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| 型号： | MAX669EUB+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 9/18页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR PWM HYBRID 10-UMAX |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式，混合 |
| 输出数： | 1 |
| 频率 - 最大： | 575kHz |
| 占空比： | 94% |
| 电源电压： | 1.8 V ~ 28 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
MAX668/MAX669
1.8V to 28V Input, PWM Step-Up
Controllers in μMAX
PWM Controller
The heart of the MAX668/MAX669 current-mode PWM
controller is a BiCMOS multi-input comparator that
simultaneously processes the output-error signal, the
current-sense signal, and a slope-compensation ramp
(Figure 1). The main PWM comparator is direct sum-
ming, lacking a traditional error amplifier and its associ-
ated phase shift. The direct summing configuration
approaches ideal cycle-by-cycle control over the out-
put voltage since there is no conventional error amp in
the feedback path.
In PWM mode, the controller uses fixed-frequency, cur-
rent-mode operation where the duty ratio is set by the
input/output voltage ratio (duty ratio = (V OUT - V IN ) / V IN
in the boost configuration). The current-mode feedback
loop regulates peak inductor current as a function of
the output error signal.
At light loads the controller enters Idle Mode. During
Idle Mode, switching pulses are provided only as need-
ed to service the load, and operating current is mini-
mized to provide best light-load efficiency. The
minimum-current comparator threshold is 15mV, or 15%
of the full-load value (I MAX ) of 100mV. When the con-
troller is synchronized to an external clock, Idle Mode
occurs only at very light loads.
Bootstrapped/Non-Bootstrapped Operation
Low-Dropout Regulator (LDO)
Several IC biasing options, including bootstrapped and
non-bootstrapped operation, are made possible by an
on-chip, low-dropout 5V regulator. The regulator input is
at V CC , while its output is at LDO. All MAX668/MAX669
functions, including EXT, are internally powered from
LDO. The V CC -to-LDO dropout voltage is typically
200mV (300mV max at 12mA), so that when V CC is less
than 5.2V, LDO is typically V CC - 200mV. When LDO is
in dropout, the MAX668/MAX669 still operate with V CC
as low as 3V (as long as LDO exceeds 2.7V), but with
reduced amplitude FET drive at EXT. The maximum
V CC input voltage is 28V.
LDO can supply up to 12mA to power the IC, supply
gate charge through EXT to the external FET, and sup-
ply small external loads. When driving particularly large
FETs at high switching rates, little or no LDO current
may be available for external loads. For example, when
switched at 500kHz, a large FET with 20nC gate charge
requires 20nC x 500kHz, or 10mA.
V CC and LDO allow a variety of biasing connections to
optimize efficiency, circuit quiescent current, and full-
load start-up behavior for different input and output
voltage ranges. Connections are shown in Figures 2, 3,
4, and 5. The characteristics of each are outlined in
Table 1.
V CC
1.25V
MAX669 ONLY
LDO
ANTISAT
LDO
R1
552k
EXT
PGND
MUX 0
1
LOW-VOLTAGE
START-UP
OSCILLATOR
(MAX669 ONLY)
UVLO
MAX668
R2
276k
R3
276k
MAIN PWM
1.25V
REF
MAX669
FB
CS+
100mV
CURRENT SENSE
SLOPE COMPENSATION
I MAX
+A
-A X6
+C
-C X1
+S X1
-S
COMPARATOR
SYNC/SHDN
FREQ
BIAS
OSC
OSC
S Q
15mV
I MIN
R
Figure 1. MAX668/MAX669 Functional Diagram
Maxim Integrated
9
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