低时、开
路集 电极 F△ AG脚 输 出低 电平并发 出故幛 告
. 式中,Ⅵ Ⅱ是充电泵输 出电压 ;VDD是 电源
警信号。FLAG脚 输 出电压控制外 部电路 ,同
时也可通过 EN脚 关断稳压器。
∷
5.9限 流方法
:
振荡器i限 制充电泵输出电压∫该电压 比 VDD高
t6V∷ ∶
充电泵振荡器的工作频率为 “0kHz⒍ ∷
超低压差线性稳压器具有恒定电流限制。
・
:
电压。
∷∷
Vt・ |箝 位 电路通过 适时接通或关 断充电泵
误差放大器给充 电泵电路提供 1mA电 流
并利用充电泵输 出电压来驱动:MOsFET。 误差
为 F限 制输 出电流 ,取 样 电阻 Rs必 须接在
V1】 )脚 和 D(漏 极 )脚 之间的功率通路 中。
∶ 取样电阻两
端 的压降达到 ss血 V时 ,电 流
-17-
超低 压差 线性 稳压控 制 器 MIC51“ /5157/51ss
5.0V脚 都 不 接 S脚 时 ,稳 压 器 输 出 电 压 为
限制比较器使误差放大器的输出电压 降低 ,从
而避免取样电阻两端 电压超过 3smV。
6.应 用 电路
MIC51sB的 5V FB脚 接 EA脚 时,稳 压 器
输 出电压是 5V(不 需 外接分 压 电阻 )。
6,1MOSFET选 择
6.4.2可 调 输 出电压
准 N沟 道增强型 MOsFET,当 外部栅极驱动
电压 过 低时 ,可 选用逻辑 电平 N沟 道增强型
整 。为 了达到理 想效 果 ,R2可 选 10kΩ 电阻 ,如
图 4所 示 ,R1的 阻值 由下式计 算
MOSFET(MIC51“ ),当 输入 电源 电压过低
时,MIC51夕 /5158内 部的充 电泵可为标准型
MOsFET提 供所需的驱动电压。
.
MIC51“ (可 调型 )和 MIC51ss外 接分压
电阻后 ,输 出 电压 可 在 1.z35V~“ V之 间调
在大部分超低压差线性稳压器中都选择标
'
∷
12V。
:
R∴
^
6.2电 路布局
贯-1)
=1× 104frl夕
f二
6.5输 入滤波电容器
∷ .
为了适应负载电流在很宽的范围内变 化
并且消除误差放大器与充电泵之间的耦合 ,超
低压差线性稳压器输人端应 接人 只低 EsR
一
∵
的旁路电容。
∵
为 了获得最佳稳压效果 ,源 极 、
接地点和误
,
差放大器接点应当尽可能靠近负载 ,如 图 3所
示。
6.3MOsFET栅极 -源 极保护电路
除输 出电压可调 的规格外 ,MIC51“ 内部
都有栅极 -源 极箝位保护电路。采用输出电压
可调的器件时,为 了保护 MOSFET,栅 极和源
极间应接 △只 :“ V∷ 稳压管 ,如 图 3(c)所 示。
6.6输 出滤波电容 ∴
6.4输 出电压
6.4,1恒 定输 出电压
i
MIC515⒍ ∴
的 输 出 电 压 为 3.3V;
'3.⒊
MIC5156△ 5,0的 输 出电压为 5.0V。
MIC5157的 3.3V脚 接 S脚 时,稳 压器输
出电压为 3.3V。 MIC51s,的 5.0V脚 接 S脚
电容一般应选用容量较大的铝电解 电容 ,而 不
选 ESR较 小的电容器。因为输 出滤波电容的主
要作用不是 降低 ESR。 该电容的容量应当足够
输 出滤波电容可减少纹波 ,提 高负载调整
率。若 工作电压稳定 ,通 常不需接较大容量的
电容器。但是 ,为 了提高瞬变负载调整率 ,输 出∷
大 ,以 便提供与瞬变负载调整率∵致的大电流
I=C× dV/dJ。 当负载电流突增时:输 出电压
将降低。上式中,I代 表在时间 t内 负载电流的
增 量 。 该 式 表 明 .,在 负 载 两 端 并 联 一 只
0・ 0蜘F、 10uF的 薄膜 电
时 ,稳 压器 输 出电压为 5.OV。 当 3.3V脚 和
G
容器 ,可 大大提高瞬变 负
载响应能力。
C5iso
"∶
GND
(a)MI“ 15X‘ 恒爿
宦
输出电压电路
EA
i
(b)MIC515X可 调
(c)MIC51“ 可调
输 出电压 电路
输出电压电路
图 3 MIC515× 输 出电压 电路 图
图 4 电阻分压器连接电路图
-18-
《国外电子元器件》1998年 第9期 1998年 9月
⒍7电 流限制
为了取样输 出电流 ,应 在 VDr,脚 和 D脚 之
间接人阻值很小的电阻 Rs。 器件内部的限流 电
路限定取样电阻两端的电压 为 35mV。 取样电
阻 氐 的阻值可 由下式计算
屯源专辑
稳压器在电池达 到充 足电状态之|前 J可 提供
3smV/Rl的 恒定电流。
VFI'=1.235(1+R1/Rz)
‘
式中,VFL是 电池充足电电压。
(下 轳
-
:
Rs= 35mV
ILrM
闸极 电源
・ 式中,Rs为 取样电阻的阻值
∶
输 出电流。
6.8非 限流应用
,∶
LM为 最大
%
臼N
。
D
戈x
G
s
"Cs1∞
-0N0
若不需要限流 ,VDD脚 和 D脚 之间不需接
∷
取样电阻,如 图 5所 示。
,∷
6.93.3V微 处理器应用∵ °
-5V逻 辑来设 计 3.3V微 处理器时
FLAG输 出电压可对 5V电 源电压降额。可参
考 MIC51“ 方框 图外接元件。
6,10开 关电源 (sMPs)后 置稳压器 1 ∵ - ∷
MIcsl“ /515T/51ss系 列稳压器可作为
采用
v。
,
(a)大 电流 开关 电路
VD。
EN
开关电源的后置稳压器。加人超低压差线性稳
压器,可 大大降低峰 工峰值纹波电压。
∷∵
⒍ 11大 电流开关
:
Ⅲ Cs1sO
间内关断时,充 电泵电容器将会放完电。若给
充电泵电容充电使负载在达到工作电压之前产
生迟滞 :就 不能通过 EN脚 导通
断稳压器。
'关 使充电泵连
MIC51ss的 EN脚 保持高电平 ,可
v"
续工作。通过补偿误
差放大器输人可控制
’
MOsFET,
高端开关 ∷
如图 “b)所 示。
6.1z电 池充电器应用
MIC51ss在 电池
充电器 中可提供恒定
图 5不 限流时的连接电路图 电流,如 图 7所 示。该
s
EA
MIC51冗 /51夕/51sS系 列用于大电流开
关时,s脚 应悬空 ,如 图 “a)所 示。当器件发生
故 障时 ,接 在 MOsFET栅 极 和源极 之 间 的
16V稳 压管可保护 MOsFET。
如果 MIC51夕 或 M℃ 51ss用 于在给定时
G
GND
卫
嚣毖
夺
(b)快 速高端 开关 电路
图 6MIC51“ /T/g系 列应用开关 电路
Vw
EN
G
mIc5158 s
图 7 电池充电器 电路
.psO)
《国外电子元器件》1∞ 8年 第 9期
∶
tHM
冖
刀
”丿
8年 9月
电源专辑
x,冖
arnx`ε 饣
'
Bs.⒁
α
oρ
D・
GNocs
scι
⑾ 泌〓
Ι
Nˉ
图3
MAX1“ 7典 型应用电路
“
”
●设 定 充 电模 式 。
●通 过
●输人
MAX1647测 出充 电 电流 、充 电 电
⑾
sMBus地 址
0×
1T,ˉ
向
CMD7~
D0输 人 0× 14,此 后 D15~D0・ 就是充 电 电
流值 。记下该 二 进 制码 。
压。
●输人
sMBⅡ
地 址 0×
17,向
CMD7~
CMDO输 入 0× 5,此 后 D15~D0就 是 充 电电
由上 面所 得设 定 充 电电压 ,充 电电流 。
咨洵 编 号 四gOgO7
压 值 。记 下该 二 进 制码 。
雾 棼 赛 冢 癸 搴 棼 莽 雾 癸 界 抖 科 黏 黏 肀 莽 犭”
P1s) 当电池达到该电压时,MOSFET
关断。输 人 电源通过 R4对 电池涓流充电。
界 奉 莽 癸 瘀 棼 搴 棼 参 棼 癸 癸 棼 棼 棼 搴 棼 棼 漭 蔡 莽 棼
(上 接
⒗。
13不 间断电源
EN
V。 。
D
G
如 图 8所 示 ,MIC51夕 和 二 个 N沟 道
MOSFET在 不 间断电源中,可 起到电池转换的
作用。关断后 ,两 只ktDSFET的 源极与源极相
接 ,以 防止电流流过各 自的源极 -漏 极间的二
田
"IC5“
GND
s
EA
极管。同时,稳 压器应确保快速接通电池电路。
电池接通后 ,应 对交流电路进行监测以防止输
出电压 降至设计标准极限之下 。
咨询编号 :9BOgO4
图8
UPS电 源电路
MIC5156/5157/5158
Micrel
MIC5156/5157/5158
Super LDO™ Regulator Controller
Final Information
either 3.3V, 5.0V, or 12V. The MIC5158 can be configured as
a fixed 5V controller or programmed to any voltage from 1.3V
to 36V using two external resistors.
The MIC5156 is available in an 8-pin DIP or SOP. The
MIC5157 and MIC5158 are available in a 14-pin DIP or SOP
which operate from –40°C to +85°C.
General Description
The MIC5156, MIC5157, and MIC5158 Super Low-Dropout
(LDO) Regulator Controllers are single IC solutions for highcurrent low-dropout linear voltage regulation. Super LDO™
Regulators have the advantages of an external N-channel
power MOSFET as the linear pass element.
The MIC5156/7/8 family features a dropout voltage as low as
the RDS(ON) of the external power MOSFET multiplied by the
output current. The output current can be as high as the
largest MOSFETs can provide.
The MIC5156/7/8 family operates from 3V to 36V. The
MIC5156 requires an external gate drive supply to provide the
higher voltage needed to drive the gate of the external
MOSFET. The MIC5157 and MIC5158 each have an internal
charge pump tripler to produce the gate drive voltage. The
tripler is capable of providing enough voltage to drive a logiclevel MOSFET to 3.3V output from a 3.5V supply and is
clamped to 17.5V above the supply voltage. The tripler
requires three external capacitors.
The regulator output is constant-current limited when the
controller detects 35mV across an optional external sense
resistor. An active-low open-collector flag indicates a low
voltage of 8% or more below nominal output. A shutdown
(low) signal to the TTL-compatible enable control reduces
controller supply current to less than 1µA while forcing the
output voltage to ground.
The MIC5156-3.3 and MIC5156-5.0 controllers have internally fixed output voltages. The MIC5156 [adjustable] output
is configured using two external resistors. The MIC5157 is a
fixed output controller which is externally configured to select
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
4.5mA typical operating current
<1µA typical standby current
Low external parts count
Optional current limit (35mV typical threshold)
1% initial output voltage tolerance in most configurations
2% output voltage tolerance over temperature
Fixed output voltages of 3.3V, 5.0V (MIC5156)
Fixed output voltages of 3.3V, 5.0V, 12V (MIC5157)
Programmable (1.3 to 36V) with 2 resistors (MIC5156/8)
Internal charge pump voltage tripler (MIC5157/8)
Enable pin to activate or shutdown the regulator
Internal gate-to-source protective clamp
All versions available in DIP and SOP
Applications
•
•
•
•
•
Ultrahigh current ultralow dropout voltage regulator
Constant high-current source
Low parts count 5.0V to 3.3V computer supply
Low noise/low-dropout SMPS post regulator
High-current, current-limited switch
Typical Applications
+12V
1.0µF
5V
VDD
C1–
C1+
8
8
9
10
11
12 13
0.1µF
3mΩ
VIN
5V
47µF
RS
RS = 0.035V / ILIMIT
SMP60N03-10L
1
EN
2
3.3V
3
S
EN
7
S
G
D
VDD
6
4
MIC5157
MIC5156-3.3
5
5
FLAG
FLAG
6
D
GND
7
GND
1
G
2
C2–
3
C2+
4
VCP
0.1µF
Enable
Shutdown
VP
0.1µF
CL*
47µF
VOUT
3.3V, 10A
VIN
(3.61V min.)
3mΩ
47µF
RS
RS = 0.035V / ILIMIT
* Improves transient
response to load changes
IRLZ44 (Logic Level MOSFET)
10A 5V to 3.3V Desktop Computer Regulator
14
Enable
Shutdown
CL*
47µF
VOUT
3.3V, 10A
* Improves transient
response to load changes
10A Low-Dropout Voltage Regulator
Super LDO is a trademark of Micrel, Inc.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
March 1999
1
MIC5156/5157/5158
MIC5156/5157/5158
Micrel
Ordering Information MIC5156
Part Number
Temperature Range
Voltage
Package
MIC5156-3.3BN
–40°C to +85°C
3.3V
8-pin DIP
MIC5156-5.0BN
–40°C to +85°C
5.0V
8-pin DIP
MIC5156BN
–40°C to +85°C
Adjustable
8-pin DIP
MIC5156-3.3BM
–40°C to +85°C
3.3V
8-pin SOP
MIC5156-5.0BM
–40°C to +85°C
5.0V
8-pin SOP
MIC5156BM
–40°C to +85°C
Adjustable
8-pin SOP
Ordering Information MIC5157
Part Number
Temperature Range
Voltage
Package
MIC5157BN
–40°C to +85°C
Selectable
14-pin DIP
MIC5157BM
–40°C to +85°C
Selectable
14-pin SOP
Ordering Information MIC5158
Part Number
Temperature Range
Voltage
Package
MIC5158BN
–40°C to +85°C
5.0V/Adj.
14-pin DIP
MIC5158BM
–40°C to +85°C
5.0V/Adj.
14-pin SOP
Pin Configuration
MIC5156-x.x
EN 1
MIC5156
EN 1
8 S (Source)
8 EA
FLAG 2
7 D (Drain)
FLAG 2
7 D (Drain)
GND 3
6 G (Gate)
GND 3
6 G (Gate)
MIC5157
5V 1
3.3V 2
5 VD D
VP 4
5 VD D
VP 4
MIC5158
EA 1
14 EN
14 EN
13 S (Source)
5V FB 2
13 S (Source)
FLAG 3
12 D (Drain)
FLAG 3
12 D (Drain)
GND 4
11 G (Gate)
GND 4
11 G (Gate)
MIC5156/5157/5158
VCP 5
10 VD D
VCP 5
10 VD D
C2– 6
9 C1–
C2– 6
9 C1–
C2+ 7
8 C1+
C2+ 7
8 C1+
2
March 1999
MIC5156/5157/5158
Micrel
Pin Description MIC5156
Pin Number
Pin Name
Pin Function
1
EN
2
FLAG
Output Flag (Output): Open collector output is active (low) when VOUT is more
than 8% below nominal output. Circuit has 3% hysteresis.
3
GND
Circuit ground.
4
VP
N-channel Gate Drive Supply Voltage: User supplied voltage for driving the
gate of the external MOSFET.
5
VDD
Supply Voltage (Input): Supply voltage connection. Connect sense resistor
(RS) to VDD if current limiting used. Connect supply bypass capacitor to
ground near device.
6
G
Gate (Output): Drives the gate of the external MOSFET.
7
D
Drain and Current Limit (Input): Connect to external MOSFET drain and
external sense resistor (current limit), or connect to VDD and external MOSFET
drain (no current limit).
8 (3.3V, 5V)
S
Source (Input): Top of internal resistive divider chain. Connect directly to the
load for best load regulation.
8 (adjustable)
EA
Enable (Input): TTL high enables regulator; TTL low shuts down regulator.
Error Amplifier (Input): Connect to external resistive divider.
Pin Description MIC5157, MIC5158
Pin Number
Pin Name
1 (MIC5157)
5V
5V Configuration (Input): Connect to S (source) pin for 5V output.
1 (MIC5158)
EA
Error Amplifier (Input): Connect to external resistive divider to obtain adjustable output.
2 (MIC5157)
3.3V
2 (MIC5158)
5V FB
5V Feedback (Input): Connect to EA for fixed 5V output.
3
FLAG
Output Voltage Flag (Output): Open collector is active (low) when VOUT is 8%
or more below its nominal value.
4
GND
Circuit ground.
5
VCP
Voltage Tripler Output [Filter Capacitor]. Connect a 1 to 10µF capacitor to ground.
6
C2–
Charge Pump Capacitor 2: Second stage of internal voltage tripler. Connect a
0.1µF capacitor from C2+ to C2–.
7
C2+
Charge Pump Capacitor 2: See C2– pin 6.
8
C1+
Charge Pump Capacitor 1: First stage of internal voltage tripler. Connect a
0.1µF capacitor from C1+ to C1–.
9
C1–
Charge Pump Capacitor 1: See C1+ pin 8.
10
VDD
Supply Voltage (Input): Supply voltage connection. Connect sense resistor
(RS) to VDD if current limiting used. Connect supply bypass capacitor to
ground near device.
11
G
Gate (Output): Connect to External MOSFET gate.
12
D
Drain and Current Limit (Input): Connect to external MOSFET drain and
external sense resistor (current limit), or connect to VDD and external MOSFET
drain (no current limit).
13 (MIC5157)
S
Source and 3.3V/5V Configuration: Top of internal resistor chain. Connect to
source of external MOSFET for 3.3V, 5V, and 12V operation. Also see 3.3V
and 5V pin descriptions.
13 (MIC5158)
S
Source (Input): Top of internal resistor chain. Connect to top of external
resistive divider and source of external MOSFET.
14
EN
March 1999
Pin Function
3.3V Configuration (Input): Connect to S (source) pin for 3.3V output.
Enable (Input): TTL high enables regulator; TTL low shuts down regulator.
3
MIC5156/5157/5158
MIC5156/5157/5158
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Input (VDD) ...................................................... +38V
Enable Input (VEN) ......................................... –0.3V to 36V
Gate Output (VG) MIC5156 ......................................... +55V
Charge Pump Node (VCP) MIC5157/8 ........................ +55V
Source Connection (VS) .................................... 1.3 to +36V
Flag (VFLAG) .................................................... –0.3 to +40V
Storage Temperature (TS) ....................... –65°C to +150°C
Lead Temperature (soldering 10 sec.) ...................... 300°C
Ambient Temperature Range (TA)
MIC515xBM/BN ..................................... –40°C to +85°C
Junction Temperature (TJ) ...................................... +150°C
Thermal Resistance (θJA)
Package
MIC5156
MIC5157/8
DIP ............................... 100°C/W ..................... 90°C/W
SOP .............................. 160°C/W ................... 120°C/W
Electrical Characteristics(Note 5)
VDD = 5V, VEN = 5V; TA = 25°C; unless noted.
Symbol
Parameter
Condition
Min
VDD
Supply Voltage
IDD(ON)
IDD(OFF)
Supply Current MIC5156
Operating, VEN = 5V
Shutdown, VEN = 0V
IDD(ON)
IDD(OFF)
Supply Current MIC5157/8
Operating, VEN = 5V
Shutdown, VEN = 0V
VIH
VIL
Enable Input Threshold
High
Low
EN IB
Enable Input Bias Current
VEN = 2.4V
VCP
Max. Charge Pump Voltage
VCP – VDD, VDD > 10V
fCP
Charge Pump Frequency
VOUT MAX
Maximum Gate Drive Voltage
(MIC5157/8)
VSOURCE = 0V
VDD = 3.5V
VDD = 5V
VDD = 12V
VOUT MIN
Minimum Gate Drive Voltage
VSOURCE > VOUT(NOM)
VLIM
Current Limit Threshold
VDD – VD @ ILIM
VS
Source Voltage
Typ
Max
Units
36
V
2.7
0.1
10
5
mA
µA
4.5
0.1
10
5
mA
µA
1.3
1.3
0.8
V
V
20
25
µA
17.5
18.5
V
3
2.4
160
5
9
24
7.0
11.3
28
kHz
9
15
30
1.0
V
V
V
V
28
35
42
mV
Short G (gate) to (S) source, Note 4
MIC5156-3.3
MIC5156-5.0
MIC5157, 3.3V pin to S pin (3.3V config.)
MIC5157, 5V pin to S pin (5V config.)
MIC5157, VDD = 7V, (12V config.)
MIC5158, 5V FB pin to EA pin (5V config.)
3.267
4.950
3.250
4.950
11.70
4.925
3.3
5.0
3.3
5.0
12
5.0
3.333
5.050
3.350
5.050
12.30
5.075
V
V
V
V
V
V
1.222
1.235
1.248
V
2
7
mV
16.6
20
V
VBG
Bandgap Reference Voltage
MIC5156 [adjustable] and MIC5158
VLR
Output Voltage Line Regulation
5V < VDD < 15V, VOUT = 3.3V
VGS MAX
Gate to Source Clamp
VFT
Flag Comparator Threshold
% of nominal VSOURCE
92
%
VFH
Flag Comparator Hysteresis
% of nominal VSOURCE
3
%
VSAT
Flag Comparator Sat. Voltage
IFLAG = 1mA
14
0.09
Note 1.
Exceeding the absolute maximum rating may damage the device.
Note 2.
The device is not guaranteed to function outside its operating rating.
Note 3.
Devices are ESD sensitive. Handling precautions recommended.
Note 4.
Test configuration. External MOSFET not used.
Note 5.
Specification for packaged product only.
MIC5156/5157/5158
4
0.2
V
March 1999
MIC5156/5157/5158
Micrel
Typical Characteristics
5.0V Regulator Output
Voltage vs. Temperature
3.33
5.03
10
3.31
3.30
3.29
3.28
3.27
MIC5157/8 On-State Supply
Current vs. Supply Voltage
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
0
5
10 15 20 25
SUPPLY VOLTAGE (V)
30
5.01
5.00
4.99
4.98
4.96
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
MIC5157/8 On-State Supply
Current vs. Temperature
5.0
4.5
4.0
3.5
3.0
2.5
VDD = 5V
2.0
1.5
1.0
0.5
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
10
150
125
100
75
50
25
0
5
10 15 20 25
SUPPLY VOLTAGE (V)
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
30
Enable Threshold Voltage
vs. Temperature
Enable Input Bias Current
vs. Enable Voltage
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
March 1999
120
ENABLE BIAS CURRENT (µA)
ENABLE THRESHOLD VOLTAGE (V)
0
VDD = 5V
IFLAG = 1mA
175
20
4
LOGIC
INPUT
2
3.3V
OUTPUT
100
80
60
40
20
0
0
2
4 6 8 10 12 14 16
ENABLE VOLTAGE (V)
5
0.0
0.2
0.4
TIME (ms)
0.6
Off-State Supply Current
vs. Temperature
5.0
4.5
VDD = 5V
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Flag Output Voltage
vs. Flag Current
200
30
CCP = 1µF
CL = 50µF
6
-2
-0.2
1.0
0.9
FLAG VOLTAGE (V)
60
40
8
Flag Output Voltage
vs. Temperature
FLAG VOLTAGE (mV)
CHARGE PUMP VOLTAGE (V)
Charge-Pump Output Voltage
vs. Supply Voltage
50
MOSFET = IRF540
VIN = 5V, IL = 0.5A
CC1 = CC2 = 0.1µF
0
4.97
VDD = 5V
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
CURRENT LIMIT THRESHOLD (mV)
2.0
5.02
OFF-STATE SUPPLY CURRENT (µA)
3.32
VOLTAGE (V)
OUTPUT VOLTAGE (V)
12
3.26
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
ON-STATE SUPPLY CURRENT (mA)
MIC5157/8 Turn-On
Response Time for 3.3V
5.04
ON-STATE SUPPLY CURRENT (mA)
OUTPUT VOLTAGE (V)
3.3V Regulator Output
Voltage vs. Temperature
3.34
0
2
4
6
8
10
FLAG SINK CURRENT (mA)
Current Limit Threshold
vs. Temperature
70
60
50
40
30
20
10
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
MIC5156/5157/5158
MIC5156/5157/5158
Micrel
Block Diagram MIC5156
+12V Input
+5V Input
0.1µF
VP
VDD
Internal
Bias
EN
RS
3mΩ
Enable
Shutdown
12k
to all
internal blocks
ILIMIT
Comparator
D (Drain)
[ILIMIT]
35mV
1.235V
Bandgap
Reference
+5V Input
Q2
FLAG
G (Gate)
Error
Amp
16.6V
Q1
SMP60N03-10L
S* (Source)
Regulated
+3.3V Output
75mV
* fixed version only
† 3.3V = 17k, 5V = 32k
‡
17k†
10k
GND
CL
Load 1
Load 2
Switched
5V Load
VOUT
Comparator
EA‡
adjustable version only
Block Diagram with External Components
Fixed 3.3V Power Supply with 5.0V Load Switch
Block Diagram MIC5157
+5V Input
0.1µF
C1+
Oscillator
C1 0.1µF
C1–
C2+
C3
1µF
C2
C2–
VCP
VDD
VCP
Clamp
Charge Pump
Tripler
Internal
Bias
ILIMIT
Comparator
35mV
FLAG
RS
3mΩ
Enable
Shutdown
to all
internal blocks
1.235V
Bandgap
Reference
VOUT
Comparator
EN
D (Drain)
[ILIMIT]
G (Gate)
Error
Amp
16.6V
Q1
IRFZ44
S (Source)*
Regulated
+3.3V Output
75mV
58k
15k
5V
CL
3.3V
10k
Load
17k
GND
Block Diagram with External Components
Fixed 3.3V 10A Power Supply
MIC5156/5157/5158
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March 1999
MIC5156/5157/5158
Micrel
Block Diagram MIC5158
+5V Input
0.1µF
C1+
Oscillator
C1 0.1µF
C1–
C2+
C3
1µF
C2
C2–
VCP
VDD
VCP
Clamp
Charge Pump
Tripler
Internal
Bias
ILIMIT
Comparator
35mV
FLAG
RS
3mΩ
Enable
Shutdown
to all
internal blocks
1.235V
Bandgap
Reference
VOUT
Comparator
EN
D (Drain)
[ILIMIT]
G (Gate)
Error
Amp
16.6V
Q1
IRFZ44
S (Source)
Regulated
+3.6V Output
32k
10k
5V
FB
CL
Load
75mV
GND
EA
19.1k
10.0k
Block Diagram with External Components
Adjustable Power Supply, 3.6V Configuration
MOSFET (regulator pass element) placed between the supply and the load. The gate-to-source voltage may vary from
1V to 16V depending upon the supply and load conditions.
Because the source voltage (output) approaches the drain
voltage (input) when the regulator is in dropout and the
MOSFET is fully enhanced, an additional higher supply
voltage is required to produce the necessary gate-to-source
enhancement. This higher gate drive voltage is provided by
an external gate drive supply (MIC5156) or by an internal
charge pump (MIC5157 and MIC5158).
Gate Drive Supply Voltage (MIC5156 only)
The gate drive supply voltage must not be more than 14V
above the supply voltage (VP – VDD < 14V). The minimum
necessary gate drive supply voltage is:
VP = VOUT + VGS + 1
where:
Functional Description
A Super LDO Regulator is a complete regulator built around
Micrel’s Super LDO Regulator Controller.
Refer to Block Diagrams MIC5156, MIC5157, and MIC5158.
Version Differences
The MIC5156 requires an external voltage for MOSFET gate
drive and is available in 3.3V fixed output, 5V fixed output, or
adjustable output versions. With 8-pins, the MIC5156 is the
smallest of the Super LDO Regulator Controllers.
The MIC5157 and MIC5158 each have an internal charge
pump which provides MOSFET gate drive voltage. The
MIC5157 has a selectable fixed output of 3.3V, 5V, or 12V.
The MIC5158 may be configured for a fixed 5V or adjustable
output.
Enable (EN)
With at least 3.0V on VDD, applying a TTL low to EN places
the controller in shutdown mode. A TTL high on EN enables
the internal bias circuit which powers all internal circuitry. EN
must be pulled high if unused. The voltage applied to EN may
be as high as 36V.
The controller draws less than 1µA in shutdown mode.
Gate Enhancement
The Super LDO Regulator Controller manages the gate-tosource enhancement voltage for an external N-channel
March 1999
VP = gate drive supply voltage
VOUT = regulator output voltage
VGS = gate-to-source voltage for full
MOSFET gate enhancement
The error amplifier uses the gate drive supply voltage to drive
the gate of the external MOSFET. The error amplifier output
can swing to within 1V of VP.
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MIC5156/5157/5158
MIC5156/5157/5158
Micrel
Charge Pump (MIC5157/5158 only)
The charge pump tripler creates a dc voltage across reservoir
capacitor C3. External capacitors C1 and C2 provide the
necessary storage for the stages of the charge pump tripler.
The tripler’s approximate dc output voltage is:
VCP ≈ 3 (VDD – 1)
where:
VCP = charge pump output voltage
VDD = supply voltage
The VCP clamp circuit limits the charge pump voltage to 16V
above VDD by gating the charge pump oscillator ON or OFF
as required. The charge pump oscillator operates at 160kHz.
The error amplifier uses the charge pump voltage to drive the
gate of the external MOSFET. It provides a constant load of
about 1mA to the charge pump. The error amplifier output can
swing to within 1V of VCP.
Although the MIC5157/8 is designed to provide gate drive
using its internal charge pump, an external gate drive supply
voltage can be applied to VCP . When using an external gate
drive supply, VCP must not be forced more than 14V higher
than VDD.
When constant loads are driven, the ON/OFF switching of the
charge pump may be evident on the output waveform. This is
caused by the charge pump switching ON and rapidly increasing the supply voltage to the error amplifier. The period
of this small charge pump excitation is determined by a
number of factors: the input voltage, the 1mA op-amp load,
any dc leakage associated with the MOSFET gate circuit, the
size of the charge pump capacitors, the size of the charge
pump reservoir capacitor, and the characteristics of the input
voltage and load. The period is lengthened by increasing the
charge pump reservoir capacitor (C3). The amplitude is
reduced by weakening the charge pump—this is accomplished by reducing the size of the pump capacitors (C1 and
C2). If this small burst is a problem in the application, use a
10µF reservoir capacitor at C3 and 0.01µF pump capacitors
at C1 and C2. Note that the recovery time to repetitive load
transients may be affected with small pump capacitors.
Gate-to-Source Clamp
A gate-to-source protective voltage clamp of 16.6V protects
the MOSFET in the event that the output voltage is suddenly
forced to zero volts. This prevents damage to the external
MOSFET during shorted load conditions. Refer to “Charge
Pump” for normal clamp circuit operation.
The source connection required by the gate-to-source clamp
is not available on the adjustable version of the MIC5156.
Output Regulation
At start-up, the error amplifier feedback voltage (EA), or
internal feedback on fixed versions, is below nominal when
compared to the internal 1.235V bandgap reference. This
forces the error amplifier output high which turns on external
MOSFET Q1. Once the output reaches regulation, the controller maintains constant output voltage under changing
input and load conditions by adjusting the error amplifier
output voltage (gate enhancement voltage) according to the
feedback voltage.
Out-of-Regulation Detection
When the output voltage is 8% or more below nominal, the
open-collector FLAG output (normally high) is forced low to
signal a fault condition. The FLAG output can be used to
signal or control external circuitry. The FLAG output can also
be used to shut down the regulator using the EN control.
Current Limiting
Super LDO Regulators perform constant-current limiting (not
foldback). To implement current limiting, a sense resistor
(RS) must be placed in the “power” path between VDD and D
(drain).
If the voltage drop across the sense resistor reaches 35mV,
the current limit comparator reduces the error amplifier output. The error amplifier output is decreased only enough to
reduce the output current, keeping the voltage across the
sense resistor from exceeding 35mV.
Application Information
MOSFET Selection
Standard N-channel enhancement-mode MOSFETs are acceptable for most Super LDO regulator applications.
Logic-level N-channel enhancement-mode MOSFETs may
be necessary if the external gate drive voltage is too low
(MIC5156), or the input voltage is too low, to provide adequate charge pump voltage (MIC5157/8) to enhance a
standard MOSFET.
Circuit Layout
For the best voltage regulation, place the source, ground, and
error amplifier connections as close as possible to the load.
See figures (1a) and (1b).
MIC5156/5157/5158
VIN
G
GND
S
Load
MIC515x
Figure 1a. Connections for Fixed Output
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March 1999
MIC5156/5157/5158
Micrel
Adjustable Configurations
Micrel’s MIC5156 [adjustable] and MIC5158 require an external resistive divider to set the output voltage from 1.235V to
36V. For best results, use a 10kΩ resistor for R2. See
equation (1) and figure (2).
VIN
G
S
Load
MIC5157
or
MIC5158
EA
GND
1)
V
R1 = 1× 104 OUT − 1
1.235
G
VOUT
S
Figure 1b. Connections for Adjustable Output
MIC5157/8
GND
VIN
R1
EA*
R2
10k
G
*
MIC5156
EA
GND
Load
Figure 2. Typical Resistive Divider
Input Filter Capacitor
The Super LDO requires an input bypass capacitor for
accommodating wide changes in load current and for decoupling the error amplifier and charge pump. A medium to large
value low-ESR (equivalent series resistance) capacitor is
best, mounted close to the device.
* Optional 16V zener diode
recommended in applications
where VG is greater than 18V
Figure 1c. MIC5156 Connections for
Adjustable Output
Output Filter Capacitor
An output filter capacitor may be used to reduce ripple and
improve load regulation. Stable operation does not require a
large capacitor, but for transient load regulation the size of the
output capacitor may become a consideration. Common
aluminum electrolytic capacitors perform nicely; very lowESR capacitors are not necessary. Increased capacitance
(rather than reduced ESR) is preferred. The capacitor value
should be large enough to provide sufficient I = C × dV/dt
current consistent with the required transient load regulation
quality. For a given step increase in load current, the output
voltage will drop by about dV = I × dt/C, where I represents the
increase in load current over time t. This relationship assumes that all output current was being supplied via the
MOSFET pass device prior to the load increase. Small
(0.01µF to 10µF) film capacitors parallel to the load will further
improve response to transient loads.
Some linear regulators specify a minimum required output
filter capacitance because the capacitor determines the
dominant pole of the system, and thereby stabilizes the
system. This is not the situation for the MIC5156/7/8; its
dominant pole is determined within its error amplifier.
MOSFET Gate-to-Source Protection
When using the adjustable version of the MIC5156, an
external 16V zener diode placed from gate-to-source is
recommended for MOSFET protection. All other versions of
the Super LDO regulator controller use the internal gate-tosource clamp.
Output Voltage Configuration
Fixed Configurations
The MIC5156-3.3 and MIC5156-5.0 are preset for 3.3V and
5.0V respectively.
The MIC5157 operates at 3.3V when the 3.3V pin is connected to the S (source) pin; 5.0V when the 5.0V pin is
connected to the S pin; or 12V if the 3.3V and 5.0V pins are
open.
The MIC5158 operates at a fixed 5V (without an external
resistive divider) if the 5V FB pin is connected to EA.
March 1999
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MIC5156/5157/5158
MIC5156/5157/5158
Micrel
Current Limiting
Current sensing requires a low-value series resistance (Rs)
between VDD and D (drain). Refer to the typical applications.
The internal current-limiting circuit limits the voltage drop
across the sense resistor to 35mV. Equation (2) provides the
sense resistor value required for a given maximum current.
Gate Supply
Enable
Shutdown
VG
EN
VIN
RS
VDD
D
MIC5156-x.x G
RS =
35mV
ILIM
S
GND
Load
2)
where:
RS = sense resistor value
ILIM = maximum output current
Most current-limited applications require low-value resistors.
See Application Hints 21 and 25 for construction hints.
Non-Current-Limited Applications
For circuits not requiring current limiting, do not use a sense
resistor between VDD and D (drain). See figure (3). The
controller will not limit current when it does not detect a 35mV
drop from VDD to D.
Figure 4a. High-Side Switch
If a MIC5157 or MIC5158 is used and is shutdown for a given
time, the charge pump reservoir VCP will bleed off. If recharging the reservoir causes an unacceptable delay in the load
reaching its operating voltage, do not use the EN pin for on/
off control. Instead, use the MIC5158, hold EN high to keep
the charge pump in continuous operation, and switch the
MOSFET on or off by overriding the error amplifier input as
shown in figure (4b).
VIN
VIN
VDD
D
G
VDD
S
EN
G
S
MIC5158
Figure 3. No Current Limit
3.3V Microprocessor Applications
For computer designs that use 3.3V microprocessors with 5V
logic, the FLAG output can be used to suppress the 5V supply
until the 3.3V output is in regulation. Refer to the external
components shown with the MIC5156 Block Diagram.
SMPS Post Regulator Application
A Super LDO regulator can be used as a post regulator for a
switch-mode power supply. The Super LDO regulator can
provide a significant reduction in peak-to-peak ripple voltage.
High-Current Switch Application
All versions of the MIC5156/7/8 may be used for currentlimited, high-current, high-side switching with or without
voltage regulation. See figure (4a). Simply leave the “S”
terminal open. A 16V zener diode from the gate to the source
of the MOSFET protects the MOSFET from overdrive during
fault conditions.
EA
GND
Output Off
Output On
Load
MIC5156
1N4148
Figure 4b. Fast High-Side Switch
Battery Charger Application
The MIC5158 may be used in constant-current applications
such as battery chargers. See figure (5). The regulator
supplies a constant-current (35mV ÷ R3) until the battery
approaches the float voltage:
R1
VFL = 1. 235 1 +
R2
where:
VFL = float voltage
At float voltage, the MOSFET is shut off. A trickle charge is
supplied by R4.
MIC5156/5157/5158
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March 1999
MIC5156/5157/5158
Micrel
Uninterruptible Power Supply
The MIC5157 and two N-channel MOSFETs provide battery
switching for uninterruptible power as shown in figure (6).
Two MOSFETs are placed source-to-source to prevent current flow through their body diodes when switched off. The
Super LDO regulator is continuously enabled to achieve fast
battery switch-in. Careful attention must be paid to the ac-line
monitoring circuitry to ensure that the output voltage does not
fall below design limits while the battery is being switched in.
VIN
R3
VDD
R4
D
EN
G
MIC5158
S
R1
EA
GND
R2
VDD
EN
D
Q1
G
S
MIC5158
Figure 5. Battery Charger Concept
D
G
S
S
MOSFET body diodes
shown for clarity
G
GND
Line
Battery
AC
Line
EA
Q2
D
40V max.
1N4148
Off-line
Power Supply
Uninterruptable
DC
Figure 6. UPS Power Supply Concept
March 1999
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MIC5156/5157/5158
MIC5156/5157/5158
Micrel
Package Information
PIN 1
DIMENSIONS:
INCH (MM)
0.380 (9.65)
0.370 (9.40)
0.255 (6.48)
0.245 (6.22)
0.135 (3.43)
0.125 (3.18)
0.300 (7.62)
0.013 (0.330)
0.010 (0.254)
0.018 (0.57)
0.130 (3.30)
0.100 (2.54)
0.380 (9.65)
0.320 (8.13)
0.0375 (0.952)
8-Pin DIP (N)
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
TYP
0.064 (1.63)
0.045 (1.14)
0.197 (5.0)
0.189 (4.8)
0.020 (0.51)
0.013 (0.33)
0.0098 (0.249)
0.0040 (0.102)
0°–8°
SEATING
PLANE
45°
0.010 (0.25)
0.007 (0.18)
0.050 (1.27)
0.016 (0.40)
0.244 (6.20)
0.228 (5.79)
8-Pin SOP (M)
MIC5156/5157/5158
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March 1999
MIC5156/5157/5158
Micrel
.770 (19.558) MAX
PIN 1
.235 (5.969)
.215 (5.461)
.060 (1.524)
.045 (1.143)
.310 (7.874)
.280 (7.112)
.160 MAX
(4.064)
.080 (1.524)
.015 (0.381)
.015 (0.381)
.008 (0.2032)
.160 (4.064)
.100 (2.540)
.110 (2.794)
.090 (2.296)
.023 (.5842)
.015 (.3810)
.060 (1.524)
.045 (1.143)
.400 (10.180)
.330 (8.362)
14-Pin DIP (N)
PIN 1
DIMENSIONS:
INCHES (MM)
0.154 (3.90)
0.026 (0.65)
MAX)
0.193 (4.90)
0.050 (1.27) 0.016 (0.40)
TYP
TYP
45°
0.006 (0.15)
0.057 (1.45)
0.049 (1.25)
0.344 (8.75)
0.337 (8.55)
SEATING
PLANE
3°–6°
0.244 (6.20)
0.228 (5.80)
14-Pin SOP (M)
March 1999
13
MIC5156/5157/5158
MIC5156/5157/5158
MIC5156/5157/5158
Micrel
14
March 1999
MIC5156/5157/5158
March 1999
Micrel
15
MIC5156/5157/5158
MIC5156/5157/5158
Micrel
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
USA
http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
© 1999 Micrel Incorporated
MIC5156/5157/5158
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March 1999